ALBERT R. MANN LIBRARY AT CORNELL UNIVERSITY DATE DUE MAY 1 i im-s^. rtHl - — mnJ 1 ^\m isH^^ l^ I. ' A 4 n-j"- •'T'r|8 r ^ "^ ^ ™ i\^AY e ' '■^.^: 1 b n ? li CAYLORO PBINTCOINU.S.A Cornell University Library SB 608.I4P4 The diseases and pests of the rubber tre 3 1924 002 855 280 Cornell University Library The original of tiiis book is in tine Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924002855280 THE DISEASES AND PESTS OF THE RUBBER TREE MACMILLAN AND CO., Limited LONDON • BOMBAY • CALCUTTA • MADRAS MELBOURNE THE MACMILLAN COMPANY NEW YORK • BOSTON • CHICAGO DALLAS • SAN FRANCISCO THE MACMILLAN CO. OF CANADA, Ltd. TORONTO Plate I, FOMES LIONOSUS Upper surface Specimen half dry THE DISEASES AND PESTS OF THE- RUBBER TREE BY T. FETCH, B.A., B.Sc. BOTANIST AND MYCOLOGIST TO THE GOVERNMENT OF CEYLON MACMILLAN AND CO., LIMITED ST. MARTIN'S STREET, LONDON 1921 COPYRIGHT (^ l^y^y PEEFACE In 1911 the diseases wHcli were known to attack the rubber tree were described in The Physiology and Diseases of Hevea hrasilimsis. The number of recorded diseases was then comparatively small, and it was possible to include with them a general account of the structure and physiology of the tree, and a summary of those tapping experiments which promised to afford a foundation for a theory of rubber tapping. That book has now been out of priiit for some time, and several inquirers have suggested the issue of a second edition. But the number of known diseases of Hevea has, unfortunately, been considerably extended duriiig the last eight years, while the work of numerous investigators in this field has added largely to our knowledge of both old and new ones. Consequently, rubber diseases now demand a volume to themselves ; and it has therefore been decided to divide the subject-matter of the former book, and to publish a separate account, revised and brought up to date, of the diseases and pests only. It is hoped that it wiU be possible, at some future date, to deal similarly with the other half of the original volume. As the book is intended primarily for the rubber planter, technical botanical details have been avoided as much as possible. It is not practicable to exclude them altogether, nor, indeed, is that necessary, for rubber cultivation has made the planter familiar with technical botanical terms to a degree hitherto unknown in tropical agriculture. Micro- scopic details of the fungi have in general been omitted, the scientific descriptions of them, which are of value only to a vi THE RUBBER TREE mycologist, being included in a separate chapter for the convenience of those who may desire to refer to them. The illustrations have been chosen with the idea of enabling the planter to identify the different diseases. They ; represent typical stages of the various fungi or diseases,^ but, as fungi are usually highly variable, one cannot figure all stages without making the cost of the book prohibitive. ^ A brief summary of the diseases described, with references i to -the illustrations, has been added to each of the principal chapters. These, it is hoped, will prove of service in a rapid survey for purposes of identification. A chapter on the priacipal pests of Hevea has been in- cluded. Up to the present, insect pests of Hevea, with the exception of the notorious Termes gestroi, have proved of minor importance in comparison with fungus diseases. The aim of a book of this kind is not only to provide the planter with a means of identifying and dealing with known diseases, but also to enable him to decide whether any observed abnormal appearance or disease is unrecorded and consequently ought to be brought to the notice of a myco- logist. Rubber cultivation demands constant vigilance in this respect, since, because of the greater value of the in- dividual plant and the unique method of obtaining the crop, an outbreak of disease may have a more serious result than in the case of such products as tea, sugar, etc. That the future of plantation rubber is largely dependent. upon the elective combating of disease has been repeatedly emphasised; and it is the duty of rubber planters, and those responsible for the management of rubber estates, to resist any attempt to minimise the importance of that aspect of rubber cidtiva- tion and research. CONTENTS OHAPTEE I PAQE General Sanitation ...... 1 Jungle stumps. Thinning out. Intercrops, cover plants, etc. Pruning. The protection of wounds. Scraping.' Forking. Tree surgery. Oleaning-up forks. CHAPTEB II EooT Diseases . . . . . . .21 I^oot diseases in general. Fames lignosas. Brown Boot disease (Fames lamaaensis). Wet rot {Fames psevdo-ferreus). Red Root disease (Poria hypobrunnea). Ustulina zanata. Sphaerastilbe repens. Eoot disease of " Stumps " (Botryodiplodia Theobromae). Polyporus rvigulosus. Wounds on exposed lateral roots. • Summary. CHAPTEK III Leaf Diseases . . . . . ■ .77 South American leaf disease (Fusidadium macrasporwm). Bird's- eye spot (Helminthospariwm Heveae). Shot-hole leaf disease. Gata- cawna Hiiberi. Rim Blights. Ascochyta Rim Blight; Sphaeirella Rim Blight. Guignardia Rim Blight. Indeterminate leaf spots. Red Rust. Abnormal leaf-fall. Mildew. Sooty Moulds. Nodules on leaves. Summary. CHAPTEE IV Pbytopethora Diseases . . • • .100 Abnormal leaf-fall and pod disease. Die-back of shoots. Claret- coloured Canker, Purple Canker, or iPatch Canker. Black Thread disease. The fungi. Summary. PAGE 134 viii THE RUBBER TREE CHAPTEE V Stem Diseasbs ...-•■• Pink disease. Udulina zonata. Death of green twigs. Die- back. Fasidadium stem disease Monldv rot of the tapped snrface. Thread Blight. White Stem Blight Horse-hair Blight Top Canker. A stem disease of seedlings. Loranthus. Sununaiy. CHAPTEE VI NoN-PARAsmc Diseases, Abxorjiaijties, etc. . .169 Brown Bast Xodnles. Globular shoots. Fasciation. Twisted seedlings. Cork warts. Malformed stems. A twisted Hevea stem. Scorched trees. Black patches in Hecea wood. lightning injuries. Gradations of latex. Rubber pad& CHAPTER VII Prepared Robber ...... 208 Colonted spots. Rust Black scrap. Tacky mbber. Moulds on mbber. Effect of Bordeanx mixture on rubber. CHAPTER Vm Pests of Hevea . . . . . .223 l^fammals. White ants. Root and stem borer of Herea {Bato- eera ni6iu). Boring beetles in generaL Bark-eating caterpQlars. Mites. Locusts. Scale insects. Ants. Cockchafer grabs. Bark- I eating beetles. Rhinoceros beetles. Swarming cat«rpil]ai& Crickets. Slugs. CHAPTER IX Miscellanea ....... 249 The effect of preserratiTes on renewing bark. Lime-sulpfanr solution. Bordeaux: mixture. Wobum Bordeaux. CHAPTER X Fungi ox Hbyba ..... 261 BIBLIOGRAPHY . . . . 268 INDEX .... ... 275 ILLUSTRATIONS IN COLOUK PLATE FACING PAGE I. Fames lignosus . ... Frontispiece II. Root diseases of Hevea .... .48 Fig. 1, Fames lignosus, upper surface, x ^ ; Fig. 2, i'omes lignosus, lower surface, natural size ; Fig. 3, Fames lignosus, section, natural size ; Fig. 4, mycelium of Fames lignosus ; Fig. 5, Poria hypohrwnnea, fructification, fully developed, natural size ; Fig. 6, Poria hypo- brunnea, section, x 3 ; Fig. 7, Bevea root, attacked by Brown Root disease, showing brown lines ; Fig. 8, wood attacked by Brown Root disease, showing brown bands ; Fig. 9, Fames lamaoensis, section, natural size, pale specimen ; Fig. 10, Fames lamaoensis, upper sur- face, X ^. III. Leaf and stem diseases . . ... 80 Fig. 1, Die-back caused by Glaeosporium, x | ; Fig. 2, fructification of Horse-hair Blight, natural size ; Fig. 3, leaf attacked by Guig- nardia Seveae, natural size ; Fig. 4, leaf attacked by Helminthasporium Reveae, natural size ; Fig. 5, \ea.{ a,tta.ck.edhy Ascochyta Heveae, natural size ; Fig. 6, leaf attacked by Phyllosticta Heveae and Colletotrichum Heveae, natural size. IV. Claret-coloured Canker . . . .112 Patch exposed by shaving. V. Stem and root diseases ... . 176 Fig. 1, Pink disease, old stage ; Fig. 2, Pink disease, strands and pink cushions ; Fig. 3, Poria hypobrunnea, red lines in wood ; Fig. 4, Poria hypobrunnea, young mycelium on root ; Fig. 5, Brown Bast, section of cortex showing the brown line near the cambium and the normal red line found in renewing bark ; Fig. 6, Brown Bast, section of cortex, showing the forpiation of a scale ; Fig. 7, Brown Bast, dis- coloration exposed by shaving. All natural size. • VI. Pests of Hevea ..... . 240 Fig. 1, Batacera rubus, x J ; Fig. 2, grub of Baiocera rubus, natural size ; Fig. 3, Aeanthopsyche snelleni, natural size ; Fig. 4, iiie Fork- , horned Rhinoceros Beetle {Xylotrupes sp.), natural size ; Fig. 5, a Cockchafer grub, natural size ; Fig. 6, Maechotypa verrucicellis, natural size ; Fig. 7, Lepidiota pinguis, natural size ; Fig. 8, Lecanium nigrum, natural size ; Fig. 9, Lecanium nigrum,, attacked by Cephalo- sparium, natural size ; Fig. 10, Bypocrella Beineckiana, x6 ; Fig, 11, the rubber slug, Mariaella dussumieri, natural size. ix THE KUBBER TREE TEXT FIGUKES PIO. 1. FoTnes lignosus ; mycelium on root, x J . 2. Forties lignosus ; young advancing mycelium and resupiuate fmctifications. x | 3. Brown Root disease ; mycelium on loot, x J ... 4. Uslulina zonata ; black lines in wood, x J ... 5. Ustulina zonata ; black lines and brown areas in wood, x ^ 6. Boot attacked by UUulina zonata, showing black cushions on the exterior, x J 7. Koot attacked by Ustulina zoTuUa, showing Tans of raycclinm between the wood and the bark, x J . . . • 8. Ustwliiia zonata ; fructification, x ^ 9. UstuHiia zonata ; section of fructification, x 6 10. Sphaerostilbe repens ; mycelium on wood of root 11. Sphaerostilbe repens ; details of the fungus 12. Claret-coloured Canker ; cortex pared away to show the discoloured areas 13. Black Thread, an early stage of the disease. Xatural size . 14. Old wound caused by Black Thread, x i 15. Ustulina zonata ; fructification on a .Sewa stem, x^ 16. Kretzsefimaria ; fructification. Natural size 17. Thread Blight on a Hevea stem, x J . 18. White Stem Blight, x J . . 19. Top Canker, x^ . 20. Top Canker. x| 21. Top Canker, x | . 22. Burrs on a Hevea stem 23. Small nodules extracted from burrs. Natural size 24. Plate nodules extracted from burrs, x J 25. A fasciated stem 26. A fasciated stem . . . . 27. Twisted seedlings, eighteen months old. x J 28. Twisted seedlings, one month old. x J 29. Cork warts, x^ . 30. A distorted stem, x J 31. 32. A twisted Sevea stem 33. A lightning scar. x | 34. Diagi-am of cross-section of a lightning scar 35. Small lightning scars on a Hevea stem. x J . 36. Hevea root bored by Batoeera nibus. ^\ ■ 37. Tubes of a bark-eating caterpillar, x | 38. The effect of slugs PAGE 28 32 42 57 58 59 59 60 61 65 70 113 120 123 143 145 155 158 161 161 162 ISl 183 184 190 191 193 193 196 197 198 202 203 203 230 236 247 CHAPTEK I GENERAL SANITATION In olden times diseases of plants were regarded as " visita- tions " and allowed to rage unchecked. In seasons favour- able to their development their ravages caused widespread damage, and, in some instances, the almost total ruin of a country ; and only the advent of less favourable years brought relief. Even after it had been proved that plant diseases were due to the action of specific organisms, and that some steps could be taken to combat them. Little improve- ment resulted at first, because, in the majority of cases, nothing was attempted until the disease had obtained so strong a footing that nothing could be done successfully at any reasonable cost. The fungus of cofEee leaf disease {Hemileia vastatrix) was recognised to be a, very destructive pest in 1869, but it was not until ten years later that active measures were taken against it. There is little doubt that much of this delay was due to a reluctance to admit that any disease existed, and it is only within the present century that public opinion in planting coimtries has come to imder- stand that plant diseases are as inevitable as those of men and animals. This acknowledgement of the inevitability of disease leads immediately to a recognition of the fact that it is necessary to be always on the alert to observe any abnormal or suspicious appearances, and to have inquiry made into them at the earliest possible moment. Speed is an essential factor in the treatment of diseases, and to deal with any one of them successfully it must be attacked in an early stage. In Hevea, at least, this proposition is thoroughly under- stood ; and there is little fear that any disease will be allowed to proceed unchecked or unobserved in Eastern plantations 2 THE RUBBER TREE '^^■ so long as the present vigilance of estate superintendents is maintained. But though the recent advance of public opinion in this respect has been extraordinarily rapid, it stiU falls short of what is absolutely necessary. The continued study of plant diseases has shown what conditions are favourable to their development, and consequentiy what precautions should be observed if they are to be avoided or minimised as far as is humanly possible. In short, such knowledge enables us to advance from the idea of remedial measures to that of preventive measures. It is no longer permissible to adopt systems of planting or methods of cultivation without considering tiieir probable effect when diseases arise, and in the light of our present knowledge that effect can ui many cases be predicted with a close approximation to certainty. The pathologist should be consulted beforehand, not five or six years afterwards when some disease has already appeared ; and in the absence of any such consulta- tion he would fail in his duty if he did not point out how new or old planting practices tended to promote disease. Furthermore, in addition to preventive measures which must date from the opening up of the estate, there are many details of general sanitation which should be attended to if it is desired to keep the trees in a healthy condition. Some of these are indicated in the present chapter. Jungle Stumps By the usual method of clearing jungle land for planting in the tropics all the stumps of the trees are left in situ. That is a fact which agricultural experts and inventors in temperate climates find some difficulty in realising. In temperate countries the trees are felled, and the stumps are afterwards extracted because the land is to be worked by machinery ; but in the tropics machinery is not employed, and therefore this necessity does not exist. " Further, tropical trees, especially on low-lying land or in " rain forest," are often furnished with high buttress roots, and to economise labour they are cut above the latter. Thus, not only are stumps left to decay by natural means, but they are lai^er and more numerous than in temperate coimtries. GENERAL SANITATION 3 The decay of these stumps is brought about by the agency of fungi, the spores of which alight upon the exposed wood and germinate there. The fungus threads (hyphae) attack the wood, and either gradually consume it or else absorb certain parts of it so that the remainder falls into powder. In either case the fungus feeds unseen upon the tissues of the stump, and in due course constructs fructifications of varied form and colour on the exterior of it. The majority .of these fungi are merely saprophytic, i.e. they can live only on dead tissues, but some of them can act as parasites on occasion, and it is the latter which cause trouble. All the root diseases of Hevea, Tea, and Cacao which have been investigated with any approach to completeness have been found to originate, in the most general case, on a neighbour- ing stump ; in some cases it is the stump of a jungle tree, while in others it is the stump of a tree which has been planted for shade and then cut down. The known root diseases of the plants mentioned rarely attack the plant directly, i.e. by the germination of spores upon the plant ; they all require, as a rule, an external base of operations, and this they find in the dead wood of an adjacent stump, or, in some cases, in felled timber. The general plan of attack is as follows : The spores of the fungus are blown on to the exposed wood of the stump, and if the weather conditions are favourable they germinate and their hjrphae grow down into it. These hyphae continue growing in the dead tissues until they have permeated both the stem and the roots, and then they spread from the roots of the stump to the roots of adjacent living trees. Some fungi can only spread to other plants if the roots of the latter are in contact with those of the host stump ; others, however, can spread freely through the soil, drawing food from the supply in the stump which served as a base. Each stump thus affords a centre of disease, spreading destruction in an ever-widening circle. In addition to spreading the disease by means of radiating -fungus hyphae in the soil, each infected stump produces fructifications of the fungus, and these liberate spores which convey infection to other stumps. In some cases fructifica- tions are produced at intervals from shortly after the stump is first attacked until the time when it is completely decayed ; 4 THE RUBBER TREE ''^■ while in the case of other fungi the stump only bears fructifi- cations when it is in the last stages of decay. If there were no dead stumps or fallen timber on Rubber plantations there would be very little root disease. But it is not an easy matter to get rid of these, and whatever method is adopted the cost is high. Still, the fact that root diseases depend on the presence of decaying wood of some kind is generally realised, and it may be said that it is now the exception rather than the rule, at least in Ceylon, to find a Rubber estate which has not cleared up all dead stumps and felled logs. It is important to note that this work has been undertaken, not from a desire to make the estate look clean, but because it has been definitely established beyond any possible doubt that decaying stumps promote root diseases. Of course, under existing conditions, the majority of estates have got rid of their stumps only after disease has made its appearance. It would, however, be foolish if younger estates did not profit by their experience and begin to remove jungle stumps as soon as possible after opening. Owing to the long period which must elapse before any return can be obtained, an estate must be planted up as soon as possible after felling and burning off. Hence, apart from . other reasons, such as loss of soil, etc., it is perhaps too much to expect that the land will be cleared of stumps before the Rubber is planted. Stump - extraction will generally follow planting in ordinary estate routine. But here we are met with an insurmountable difficulty. Any stump-extracting apparatus capable of dealing with jungle^ stumps cannot be employed after the estate has been planted up without causing an enormous amount of damage ; and those which can be used with comparative safety are of very little value. As a rule, inventors of stump-extracting machinery underestimate the difficulty of the problem with which they have to deal, owing to absence of any first-hand acquaintance with local conditions. At the present time^ nothing more can be recommended than digging out the stumps to a depth of two or three feet by manual labour ; and that operation should be begun as soon as the plants are established. Lateral roots should be extracted as far as possible. In the case of a very large stump, with spreading buttress rootsjl I GENERAL SANITATION 5 where the expense of removal is considered prohibitive, a trench should be dug round it, cutting through all the lateral roots. The laterals should be taken out immediately, and the stump itself left until it has decayed to some extent, when it can be removed more easily. The trench should be kept open all the time the stump is left. After the stumps have been dug out they must be burnt. It is unnecessary to point out that this can be done with less risk of damage the younger the Rubber. Thinning out Close planting, with the intention of thinning out in later years, was never widely adopted ; in the majority of cases estates were planted up at the distances it was con- sidered the trees would remain permanently. It needed, however, only the efl&ux of time to demonstrate the truth of the prophecies of mycologists who contended that Hevea could not possibly exist in a healthy condition when planted two hundred to the acre ; and the necessity for thinning out all the earlier-planted Rubber is universally admitted. The arguments for and against close planting are now ancient history, and a detailed recapitulation of them would be merely flogging a dead horse. The points definitely agreed upon are : (1) Close planting leads to poor bark renewal, because the crown of the tree is not large enough to manufacture a sufl&cient quantity of food. (2) The yield falls off, in closely-planted areas, as the trees grow older. The age at which this efiect begins to be evident depends on the rate of growth of the trees ; it has been observed, in the case of trees planted 15 feet apart, at the age of twelve years, in a district at an elevation of 1500 feet, where the growth was comparatively slow, but it has been recorded to occur after the sixth year in the case of Rubber planted 14 feet apart in Malaya. (3) Disease is more prevalent in closely-planted areas. Some of the older Rubber was planted 10 feet by 10 feet, or, in a few instances, 8 feet by 8 feet. In such cases it was permissible to begin thinning out by cutting out alternate rows, as an ample number of trees was left for further thinning 6 THE RUBBER TREE ''^^^ by selection. But in the case of Rubber planted at wider distances originally, thinning should be done by selection throughout, the diseased and weakly trees and the poor yielders beiug removed first. Closely-planted trees "run up." Their lower branches are killed by the dense shade, and their crowns often consist of a few branches directed more or less vertically upwards and bearing comparatively few leaves. The application of manure only increases this effect. The ultimate condition of such trees after thinning is still in doubt. It does not appear probable that they will be able to develop lateral branches lower down, and improvement will, in general, be limited to the existing crown. This, however, refers more particularly to trees planted at 1 2 feet apart or less. Thinning out at the present time is being carried on over any area which bears more than one hundxed trees to the acre, and in the majority of cases the trees have not yet assumed the shape described. Surprise has been expressed that the lower branches of Rubber trees continue to die after a field has been thinned. Apart from any question of disease, this is to be expected to some extent, as, after thinning, the branches which were developed under partial shade are exposed to full sunlight, and this may have an injurious effect, at least for a limited period. Another effect observable after thinning is that the semi- vertical branches are often too" weak to maintain their position, and bend over, sometimes ultimately breaking. Such branches should be cut back before they break. The idea of extracting as much rubber as possible from a tree before taking it out has been generally abandoned. Whenever it is destroyed it will contain some rubber, and when many trees have to be removed, it is better to cut one's losses at the beginning rather than to run the risk of intro- ducing disease by tapping them until they are in a moribund condition. The trees must be uprooted, and all the woody parts removed and burnt. Felling by elephants is a favourite method in Ceylon, and it appears to be, on the whole the most efficient. In this method the surface roots of the tree are usually cut through first, and in some cases the larger branches are lopped in order that the surroimding trees may not be injured by its fall. I GENERAL SANITATION 7 Tlie tap root must be .extracted to a depth of at least two feet. When thinning was first taken in hand, many trees were cut off at ground level, and their stumps have proved just as dangerous as jungle stumps. The root diseases caused by Fomes lignosus, Ustulina, Poria hypo- brunnea, and Brown Root disease, have all been found to develop from the stumps of felled Hevea. Where the lateral roots have been severed these should be pulled up as far as they will come and then cut off ; laterals, two or three inches in diameter, left with their cut ends sticking up above the soil, have developed Ustulina and Poria hypobrunnea. When thinning out was first begun it was anticipated that the development of Botryodiphdia Theobromae on the Hevea logs would lead to extensive outbreaks of Die-back. That has not been realised. On the other hand, Ustulina zonata and Poria hypobrunnea are among the commonest fungi which occur on rotting Hevea logs, while Fomes lamaoensis, the fructification of Brown Root disease, has been found on them on several occasions. It is evident, therefore, that felled Hevea must be removed ; if anything, it is more dangerous than jungle timber. Hevea is now being thinned out to about eighty or one hundred trees to the acre, with acknowledgement that the number must ultimately be still further reduced. What the final number will be cannot yet be decided, but, according to the opinion current at the present time, based on the experience of the last six years, it wUl not exceed sixty. This again brings forward the question what is the most preferable method of planting Hevea in the first instance, and on this point there are two opposed policies. The view most generally held is that the trees should be planted at the distances it is intended they should finally stand. If planted 25 feet by 25 feet, or 30 feet by 20 feet, there will in either case be about seventy trees to the acre, and this would allow for a loss, by disease or otherwise, of ten trees before the number fell below what is at present considered the probable maximum. The objections raised against this plan are — (1) that the loss of soil through wash will be much greater than if the trees were planted closer, and (2) the return in the earlier stages of tapping will be very small. To the first of these it is replied that the wash may 8 THE RUBBER TREE ''^■ be prevented by the use of a suitable cover plaiit, while the relevance of the second has been considerably d iminis hed by the change which has taken place in the genraal view with regard to the size at which Hevea should be brought into tapping. The alternative su^estion is that the trees should or^pi- ally be planted closer, say 20 feet by 15 feet, as in previous planting, and thinned out to half the ntimber, or approxi- mately 20 feet by 30 feet, before the trees bt^ to interfere with one another. In support of this plan, it is urged that there wiU be less wash, that there is a greater number of trees to select from in thiTiniTig out, and that the return would be greater when tapping was first begun. The last of these contentions is the one which usually carries most weight with the planter, though it is questionable whether, under present conditions, it is really as attractive as it seems. Trees are not now brought into tapping as early as they were ; it is realised that, if an estate can afiord it, it is better to wait until the trees are 24 inches in girth at 3 feet than to b^;in to tap them when they are 18 inches, as was previously the case. Again, the trees which are to be thinned out must be removed before the crowns begin to interfere with one another, and, at 15 feet apart, they wiU certainly interfere before they attain the required girtili of 24 inches. The trees should be so far apart at the beginning that they can spread out their crowns without interference and build up a normal framework of branches, not because of any aesthetic ideals, -but because the manu- facture of plant food is carried on by the leaves, and a tree which is subjected to the treatment which Hevea undergoes must be in a position to manufacture food in sufficient quantity to ensure a satisfactory bark renewal. Apart from the above, it is abnost inconceivable that any one should now deliberately adopt a planting method which involves extensive thioning out. The thinning which has been done, it must be emphasised, was never contem- plated ; the trees were planted at the distances it was con- sidered they would stand permanently, and they have been removed because experience has proved that Hevea cannot be grown so close. The full results of thinning out have yet to be realised, but when one considers the cost of the GENERAL SANITATION 9 operations, the dangers of root disease, the loss of trees through scorching, and the general insanitary condition of the estate owing to the previous close planting, it is indeed difficult to imagine that any one would wish to repeat the experience. It is stiU held in some quarters that Hevea may be planted closer on hUl- sides than on the flat, presumably because the slope raises the crown of each tree above that of the tree immediately below it, and thus diminishes the amount of interference between them. But the fact is overlooked that the slope automatically brings the trees nearer together. To take an extreme case, if the slope of the Mil is. 60°, and the trees are planted 20 feet apart along the slope, they are only 10 feet apart horizontally ; if the slope is 30°, they are 17 J feet apart horizontally. If anything, therefore, the trees should be further apart on sloping ground, provided the growth is normal. One has only to examine a field on a steep hUl-side thinned out to less than a hundred trees to the acre to realise this. Intercrops, Cover Plants, etc. In the early days of Rubber planting much discussion centred on the subject of intercrops, i.e. products which could be grown permanently between the lines of Hevea, or which might be grown for the first few years only, so that some revenue might be obtained before the Rubber came into bearing. Practical applications of the schemes then advised have not been numerous ; as a rule, Rubber estates have- grown rubber only, though in Ceylon Cacao was inter- planted in a few cases, and in Malaya and Java Cassava or Coffee. In Ceylon interplanting has usually meant the planting of Hevea through existing Tea or Cacao. This is not strictly interplanting, but a gradual replacement of the previous product by Rubber, and the method was dictated by necessity, not by choice. Perhaps it was at first expected that the two products would flourish side by side, but experience has proved that, as a rule, when the Rubber has grown up, one of them must be removed. In general^ ^t may be said that the rubber planter has 10 THE RUBBER TREE ''^ concluded that intercrops are not worth the trouble from the financial point of view. They have also been recom- mended on the ground that they will hinder the spread of disease ; but, as advised or practised hitherto, intercrops have tended rather to promote the spread of disease than otherwise. From a purely mycological standpoint there are two points to be considered when selecting an intercrop or a cover plant for Rubber, viz. its effect on the generaii hygienic conditions of the estate, and the diseases to which it is liable. It is admittedly wrong to select a plant which is subject to the same diseases as Hevea, and it is also inadvisable to choose one which wiU grow so tall and dense that the bottom shade and consequent humidity are thereby unduly increased. An intercrop which would grow no higher than Tea is usually allowed to grow would be ideal, while a cover plant should, if possible, be lower stUl. Cacao has proved quite unsuitable as an intercrop for Hevea. When established, the shade and humidity in the mixed plantation are greater than if Hevea had been planted throughout instead of Cacao, and consequently the general sanitary condition of the whole estate is lowered. In addition to that, the diseases of the two plants are in many cases identical. Brown Root disease and Fomes lignosus attack both Hevea and Cacao ; Botryodiphdia Theobromae causes Die-back both in Hevea and Cacao, and is abimdant on decay- ing Cacao pods ; and PhytopMhora Faheri, which is the cause of Cacao pod disease and canker, similarly produces pod disease and canker in Hevea. But the cMef trouble from Cacao arises when the Cacao is cut out. If it is simply cut off at ground level, as has been done in many cases, the stumps frequently develop Ustulina, Fomes lignosus, or Fomes h/maoensis, which spread to and cause root disease in the surrounding Rubber trees. Of these, Fom^es lamxwensis (Brown Root disease) is the most common, and several instances have occurred in which large areas under Hevea were permeated with Brown Root disease, owing to the development of this fungus on Cacao stumps. When Cacao is removed from a mixed Hevea and Cacao estate, it must be uprooted. Taking all things into consideration, it must be concluded that, from a mycological point 'of view. Cacao I GENERAL SANITATION II is the worst possible intercrop which could be chosen to plant among Hevea. Coffee has been interplanted on several estates in Malaya and Java, and a few in Ceylon. The diseases which Coffee shares with Hevea are Fomes Ugnosus, Brown Root disease {Fomes lamaoensis), Pink disease, and Thread Blight. Pink disease is likely to be prevalent if the coffee is thickly planted. Tea was never interplanted at the same time as the Hevea, but the latter was planted through old Tea in Ceylon over large areas. In course of time the Tea ceased to be remunerative, owing to the shade and root competition of the Hevea, and was either taken out or allowed to die out. In the latter case, or when the Tea was simply cut off at ground level, extensive developments of root disease have followed. In 1910 it was known that the Hevea might be attacked by Ustulina zonata, which is the cause of the commonest root disease of Tea in Ceylon, but since then it has been found that the root disease of Hevea which most usually spreads from decaying Tea stumps is that caused by Fomes Ugnosus, and the worst outbreaks of the latter disease in Ceylon have occurred on old Tea fields where the tea was cut down at ground level. As the converse of the above, it may be recorded that on estates at medium elevations in Ceylon, where it has been decided to keep the Tea and cut out the Rubber from mixed fields, leaving the Rubber stumps has resulted in the death of large numbers of the surrounding Tea bushes through the root disease caused by Botryodiplodia Theobromae, which has spread to the Tea from the decajring Rubber stumps. Kapok stumps (Eriodendron anfractuosum) among Hevea have been found to give rise to Brown Root disease. Where cover plants or green manure plants have been adopted Crotalaria striata has been largely employed. This is generally sown thickly, and in most cases it does not grow higher than 3 feet. It suffers from two leaf diseases, but neither of these is likely to attack Hevea. One of these, which takes the form of circular, dry, brown spots, often concentrically zoned, is caused by Sphaerella Crotalariae. The other is caused by Parodiella perisporioides, a well-known parasite of leguminous plants in the tropics ; the fungus forms minute black points, scattered over the upper surface 12 THE RUBBER TREE «=^^ of the leaf, but the leaf is not kUled— it simply curls up. This latter disease is most prevalent on old Crotalarm, after it has been cut back, and on self-sown plants. There is, however, a danger in Crotalaria in some districts, where it grows much taller and stouter than it does in Ceylon, e.g. in some parts of Southern India. In these localities it may grow to a height of 9 feet in a year, without flowering, and may acquire a woody stem about an iuch in diameter: such plants are attacked by Pink disease {Corticiwm salmoni- color), and the disease soon spreads to the Hevea. There is no danger in growing Crotalaria among Hevea in most coimtries ; and where the growth is so vigorous that it forms a tall jungle, some smaller green manure and cover plant must be adopted, or the Crotalaria must be cut down earlier. Another species of Crotala/ria {Crotalaria fulva) has been foimd to be subject to the attack of Poria hypobrunnea. Tephrosia Candida has been largely planted as a green manure crop during recent years. When it is old, and the stem has become thick and woody, it is sometimes attacked by the root disease caused by Poria hypobrunnea. It would appear that this does not occur, in the low country of Ceylon, until the plant is over two years old, and has been repeatedly lopped. Consequently a time limit of about two years should be set to the growth of Tephrosia Candida, and at the expiration of that time the old stumps should be uprooted and burnt. Any green manure plant which grows tall should not be planted in dense masses ; the lower the plant the less is the danger of disease. A plant which did not exceed a foot in height would be ideal, and could be sown as thickly as desired. There is often a tendency to let green manure plants run too long. In temperate climates, such a crop is often ploughed in at the end of a month ; but in the tropics the idea usually appears to be to make it run as long as possible, and to obtain some profit by selling seed. There is little advantage in a green manure plant as such until it is cut down and mulched in. Alhizzia moluccana, planted through Hevea for green manuring, and subsequently felled, has been found to give rise to the root disease caused by Ustulina zonata. The GENERAL SANITATION 13 fungus develops on the Alhizzia stumps and travels along tiie lateral roots to any Hevea roots which, happen to be in contact with them. Alhizzia stumps must be dug out. The thorny dadap, or Bois Immortelle {Erythrina umbrosa), after being felled has been known to develop Forms lignosus in abundance on its stumps and fallen logs. In the worst case the trees were about thirty years old, and had originally been planted as shade for Cacao. Hevea was subsequently planted through the Cacao, and some years later the Erythrina was ringed. The development of Fomes lignosus became apparent at the time the ringed trunks fell over. Fomes lignosus has also been found to occur on the smooth dadap {Erythrina lithosperma), and to kill out old trees. The root diseases of Hevea, which are known to spread to the rubber tree from the stumps of cultivated plants, may be enumerated as follows : Brown Root disease, from stumps of Hevea, Cacao, Ceara Rubber, Kapok, Grevillea. Ustulina zonata, from stumps of Hevea, Tea, Cacao, Alhizzia. Fomes lignosus, from stumps of Hevea, Tea, Cacao, Jak, Bois Immortelle, and Dadap. Poria hypobrunnea, from stumps of Hevea and Tephrosia Candida. It is evident that when an intercrop has ceased to be remunerative and it is desired to remove it, or when a green manure plant is to be dispensed with, it should be removed completely, not allowed to die out and decay in situ. More- over it is not sufficient merely to cut the plant down ; the stumps must be extracted as well. All the available evidence points to the conclusion that no stumps of any kind can be left among Hevea without incurring the risk of serious losses through root disease. PRUNmG On many estates lateral branches which arose from the lowest six feet or so of the stem have been pruned off ; or when trees forked near ground level one stem has been removed. In the majority of cases the branch or stem has been sawn across a few inches from the main stem, thus 14 THE RUBBER TREE ''^^^ leaving a " stub " two or three inches long. This was the method recommended years ago, before the principles of plant physiology were applied to garden practice. It is now generally recognised that the bark will never grow over such a stub, and that the end always remains exposed and affords a point of entry for destructive fungi. In Hevea the stub generally dies back. The current of water and food passes up and down the main stem, and the stub is side-tracked. When the stub is dead the bark and wood of the stem grow round it and encircle it with a collar of new tissue ; and when the stub decays and falls out, a cup is left, in which rain-water collects, with the result that a rot extends into the wood of the main stem. Branches should be pruned off in such a way that the wound will be healed rapidly by the growth of new bark over it, and the modern pruner obtains the desired efEect by cutting off the branch as close to the main stem as possible. The cut should be made parallel to the main stem and close to it ; it should not be made perpendicular to the branch which is cut ofi. According to the old idea the cut should be made so as not to injure the bulge at the base of the branch ; the modern pruner cuts right through the bulge, and endeavours to leave the stem as smooth as possible, i.e. without any projecting remains of the branch. He certainly makes a bigger wound, but as the bark has only to grow on in a straight line, it heals over completely in a comparatively short time. Pruning ofi large branches should never be done by a single operation. If they are sawn ofi close to the stem the branch falls when partly cut through, and usually tears off part of the stem. The first cut should be made about a foot away from the stem, on the under side of the branch, and continued about half-way through it. A second cut should then be made two or three inches farther away from the stem, on the upper surface, and this should be continued until the branch is severed. Finally the stub should be sawn ofi flush with the stem. It is necessary to have a gang of coolies on a Rubber estate trained to remove dead branches and to prune where it is considered necessary ; they should be taught the difierence between pruning trees and chopping firewood, and should be provided with proper tools. At least once a year a complete I GENERAL SANITATION 15 round of the estate should be made, and all dead and broken branches pruned off. The Protection op Wounds Wounds made by pruning ofi large branches, or by lopping trees to get rid of Pink disease, or by excising extensive areas of cortex attacked by canl^er, must be protected in some way or other to prevent the entrance of fungi into the tree through the exposed wood. If the wounds are large, so that new bark cannot be expected to grow over it for some years, the wood, if left unprotected, will gradually decay, and large cavities may be formed. Coal tar is the best substance to employ for covering wounds. Stockholm tar has been found to cause more damage than coal tar in all the recorded experiments, and from a mycological point of view it is too evanescent. The tar shoiild be applied cold, so that it does not run unduly over the surrounding bark, but, in the case of Hevea, no appreciable damage is caused if the tar happens to be applied to the bark round a wound. Where it is found that coal tar does not stop the entrance of borers, the wood should first be painted with Solignum, or BrunoKnum, and tarred when that is dry. White lead paint is extensively used in orchard practice for protecting pruning cuts. Experiments have shown that the cowdung and clay mixture which has been so long in use in the tropics is not as effective in promoting the rapid healing of a woimd as was supposed. Even in ^e case of renewing bark the thickness of the renewal beneath the mixture is not greater than on untreated surfaces in the same time. Large wounds should not be covered with cowdung and clay, as the mixture does not prevent the entrance of bprers, and it favours the decay of the wood. The only noticeable effect of cowdung and clay is that it keeps the stem moist. This can readily be seen in fairly dry weather when the stem of the tree is dry ; if the mixtiire is then scraped ofE, the part covered by it will be found to be damp. On the majority of Eubber estates this is a disadvantage, but on estates in drier districts at a high elevation the appKcation of cowdung and clay, by keeping 16 THE RUBBER TREE the stem damp, might prevent splitting of the renewing bark in the dry weather. It should not, however, be apphed if any bark diseases are present. Scraping In the early attempts at rubber tapping, when the latex was allowed to" run over the surface of the stem down to the base, it was recommended that the tree should be carefully and hghtly shaved to obtain a perfectly smooth surface. This is no longer necessary, now that the latex is conducted to the collecting cup by a vertical channel, but the practice is stiU kept up on some estates, more with the idea of making the trees look tidy. It is now called " grooming " the trees. There does not appear to be anything gained by this process, and in many cases it is distinctly dangerous. The outer corky bark is the natural protective tissue of the tree, and if it is scraped ofi the underlying cortex is exposed to the attacks of fungi until it has formed a new cork layer. In dry districts the new bark layer may take the form of thick scales. Serious attacks of Brown Bast have been known to follow this scraping, especially when the green layer of the cortex has been cut into. It is generally agreed that it is wrong to cut into the green, but in the majorify of cases the cooly does, if he is given a knife. It is certainly necessary to remove loose bark scales, and ia the wetter districts it may be advisable to brush ofi the spongy layer on very corky-barked trees, but nothing should be removed which cannot be brushed ofi. For that purpose a piece of coir might be used, not a solid piece of coconut husk. Wire brushes should certainly not be used. In Java it is said that Brown Bast may arise from super- ficial bark wounds, and, in consequence, it is recommended that the outer corky layer should not be scraped off, nor should patches above the tapping surface be smoothed, in order to inscribe data concerning the tapping, etc. In experiments carried out by Sharpies in the Federated Malay States, trees heavily scraped, the green layer being removed, were in several instances attacked by borers, while in one case this occurred on a tree lightly scraped, i.e. one on GENERAL SANITATION 17 wMoli the green layer was left intact. The unscraped control trees were not attacked. It is sometimes necessary to scrape trees, at least locally, to determine whether they are attacked by a bark disease, but gratuitous scraping should be avoided. Forking In some countries Eubber estates are periodically forked, or dug over, either in the course of manuring or applying lime, or as an independent method of cultivation. In Ceylon it is generally held that Rubber which is cultivated in that way responds by showing improvement both in growth and yield. In other countries this has been disputed, and it has been alleged that such treatment is not only useless, but dangerous, as it may give rise to root diseases. It is open to discussion whether it is advisable to apply horticultural methods to the cultivation of a forest tree. The effect of forking, carried out periodically for a number of years, would appear to be a suitable subject for investigation by an Experiment Station. When Hevea attains a tappable age the ground is usually permeated with roots. The large laterals spread out from the base of the stem and branch repeatedly untU they termiaate in masses of fine white rootlets. In general the roots rim not far below the surface. Consequently, in forking, large numbers of the smaller roots are broken. As the Rubber grows older the main roots increase in thickness, and thicker roots will be met with further from the stem. The question then arises whether the fungus of a root disease, e.g. Ustulina, will attack the tree via the damaged or broken roots. From a general knowledge of the habits of Ustulina, it would not appear probable that that particular fungus would attack the smaller damaged roots, up to, say, one-eighth of an inch in diameter, but it is quite ifl^ely that it would attack the larger roots if these are. in any way damaged or wounded. Hence it is advisable in forking young Rubber to keep well away from the base of the trees, and to increase the distance as the trees grow older. In old Rubber, forking, from a mycdlogical standpoint, is not to be recommended. Up to the present no cases of root disease have been 18 THE RUBBER TREE °^^- traced to injuries inflicted during forking. One effect has, however, been observed to follow frequent forking under certain conditions, viz. a general die-back of the ends of the branches over the whole of the crown of the tree. This occurred in the case of backward trees on poor quartzy soil. In such cases too frequent disturbance of the roots may produce an effect which simulates the early stages of a root disease. Tree Surgery Hitherto Rubber estates have usually carried too many trees to the acre, and consequently the removal of some of them through disease has been regarded as not involving any considerable loss. But when estates have been thinned down, probably to sixty trees to the acre, each tree wiU be proportionately more valuable, and it will be necessary to take all possible steps to preserve them. In the past the simple and easy plan of cutting out diseased trees could be adopted without any hesitation, but that cannot be carried on indefinitely, and the fewer trees there are the greater the efforts which must be made to keep them. It wfll then become a question of individual treatment in order to pro- long the life of each tree to the fullest extent. A somewhat similar problem has arisen in connection with the trees in gardens and public parks in large towns. Many of these trees were planted when the towns were small, and they cannot now be replaced because very few trees would come to maturity under the surroimding condi- tions. Hence, as far as can be done, endeavours are directed towards retaining the existing trees as long as possible, and in consequence there has been developed an art of tree surgery, or tree repair, several of the methods of which coi:dd be usefully applied to Hevea. The practice which, it would appear, could be most profitably employed in the case of Hevea is that of filling up cavities in the stem. Such cavities may result in the upper part of the stem from improper pruning, or from wounds caused by branches being wrenched off by the wind, and at the base of the stem from a collar rot caused by canker or root disease. But whatever the cause, such cavities are gradually enlarged by the action of wood-rottiBg GENERAL SANITATION 19 fungi, until the stem breaks off or the tree is hollowed out and falls. The idea of filling tree cavities is not a new one, but it is only comparatively recently that methods have been adopted which are likely to prove successful. Stopping tree cavities is analogous to dentistry, and two cardinal principles must be observed, viz. all decayed tissue must be cut away, and the filling must completely fill the hole, so that water cannot lodge behind it or fungus spores and insects obtain an entrance. It is doubtful whether this method can be advantageously applied, in the case of Hevea, to large cavities in the upper parts of the tree. The wood of Hevea is brittle, and the excision of all the decayed tissue would probably weaken the stem to such an extent that it would break off. On the other hand, if such cavities are not treated, the stem wiU ultimately break ofi owing to the progress of the decay. In this respect prevention is better than cure ; and more attention should be given to correct pruning and periodic tarring of wounds. Cavities at the base of the tree, however, could safely be treated. All the diseased wood must be cut out ; other- wise the fungi will continue to destroy the wood behind the filling. Successful treatment depends chiefly on the thorough- ness with which the diseased wood is removed. It should then be painted with a coat of white lead paint and after- wards be filled solid. Creosote or Brunolinum, etc., followed by a coat of tar may be used instead of white lead paint. Various mixtures are used for the filling. Bricks, stones, and cement is the most usual, the cement being mixed with two parts of fine sand. There should be no spaces left between the filling and the wood, and the outer face of the filling must be finished ofi smooth with the cement. The bricks and stones merely add bulk to the material : the lining next the wood should be cement, and the bricks, stones, etc., embedded in the middle of the cavity. After the filling has set it is left for a day or two, and then covered with coal tar to prevent cracking. The filling must not be brought level with the outer bark of the tree. What is desired is that the callus from the edges of the wound should grow over the cement, and either cover it completely or at least cover it 20 THE RUBBER TREE ^^ ^ at the edges so that it holds it in position. Hence the filling should only be brought to the level of the cambium. In the case of cavities in branches in which rain-water collects, care must be taken to see that they are quite dry before filling is attempted. If they are very deep, an auger hole should be bored into the branch to reach the base of the cavity so that any water will drain out. On branches which are liable to bend and sway in the wind, a cement filling may crack and fall out. In such situations a mixture of asphalt and sawdust is used, iu the proportion of one part of asphalt to four parts of dry sawdust. The sawdust should be from hard wood. The mixture is prepared by stirring the sawdust into boiling asphalt, and it is appUed before it has cooled. Cleaning up Forks The bark at the main forks of Hevea usually becomes cracked arid scaly. This is in part due to the increase in thickness of the tree and the mutual interference of the branches, and it may be assisted by the movement of the stems by the wind, and the flow of rain-water over the fork. The phenomenon is not a sign of disease in the cases hitherto recorded, and it is not in itself injurious, but the loose bark scales may afEord a point of entry for a fungus. UstuUna zonata frequently attacks Hevea at a fork, and it is probable that its attack is facilitated by the presence of these loose scales. A periodic cleaning up of these forks is practised on several estates, and it is especially to be advised where UstuUna is prevalent. The loose scales should be brushed off, and the fork painted with tar, or a mixture of tar and tallow. The latter is the more permanent, as the bark which is simply tarred scales off earlier ; but it is a matter for decision on the estate whether it is cheaper to use tallow or to renew the tar when necessary. CHAPTER II ROOT DISEASES When the roots of a tree are attacked by a fungus they are no longer able to perform their proper functions, and con- sequently the supply of water to the stem and leaves is cut ofE. The symptoms of a root disease are, therefore, purely secondary in the majority of cases, for" it seldom happens except on large trees that the fungus has advanced above ground by the time the tree is dead, and the upper parts die from lack of water, not from an attack of the fungus on those parts. It follows that the symptoms of all root diseases are more or less the same, and especially on yoimg trees are such as might be expected to follow if the trees were subjected to a prolonged drought. If the tree is a small one the leaves suddenly turn brown and dry up, and the tree usually dies with most of its leaves still attached ; at the same time, the cortex dries and no latex exudes if it is cut. Large trees may exhibit different symptoms at the beginning of an attack, though the final stages are generally the same. Part of the foliage may fall off while still green, months before the tree dies ; this occurs especially m wet weather. Or the smaller branches may die back gradually, all over the crown, or especially in the upper parts, so that the tree becomes stag-headed. But ia some cases the tree shows no signs of disease imtil it dies suddenly, or is blown over. The difference between the effect on old and young trees respectively depends in general upon the extent to which the lateral roots have developed. Death is usually sudden in the case of young trees which have not acquired large lateral roots, but where the latter are present the tap root may be completely destroyed without any evident ill effect 21 22 THE RUBBER TREE «=^^ upon the tree, and it is in these cases that, the tree often shows no indication of disease until it is blown over. When trees are blown down root disease should always be suspected. The differences in old trees depend also on whether the laterals or the tap root is first attacked. A sudden fall of leaves, dying back of small branches, and cessation of the flow of latex are often early -indications of an attack of root disease on the laterals. These preliminary symptoms are rarer when the tap root is attacked, because the laterals are then still able to nourish the tree until the fungus reaches them in turn at the collar. But before that happens the tree in many cases falls in a moderate wind. In the root diseases caused by TJstulina and Fomes lamaoensis, the first evident efiect is in many cases a coUar rot, i.e. the production of an area of decayed bark at the collar on one side of the stem, with a corresponding region of diseased wood behind it. This results from an attack of the fungus along a- single lateral root. The fungus travels along the root to the stem, and there attacks the bark and wood immediately round the point of origin of the root. . As both these diseases progress rather slowly, this rot may be well advanced before any effect is observable in the crown. Except in young trees, the effect of a root disease op the flow of latex is highly variable. In the case of Fomes lignosus, cessation of the latex flow has been known to result from an attack on the laterals, eight months before the tree was evidently dying. On the other hand, when the tap root has been destroyed, trees have yielded latex imtil they were blown down. In the root disease caused by TJstulina, it has frequently been noted that the trees attacked yielded an abnormally large quantity of latex for some > weeks just before they succumbed. These difierences are of the greatest interest, especially in view of the theory that the roots constitute a reservoir of latex, and further observations on this poiat are desirable. Root diseases of Rubber are sometimes divided into Wet Rots and Dry Rots, according to the character of the diseased wood ; but while this classification may be feasible in some countries, it is likely to prove misleading if transferred to others. In Malaya the term " Wet Rot " is applied to the rot caused by Forms pseudo-ferreus, but in Ceylon the ROOT DISEASES 23 wettest rot is usually that caused by Fomes lignosus. Brown Root disease may be either a wet or a dry rot according to external conditions. Similarly, the term " Heart Rot," signifying that the fungus attacks the heart wood in preference to the sap wood, cannot be confined to any particular disease. On underground roots, the known root disease fimgi usually attack the whole root ; but when the fungus advances upwards it frequently travels up the stem more rapidly in the heart wood, and causes a conical decayed or diseased region. This occurs quite commonly in Brown Root disease and Vstv^- lina, and it is not uncommon in the case of Fomes lignosus. For several years it has been customary at Peradeniya to develop the fungus, whenever possible, from any llevea roots which present any feature varjong from the typical characters of the known root diseases. One frequent phenomenon iu diseased roots is the occurrence of a broad, rusty-coloured zone in the wood bordering on the decayed region. For example, when a root which ran along the surface of the ground has been attacked on the lower side, it. is often hollowed out half-way through from below, and the decayed region may be bordered above by the zone de- ^ scribed. Or it may occur iu a stem when the rot is advancing upwards. In some cases such specimens have produced Fomes lignosus, in others, Ustulina. Hence the discolora- tion is not typical of any one disease. In general there is little hope of saving a tree which is attacked by a root disease. At least in the majority of cases, the first tree discovered at any centre of disease is usually beyond recovery. But trees may be detected in an early stage of the disease round a dead tree, or round a known disease patch, and these may constitute exceptions to the general rule. The treatment of root diseases involves the removal of aU dead trees, decaying stumps, and timber in the affected patch, the isolation of the patch by means of a deep trench, and the application of lime to the soil. It is now generally recognised that decaying stumps and timber are the source of root diseases in general, and it is of little use to dig out and' burn the dead tree and leave the stump from which, the fungus has spread. 24 THE RUBBER TREE ™^ The first operation should be the removal of the dead tree. This should be cut down if it has not abeady fallen, and as much as possible of the roots dug out. The laterals should be followed up and dug out, especially if they are diseased. Neglect to follow up the laterals is one of the chief causes of failure in treating root diseases. Any piece of a diseased lateral is capable of communicating the disease to a healthy root which happens to come in contact with it. The upper parts of the tree can be taken for firewood, but the diseased roots, and any neighbouring jungle stump, or decaying logs, should be burnt on the spot.' The afEected patch should then be forked over, and all pieces of dead wood collected and burnt. The object of trenching is to isolate the patch which is known to contain the mycelium of the fimgus, and to sever all communication between the roots in that patch and the roots of surrounding trees, so that the ftmgus cannot spread outwards along the roots over a wider area. The position of the trench is consequently governed by the distance to which the diseased laterals extend. In any case, the trench should enclose not only the diseased tree, but also a complete ring of the surrounding trees, even though the latter are apparently healthy. Having decided upon the position of the trench, the ground should then be limed before the trench is cut. The majority of fungi prefer an acid medium. Hence the application of lime, which makes the soil less acid, produces a condition which is less favourable to fimgus growth. In Ceylon it is usual to apply lime to root disease patches at the rate of sixty pounds for each dead tree or stump, Avith the addition of fifteen pounds for each living tree which is to be enclosed within the trench. In Malaya, twenty-five pounds for every hundred square feet is recommended. The linie is to be scattered over the afEected patch, not merely in the trench, and special care should be taken to see that it is applied liberally along the lines of the lateral roots. As it is desired to apply the lime to the soil in which the fungus grew, it is bettet to make the application before the trench is dug, otherwise one is in a great measure merely liming the excavated soil, especially if the patch is a small one. Aitef the lime has been scattered over the soil, it should be forked in. ROOT DISEASES 25 The depth of the trench should, as a rule, be about two feet, but in some soils it may have to be more. The trench should sever all lateral roots, and though in general this is effected by the depth stated, I have seen instances in deep, loa,my soil, where the lateral roots of a jak tree, one of the worst sources of Fomes Ugnosus, ran horizontally at a depth of three feet. The quantity of soil to be disposed of is, how- ever, so large when the trenches are deep, that they should not be carried down to a depth of three feet unless that is absolutely necessary. The soil dug out is thrown inwards on the affected patch, not on the outer edge of the trench. Where the mycelium occurs on the under side of stones of moderate size, these should be turned over so as to expose it to the sun and sprinkled with lime. It is now becoming customary to open up and examine the roots of the trees which are included within the isolation trench, in order to determine whether they have already been attacked. It is of coilrse impossible to follow up the roots to their extremities, but enough can be done to show whether the tree is seriously affected. The roots should be exposed for a radius of about three feet from the stem, and the tap root to a depth of about two feet. The operation requires great care, especially in rocky soil where large stones are wedged between the roots. Indeed, the examination in such cases often causes so much damage that its value is doubtful. Any attempt to use the root as a fulcrum to lever out stones generally results in breaking away large areas of cortex. In one case where this examination was carried out over an area of a hundred acres, infested with Fomes lignosus, it was found that a cooly could not open up more than two trees per day, if excessive injury was to be avoided. All wounds caused should be tarred. If upon examination the tap root is found to be decayed, the tree should be removed . If the fungus is found advancing towards the collar on one or two laterals, these may be cut back into soimd tissue, and the diseased laterals dug out. It must be borne in mind that the mycelium usually travels along the under side of the laterals, especially when the upper side is exposed ; this is particularly so in the case of Fomes lignosus. In the latter disease, the external strands of mycelium fairly frequently extend over the surface of the 26 THE RUBBER TREE ^^^^ root in advance of the penetration of the fungus. The part covered by the youngest mycelium may consequently not have been attacked, or only attacked to a slight depth. In such cases, the mycelium and any underlying decayed bark and wood may be cut away and the wound treated. This method is especially useful when the tap root only has just been attacked. In Ceylon it is usual to dress the roots from which mycelium has been scraped ofi with Brunolinum, or tar, while in the Straits Settlements, Bordeaux paste has been used. It must be remembered that the mycelium travels inside the root as well as on its surface, and consequently, if the decayed parts of the root are not cut away, any treatment is useless. The method is said to have been attended with great success, trees which bore the mycelium of Fow£s lignosm having been completely cured. There is, however, probably an element of doubt in some instances, owing to the possibility of a mistake in the identification of the mycehum. Loose, white, or bluish-white niycelium is fairly plentiful in soils which contain dead leaves, twigs, etc., as is usually the case on a Rubber plantation, and in general this is merely saprophytic. Such mycelium is frequently found in the soil round the base of a Rubber tree, and is often mistaken for that of Fames lignosus. In identifying Fames lignosus, only the stout mycelium adherent to the root can be relied on. The foregoing method is likely to be of service in cases of Brown Root disease and Ustulina, since, where these diseases are known to be prevalent, many cases can be discovered when only one lateral root has been attacked. Both these diseases progress comparatively slowly, and even when the fungus has penetrated into the stem round the lateral root, it may yet be possible to save the tree by cutting away all dead wood. The cavity should then be tarred and filled up with concrete (see p. 19). The holes round the trees examined may be left open for a week or two in fine weather, but if there is any danger of water collecting in them they should be filled up as soon as possible. Where cavities have been filled with concrete, the filling should where possible be left exposed ; this could be done on a hill-side, where a channel could be cut so that water might drain off, but on level land the earth should be levelled up 80 that water will not lodge against the filling. ROOT DISEASES 27 Over areas wMcli are known to be more or less generally infected with a root disease fungus, sucli as old Cacao land where Brown Root disease is spreading from the Cacao stumps, old Tea areas where Fomes lignosus is developing on the abandoned Tea, and other similar cases, the whole area should be limed at the rate of at least a ton per acre, after the removal of the decaying stumps of the previous cultivation or intercrop. Six root diseases of Hevea have been recorded up to the present. These may be distinguished in most cases by the following characteristics : I White, or yellowisli, or reddish strands on the exterior of the root . Red smooth strands, or red sheets, which become black : with red or brown lines in the wood .... Fomes lignosus. Sand and stones cemented to the root by fine tawny-brown mycelium : brown lines in the wood .... Inner bark decayed and collapsed, so that the outer bark is easUy removed ; frequently (not always) a tough skin- like dark brownish-red mycelium bound up with the outer cork layers of the bark ..... No external mycelimn, or with a few black projecting points : white fans of mycelium between the bark and wood : black lines in the wood No external mycelium : red or black strands between the bark and the wood ...... Poria hypohrunnea (Red Root disease). Fomes lamaoensis (Brown Root disease). Fomes pseudo-ferreus. Ustulina zonata. SpJiaerostilbe repens. Fomes lignosus, Klotzsch {Fames semitostus, Auctt., non Berk.) This disease is the most widely-known root 'disease of Hevea, partly because it was the first to be discovered, but principally because of the serious loss it has caused in many locaKties. It was originally recorded under the nanie of Fomes semitostus, and in most of the literature relating to it that name has been employed, but it has since been found that 28 THE RUBBER TREE CHAP. the original Forms semitostus is quite a different fungus, and that the correct name of the species which causes this Rubber root disease is Forms lignosus. The disease was first discovered by Ridley at Singapore in 1904, hx Ceylon it was first recorded in 1905, The absence of any previous record in Ceylon is doubtless due' to the fact that much of the earlier Ceylon Rubber was planted among Tea or Cacao, and that some of the earhest plantations were established on land which had been cleared of almost all the jungle stumps prior to planting. Since 1905 this disease has been found to be fairly general in the Ceylon Rubber districts, and there are few estates which cannot show a Fomes patch ; while in some cases it has caused considerable loss of trees and a large expenditure on methods of treatment. In Malaya it is known as the commonest root disease of Hevea, and large sums have been spent on its eradication. It occurs in South India, Java, Sumatra , and Borneo, and in West Africa and the Congo region. The disease does not appear to have been recorded from the Western Hemi- sphere, but as the fungus is known to occur throughout the tropics, it will no doubt ultimately be found to attack Hevea wherever it is grown. As a rule this disease is readily iden- tified by the mycelium on the exterior of the roots. This takes the form of stout smooth cords firmly attached . . to the bark, running more or less longitudinally along the root, and uniting here and there to form a network (Pig. 1 ; Plate II., Fig. 4). These cords Fio. 1. — Fomea lignosus ; mycelium on root, x J. ROOT DISEASES 29 may be white, or yellowish-white, or reddish. They vary in breadth up to a quarter of an inch, and may spread out here and there and unite into continuous sheets. In general they are more or less rounded on the upper side, and conse- quently stand up above the level of the bark. The younger growing parts are white and soft, and often branch in a radiating or fan-like manner (Fig. 2). Such immature cords are often found at the collar. It is rare that the mycelium extends up the stem above ground. When it does the strands usually divide into finer threads, or separate hyphae, which can only be detected with difficulty among the rough bark at the base of the stem. This, however, in general, only occurs when the tap root has been almost completely destroyed. On trees in normal situations, the depth of the tap root which is covered by the mycelium may be as much as thirty inches, but where a tree is growing near a bank, or by the side of a deep drain, it may be much greater. The external mycelium gives rise to threads which penetrate into the tissues of the root and bring about their decay ; and the whole of the wood and cortex is ultimately permeated with fine fungus threads which render them, soft and friable. The type of rot varies, but in Ceylon the decayed wood is very often wet and sodden. It is not notably discoloured, and the bark has the normal brown colour of dead bark internally. A different appearance has been observed on several occasions in Ceylon, usually in the drier districts. In these cases the tap root did not show any external strands, but appeared blackish and sodden, and on removing the bark the wood was found to be decayed and watery, with, short white lines of mycelium embedded in the surface. The fructifica- tion was subsequently developed from the diseased tap root and the identity of the disease •determined. The lateral roots often bore the normal cords of mycelium, and it would appear that in these cases the fungus, after attacking the tree via a lateral root, proceeds down only inside the tap root. In general the fructification of the fungus will seldom be found on trees which have been killed by this disease ; it can only be formed above ground, and as a rule the mycelium has not reached the surface by the time the tree is dead or has been blown over. Exceptions to this rule may occur in the 30 THE RUBBER TREE ohap. case of trees growing on land which is subject to periodic inundation, and I have seen the fructification at the base of a Hevea, not yet dead, which happened to be growing, neglected, in a patch of scrub. Possibly the production of fructifications before the tree is dead may become more general when older trees are attacked. Of course, if a dead tree is left standing for some months, the fructification will ultimately develop at the base unless prevented by white ants ; and if a fallen tree killed by Fomes lignosus is allowed to lie and decay, the fructification will similarly be developed along its whole length. But under ordinary estate conditions, where a diseased tree is discovered before, or as soon as it has died, neither the stem nor the root will show any sign of a fructification, at least in the case of trees up to twelve years old. In new clearings and young plantations, it is usually possible to find the fructification of the fungus on a decaying jungle stump near the trees attacked, and this continues to be the case as long as the stumps remain. Where Hevea has been felled in thinning out, and the stumps left, the fructification may be found on the latter, and the same holds good for Cacao stumps. Iij fact, in the most general case, the disease spreads to the Rubber from a decaying stump of some kind, and the fructification is usually present on the stump from which the disease originated. The fructification (Plate I. ; Plate II., Fig. 1) first appears as a small orange-yellow cushion. This grows out horizon- tally into a flat plate, more or less semicircular m outline,' attached to the stump along its hinder margin. In general, this plate is up to four inches in diameter, but in favourable situations it may be as much as a foot. It is about half an inch thick behind, and thins out regularly towards the margin. From their shape fungi of this class are known as bracket fungi : many species occur quite commonly on decaying logs and stumps, but the majority of them are harmless. - Fomes lignosus is identified by its colour, but the coloiu: varies enormously according to the age of the fungus and the amount of moisture in it. At first the bracket is a rich red- brown on the upper surface, with a bright yellow margin, while its lower surface is bright orange. If it dries in that stage, the red-brown colour of the upper surface gradually ROOT DISEASES 31 disappears, not uniformly all over, but in concentric zones, so that it becomes banded witli broad alternate zones of red- brown and yellow-brown. When fully developed, it is still red-brown, but paler than in the earlier stages, and is marked with fine, concentric, darker red-brown lines ; at the same time it loses its orange margin, and the lower surface becomes red-brown (Plate II., Fig. 2). When old and dry it is pale yellow-brown or wood colour, with concentric darker lines. The upper surface is not quite smooth, but bears numerous concentric grooves parallel to the outer edge. Fine radiating striae run at right angles to these grooves, and give the surface a silky appearance. The lower surface is studded with minute holes, or pores, which are the openings of the tubes in which the spores are produced : these holes are very small, and scarcely visible without a lens. The substance of the fructification is somewhat woody,- but it can easily be broken. The internal tissue consists of two layers, which differ from one another in colour and structure (Plate II., Fig. 3). The upper layer is white and fibrous, the fibres running more or less parallel to the surface, but the lower layer is red-brown, and consists of tubes, closely packed side by side, and perpendicular to the lower surface. In old specimens there may be two or more layers of these tubes. When the fructification dries, the outer edge curls downwards and backwards over the lower surface. When the fimgus is allowed to luxuriate unchecked, these brackets grow one above the other for a distance of two or three feet, united behind by a continuous orange - yellow cushion. At the same time fresh plates are produced at the sides of the old ones, and these fuse with the latter and make the edge of the brackets more irregular. Such masses of brackets may extend along fallen logs, or along the lateral roots of jungle stumps for several yards (Plate I.). When growing on the under surface of a log, and some- times also in other situations, the fructification of Fomes lignosus may take the form of an orange or red -brown plate, spreading flat over the surface and closely adherent to it, instead of the usual bracket shape. This is known as a resupinate or Poria form (Fig. 2). There is a very common fungus which is frequently mistaken ior Fomes lignosm, and, indeed, in the, dry state CHAP. 32 THE RUBBER TREE it is scarcely distinguishable from it. When dry it is pale Fio. 2. — Fames lignosua ; young mycelium and resupinate fructifications, xf. yellow-brown, with narrow red-brown concentric zones. It ROOT DISEASES 33 is usually smaller than Forms Ugnosus, and, deeply grooved, both radially and, concentrically. Like Fomes lignosus it curls up as it dries. When fresh, however, it is fairly easily distinguished. It is never so red-brown, and it does not have an orange margin. The lower surface is usually a dingy, livid grey, though it sometimes becomes red-brown. The best way of identifying it is to break it in two ; it is then seen to be uniformly white internally, both in the fibrous layer and the tubes, whereas Fomes lignosus, as already stated, shows two colours in section. This species is Poly- porus zonalis, Berk.. It is common on dead wood, especially on palms and bamboos, but is merely saprophytic. It has the same power as Fomes lignosus of spreading through the soil and producing its fructification on anything it happens to meet. I have seen it in abundance on living roots of Rubber as well as on bricks in a rubbish heap : in both cases the mycelium had spread from buried decaying wood. As a rule Fomes lignosus niakes its appearance in a new clearing when the trees are one to three years old. This is a consequence of the manner in which the disease originates. In the majority of cases, the fungus first develops upon a neighbouring stump. The spores of the fungus blown by the wind' alight on the dead stump, and there give rise to a mycelium which permeates the dead wood and brings about its decay. After some time, when the dead wood has been more or less destroyed by the fungus, the mycelium spreads along the lateral roots, or through the soil, and if it comes in contact with a Hevea root, it grows round and along it, giving off fine threads which penetrate into the wood and ultimately destroy it. Thus, the time when the disease is first evident on the Rubber depends to a great extent upon the time taken by the fungus to destroy the jungle stumps, or perhaps more correctly, on the time taken by it to accumulate to such a degree that it is able to spread further afield. It may also be dependent upon the time taken by the Rubber to develop lateral roots, since the fungus will then have a shorter distance to travel to reach them. It is not, however, necessary that the lateral roots of the Rubber should come in contact with the diseased roots of the stump, because the mycelium of Fomes lignosus can travel independently through the soil. 34 THE RUBBER TREE chap. It is the fact last mentioned which makes this disease so formidable, and makes its eradication so difficult. The majority of fungi only advance within dead wood, but the strands of Fames Ugnosus can travel for a few feet at least through the soil, unattached to any root or dead wood, except, of course, at their starting-point. It is always attached to its base, i.e. the stump on which it ori.ginated^| and it must derive its food from that source until it meets with other dead wood, or a living plant which it can attack. In all probability it will die if separated from its base, unless it soon meets with fresh material from which it can derive nourishment. Clear instances of the spread of the mycelium through the soil are not uncommonly met with on estates. In badly-infested areas its presence is often manifested by the appearance of the fructifications on banks by roadsides, or the sides of drains, where no roots or timber is to be seen. In some of these cases the mycelium follows smaU Rubber roots almost to the surface of the soil, but in others there is no root or wood to be found immediately behind the fructification. In other cases it is often found running on the under surface of large stones, and in these instances it is readily seen, as a rule, that it is not following a root. The best examples of this are usually to be observed on hill- sides which have been terraced with stones. The mycehums then runs more or less parallel to the -surface of the soil,| and consequently meets the wall, where it covers the stones with its characteristic strands and often produces fructifica- tions on the outer side. It may be noted that this is not an objection against terracing, since the wall to some degree stops the spread of the mycelium. Had the hill-side not been terraced, the mycelium would have spread down the slope. Free mycelium is usually found in the uppermost foot or eighteen inches of the soil, but the mycelium which runs along a root will follow the latter to greater depths. On laterals which are exposed on the surface of the soil, the mycelium travels along the lower side. The disease appears to spread downhill more rapidly than up; and when it occurs in ravines it generally spreads in the direction of the flow of the stream. As already pointed out, this disease, in the majority of ROOT DISEASES 35 cases, is due to the presence of decaying stumps. In young plantations these are, of course, the jungle stumps which were left when the land was cleared. When Fomes lignosus was first found in Ceylon, it was most frequently associated with stumps of either Jak {Artocarpus integrifolia) or the various species of Ficus. Hence it was presumed that it would be unnecessary to remove all stumps in order to avoid the occurrence of this disease, but that it would be sufficient to adopt a selective method of stumping and to get rid of the stumps of these trees which were known to serve as hosts for the fungus. In Malaya the conditions proved to be quite different. Gallagher recorded the finding of the fructification in that country on a Serdang stump, i.e. a palm {lAvistonia cochin - chinensis), and stated that the disease had been known to spread from stumps of Meranti {Shorea sp.) and Merbau {Afzelia palembanica). Bancroft added that he had frequently found the fructification on the stumps of another palm, the Mbong {Oncosperma filamentosa), as well as on stumps of bamboos and of the Kumpus {Koom- passia malaccensis) ; he concluded that the fungus occurred indiscriminately on all kinds of stumps. Further investigations in Ceylon support the con- clusions reached in Malaya. The disease has been found to originate from stumps of Tea, Cacao, Bombax {Bomhax malabaricwm), and the Bois Immortelle or thorny Dadap {Erythrina umbrosa), while the fructification has occurred on dead stumps of the giant bamboo (Dendrocalamus giganteus). The fungus has now been recorded in that country as the cause of root disease of Tea, Halmilla {Berrya ammonilla), Derris dalbergioides, Ceara Rubber, and the Coconut palm ; and in Malaya it has killed Cassava, Camphor, Liberian Cofiee, and Goffea robusta. The records cover such a wide range of flowering plants that any selective method of stumping is impossible. To avoid the attacks of Fomes lignosus all stumps must be removed. In Ceylon the eradication of jungle stumps on Eubber estates has now been fairly generally carried out. It is not, however, to be expected that, where the stumps have been allowed to remain for several years, their removal will immediately put an end to all further loss from this disease. In many instances the old, known Fomes patches have not 36 THE RUBBER TREE «=^ been thoroughly treated and continue to give trouble, wMle new cases may be expected to occur during the next two years as the result of infections which had not produced any visible effect at the time the stumps were taken out. But the principal outbreaks of this disease in Ceylon in recent years have not been due to jungle stumps, but to the following sources. As is well known, the majority of Rubber estates were originally much too closely planted, and it became necessary to thin out. In general, estates followed the course which had been advised, and uprooted the condemned trees, or at least extracted the tap root to a depth of two feet or so. In some cases, however, the trees were cut down at ground level, and the stumps left to rot, with the consequence that not only Fomes lignosus, but other root disease fungi also developed on these stumps, and they accordingly became centres of disease. Similar results followed on mixed Rubber and Cacao estates where the Cacao was simply cut down when it had to be removed. In general, the root disease which develops from Cacao stumps is Brown Root disease, but in several instances Fomes lignosus occurred. One unexpected result was the occurrence of attacks of Fomes lignosus after the abandonment or incomplete removal of Tea. It had been recommended that abandoned Tea should be uprooted in order to minimise the possibihty of attacks of tlstuUna zonata, or Botryodiplodia Theobromm, both of which were known to attack Tea, but as Fomes lignosus had never been noted as the cause of root disease in Tea, the latter was not anticipated. It has, however, since been found that Fomes lignosus can attack Tea, and several instances have been recorded in which this fungus: has developed on abandoned Tea, and spread to the inter- planted Rubber. The worst case, however, was one in which the Tea had been cleared by merely cutting it off at ground level and leaving all the roots to decay. The majority of the stumps were affected, and, as Tea bushes are planted only • four feet apart, the ground became thoroughly permeated with the mycelium of the fungus, an area of about a hundred acres being involved. The fructifications of the fungus appeared everjrnrhere, on Tea stumps, dead wood, roadside n ROOT DISEASES 37 banks, and drain sides. A trench was dug round the whole area, but trenching round individual infected patches was impossible, and, instead, trenches were dug round groups of apparently healthy trees. Dead trees, or trees which had lost their tap roots, were removed and burnt, and the roots of all trees examined, and treated when necessary, while the ground was limed with a general dressing of 2000 pounds of lime per acre, in addition to 60 pounds for each dead tree. A fair proportion of the trees were saved by these methods. Another unexpected development of Forties lignosus over a large area followed the operations attending the removal of large examples of the thorny Dadap {Eryihrina umhrosa). -The estate had been originally in Cacao, through which the dadaps had been planted as shade trees. Subsequently it was interplanted with Hevea, and when the latter grew up it was decided to take out the dadaps, which were then about thirty years old. They were accordingly ringed at a few feet from the ground and left to die. In about five years' time the trees began to fall, and shortly afterwards Fomes lignosus was found to have developed in abundance not only on the stumps, but also along the fallen trunks. It will be evident from the examples given that from the point of view of root disease it is unsafe to leave stumps of any kind among rubber. The symptoms exhibited by trees attacked by Fomes lignosus difier, apparently, according to the part attacked. Sometimes the laterals are first attacked, sometimes the tap root, but which of these happens is purely a matter of chance. When the tap root only is attacked it is frequently completely decayed before the trees show any symptoms of disease. In one of the earliest cases recorded in Ceylon nothing was observed to be wrong with the trees until seven hundred, on an area of about eighty acres, blew over in one night. It was then seen that in every case the tap root was decayed, and the trees had been supported only by the laterals. When the tree is not blown over the fungus gradually ascends to the collar and attacks the laterals near their base, and, in consequence, the tree dies more or less suddenly. Trees which have lost their tap roots can some- times \m recognised by the shape of the lower part of the 38 THE RUBBER TREE chap. stem, which often becomes fluted. When the tap root has been destroyed, the increase in girth is apparently greatest over the main lateral roots, so that a vertical ridge is developed on the stem above each of them. This appearance often proves useful in the detection of diseased trees round one which has already succumbed. When the attack begins on the laterals the smaller branches may die back generally, i.e. all over the crown, and the tree become stag-headed some months before it dies. This is another appearance by which diseased trees niay be detected round a known Fomes patch, but it is not universally a sign of root disease. Sometimes the leaves turn yellow before the branches die back. In other cases an extensive fall of leaf occurs, especially in wet weather. In some cases the flow of latex ceases in an early stage of the disease, while in others it continues until the leaves turn brown and the -tree dies. If only the laterals on one side of the tree are attacked, very little may be noticeable for a long time. In the following instance the course of the disease was watched almost from the beginning. The tree, which was one whose yield per tapping was being recorded, shed part of its foliage during wet weather in August and ceased to jdeld latex. The tap root and the laterals for a distance of two or three feet were examined, but no Fomes mycelium was observed. The tree continued dry imtil the following February, when it wintered and produced new foliage. It then yielded latex for a few weeks, but soon went dry again, and the new foliage at the tips of the branches began to turn yellow. When the roots were examined again in May, Fomes mycelium was found on the laterals advancing to within a short distance of the stem. Thus the effect of the disease had been manifested by the fall of the leaves and the cessa- tion of the latex flow, about nine months before the mycelium had travelled along the laterals far enough to be discoverable by the methods usually employed. In contrast to the foregoing, a tree in the neighbourhood of an old-estabhshed Fomes patch has been found to have all its laterals covered with a network of mycelium, without showing any die-back in the crown, or falling off in the yield of latex. ROOT DISEASES 39 It is scarcely possible to give any definite estimate of tlie time wMcli elapses between the beginning of an attack and tlie death of the tree, as so many different factors may in- fluence the course of the disease. Young trees may be expected to succumb more quickly than old trees. The growth of the mycelium is to some extent dependent on climatic conditions, and it is not necessarily most rapid in swampy land. The effect will differ also, as already pointed out, according to whether the laterals or the tap root is first attacked. Observations in Ceylon would appear to show that the presence of the disease is manifested earliest when the laterals are attacked first. Taking all circumstances into consideration, it is probable that the majority of the trees attacked die within twelve months. Though infection from a dead stump is the most usual way in which Fomes lignosus attacks Hevea, it is to be expected that, as the fimgus is parasitic on Hevea, cases will occur in older Rubber through direct infection by means of spores, more especially on exposed or injured lateral roots. One case, at least, which could not be explained on any other supposition, has been noted in Ceylon. The tree was twelve years old, and was growing in Tea twenty-five years old. All jungle stumps had long since disappeared, and there was no root disease on the surrounding Tea. Such cases are, however, rare. Infection by spores has been considered improbable, because, when the fructifications have been examined, they have been found to bear very few spores, or in some cases none at all. This is probably merely a matter of examining the fructifications at the right stage. There can be no doubt that under " wild " conditions the dissemination of the fungus to different centres is effected by spores, and, indeed, its occurrence on Cacao stumps on old Cacao estates, on Rubber stumps after thinning out on previously clean areas, and on abandoned Tea some twenty years old is clear evidence of spore infection. Many other similar cases are available. It occurred, for example, on the roots of the famous row of Ficus ektstica at the entrance qf the Peradeniya Gardens, when these were felled at the age of about eighty years, though the surrounding area had been cleared for the same period ; and it similarly developed at Peradeniya 40 THE RUBBER TREE chap. on the stumps of Giant Bamboos (Dendrocahmus giganteus) which died after flowering at the age of about fifty years. Moreover its occurrence on jungle stumps in new clearings can only be explained by spore infection, for it is quite contrary to all experience in field mycology to suppose that all such stumps were attacked by Forms Ugnosus before the jungle was felled. In Malaya this disease is said to be worst on clayey soils or on peaty land. On the latter it is frequently very difficult to eradicate, owing to the presence of buried logs. Thorough drainage is of the greatest importance in both cases. The treatment of Fomes Ugnosus follows the usual lines of digging out and burning diseased roots and all dead stumps or rotting timber, liming the patch, and surrounding it by a trench (see p. 24). It is very important that the diseased laterals should be followed up as far as possible and lime scattered especially along their path. Lack of success in treating Fomes is frequently due to neglect of this point. Another cause of failure is the unwillingness of the planter to put the trench far enough away from the original dead tree. By the time one tree has-^died the lateral roots of the surrounding trees have in many cases been attacked, and if these have not been isolated the disease will in all probability have travelled a row farther on before they in turn die. The trench should always be cut so as to include the four nearest trees, even if the latter appear quite healthy. Many estates practise double trenching, especially where more than one tree has died. The first trench encloses the dead trees and those immediately round them, while the second is dug a row outside the first. The ground should be forked over, and all dead wood and diseased roots removed as far as possible before the trenches are dug ; otherwise they are buried beneath the excavated soil. It is not un- common to find roots about the thickness of a pencil covered with mycelium, and often producing fructifications, in treated Fomes patches. It is often possible to pick out diseased trees round a Fomes patch by a fluting at the base of the stem, or a general die-back of small branches all over the crown. The roots of such trees should be opened up and examined, and if they are badly attacked, or if the tap root is decayed, they should ROOT DISEASES 41 be removed immediately. The lateral roots can be laid bare for a distance of about three feet from the stem, and the tap root to a depth of two feet, without endangering the stability of the tree. All trees enclosed within the trench should be examined in this way. If only one or two laterals are decayed, these may be cut back into sound tissue and the wound tarred. In some cases, where the disease has only just attacked the roots, it has been possible to treat them by scraping ofE the superficial myceHum and painting them with Brunolinum or other preservatives, or even with tar. This possibility depends on the fact that the superficial mycelium frequently spreads for some distance along a root before penetrating it. But if the bark and wood beneath the mycelium is attacked, either the diseased part or the whole root must be cut out. It is necessary to inspect Fomes trenches periodically to see whether the fructifications are developing on the sides. These should be removed and any dead wood from which they are growing dug out. If they develop on the outer wall of the trench, it is a sign that the trench has not been made far enough away, and it must be extended by a loop on that side which should include at least the next tree. Brown Root Disease ' {Fomes lamaoensis, Murr.) This disease appears to be the most widely-spread root disease of cultivated plants in the Eastern Tropics. It was apparently originally found on Bread-fruit trees in Samoa, where it was said to cause very serious damage. The next report of it was on Tea in Northern India : in this case the principal features of the disease were described by Cunningham, and though he did not discover what the fungus was, it is clear from his description that he was dealing with this disease. Similarly, Zimmermann found it attacking CofEee in Java, but was unable to ascertain the identity of the fungus which caused it. It was first recorded on Hevea in Ceylon, and it is probably the commonest root disease of the Rubber tree in that country. Yet, except under special conditions, it does not cause so much damage as Fomes lignosus. The latter can spread 42 THE RUBBER TREE CHAP. independently through the soil from a jungle stump, and may attack a number of trees in one spot before any of them is so seriously affected as to show signs that there is something amiss. Brown Root disease, on the contrary, spreads very slowly, and, for all practical pur- poses, only along the roots of the tree ; consequently it only infects the neighbouring trees when their roots are in contact with those of the diseased tree, and the progress of the fungus is so slow that, as a rule, the first affected tree is dead before the neighbouring trees are attacked. In general, therefore, only one tree is killed at • each centre of infection, unless the dead tree is left standing for a long period. When the dead tree is dug up, the special characters of Brown Root disease are usually immediately evi- dent, and, as a rule, there can be no mistake in the diagnosis. The roots (Fig. 3) are encrusted with a mass of sand, earth, and small stones to a thickness of three or four millimetres ; this mass is fastened to the root by the mycelium of the fungus, and, consequently, cannot be washed off. The mycelium consists of tawny brown threads, which are collected here and there into small sheets or loose masses, either on the surface, or embedded in the crust of soil and stones. The colour of the myce- lium varies, and one frequently finds brownish-white, or almost white, masses intermingled with the tawny brown. In the early stages the predominating coloiir of the mycelium is brown, and this is usually the case when the Fio. 3. — Fomea lamaoenaia ; mycelium on root, x J. ROOT DISEASES 43 roots of a dead tree are examined. Hence the name Brown Root disease. But when the disease has been established for a long time, and the fungus has grown older, it forms a black, brittle, continuous covering over the brown masses of hyphae, and the diseased root then appears chiefly black. The brown mycelium is, however, immediately discernible if the black crust is cut. In all stages the encrusting mass of earth and stones, intermingled with brown threads, serves to distinguish this disease. The root looks as though it had been dipped in glue and then had soil and stones scattered over it. Bancroft stated that the surface of the root becomes dark brown and almost black, and for that reason the coolies in Malaya know the disease as " Sakit hitam." In the case of young trees the encrusting mass is usually most strongly developed on the tap root, and it may ascend up the stem for several inches. On old trees, however, the appearance may be different, especially if the tap root is the part first attacked. In that case, owing to the slow effect of the disease, the tap root may be in an advanced stage of decay, before the fungus has spread to the laterals sufiiciently to cause any marked symptoms in the crown. The cortex with its covering of earth and stones may by that time have dis- appeared completely from the tap root, owing either to decay or to the attacks of white ants, and it is then necessary to examine the laterals to find the characteristic external appearance of the disease. But even when the outer crust has disappeared the disease may usually be identified by the appearance of the wood. In some cases, after the tap root has been attacked, the tree produces new roots at the collar, and these grow down vertically and take the place of the missing tap root. As Bancroft has pointed out, this is an indication of the slow progress of the disease. I have, however, seen the same thing in a case of Fomes lignosus, where the disease had for some unknown reason been arrested after the tap root had been destroyed. If the encrusting mass is cut away, the cortex on the diseased roots is found to be brown, or brown mottled with small white patches internally. The diseased wood usually shows characteristic markings, though these may be of two 44 THE RUBBER TREE chap. entirely difEerent types. In the one case the wood is soft and friable, with a network of fine brown lines (Plate II., Fig. 7), and even with a hand lens it can be seen that these lines are composed of brown hyphae. Thin sheets of brown hyphae run through the decaying wood, and these appear as brown lines when the wood is cut. This is the more frequent appearance in the lateral roots. In the other case the wood of the root is comparatively hard, and traversed by rather broad brown bands (Plate II., Pig. 8), in which no hyphae are discernible. This may occur in the lateral roots, but is more usual at the base of the stem. There is some evidence that the appear- ance first described follows the second. In either case the wood in an advanced stage of decay may be honeycombed, the brown^plate^ persisting after the tissue between them has almost completely decayed. A few narrow black hnes are usually present in the diseased roots, but the brown lines are more mimerous. In advanced cases, black circles are sometimes found when the cortex is stripped off a diseased root. Brown Root disease, in its most general form, might be regarded as a " dry rot," but I have seen advanced cases where the honeycomb structure was well developed, in which the cells of the honeycomb were filled with water. This disease often appears on old trees as a " collar rot," i.e. an area of rotten, decayed bark, more or less triangular in outline, and broadest below, extends upwards from ground level on one side of the stem for a height of a foot or so. The wood behind this region is decayed and rotten, and may weather away, leaving a large cavity at the base of the tree. This effect is produced by an attack of the fungus on a lateral root, and its advance along the lateral to the base of the stem, which is attacked round the point of origin of the lateral. This mode of attack is very common in cases where the fungus first develops on Cacao stumps and spreads from them to the Hevea ; and in such cases it is easy to pick out the affected trees by the rotten patch of bark at the base, before any effect is observable in the crown. UstuUna zonata frequently works in the same way. When the fungus has first attacked the tap root, it often advances up the centre of the stem and causes a " heart rot," i.e. it affects the central heartwood more rapidly than the ROOT DISEASES 45 outer younger sapwood. A more or less conical decayed region extends up the centre of the stem, sometimes for a length, of a couple of feet, the boundary being discoloured and evidently diseased, but still solid, while the inner parts are converted into a honeycomb structure with brown walls, with white fragments of the decayed wood in the cells. If such a stem is cut across above the evidently diseased part, a white covering of myceUum usually appears in the centre of the section within a few days. A curious variant of the foregoing was recorded in one case. The tree had apparently had what is Imown as a " heart shake," i.e. the wood had split near the centre of the tree along the line of an annual ring. When the fungus grew up the stem it filled the crack with a thick felt of brown mycelium to a height of about three feet. As indicated above, this disease is not confined to Hevea, but attacks cultivated plants of all kinds, except (as far as is known at present) the short-lived annuals. In Ceylon i^ has been recorded on Ceara Rubber, Castilloa elastica, Cacao, Tea, Dadap {Erythrina), Caravonica Cotton, Camphor, Cinna- momum Cassia, Erythroxylon Coca, Brunfelsia americana, Thespesia populnea, Hura crepitans, Grevillea robusta, Codi- aeum variegatum (Croton), Brownea grandiceps, Jak {Arto- carpus integrifolia). In the Federated Malay States it has been found to attack Hevea and Camphor ; Brooks and Sharpies state that it is infrequent on the former, and usually attacks trees under two years of age, though Bancroft recorded that it appeared to be fairly common on certain areas. It has been recorded from Samoa on Hevea, Castilloa, Cacao, Bread- fruit and Albizzia stipulata, and from Java, on Hevea and Coffee. In Southern India it is known to occur on Tea and Hevea, and in Northern India on Tea and various shade trees. In West Africa it attacks Hevea, Cacao, and Fun- tumia. On new clearings the fungus spreads to the Rubber from decaying jungle stumps and rotting timber, and this may go on as long as either of these remain. In one case (on Tea) the fungus was found to spread to the Tea from decaying stumps of Na (Mesua ferrea), the Ceylon Iron-wood, which were at least fourteen years old. But by far the greater 46 THE RUBBER TREE chap. number of cases which occur in Ceylon are on old Cacao land, after the Cacao has been felled. Brown Root disease is the only root disease of Cacao known in Ceylon. Comparatively few Cacao trees are killed by it, but the fungus develops freely on the Cacao stumps whenever the Cacao is cut down. In 1905 this occurred on several estates on which alternate lines of Cacao had been cut out to make room for Rubber, and in some cases it proved difficult to eradicate, owing to the large number of Cacao stumps, each of which was a potential centre of disease. When writing on this disease in 1911, it was pointed out that where Hevea and Cacao had been interplanted it would ultimately become necessary to remove the Cacao ; and when that step had been decided upon the Cacao shotdd be up- rooted, not merely cut down, if attacks of Brown Root disease were to be avoided. Recent events have amply justified that statement. On several estates where the Cacao has Ijeen removed during the last five years, by merely felling the trees and leaving tihe stumps, Brown Root disease has been rampant, upwards of ten per cent of the trees having been attacked. In such cases the cost of treating the disease has been much greater than the cost of removing the Cacao stumps originally would have been. Another instance of the association of Brown Root disease with the stumps of cultivated trees recently came to light in Ceylon. On one group of estates, the boundaries and roads were planted up with the white cotton, or Kapok, tree, Eriodendron anfractuosum. Naturally, with such a large and rapidly-growing tree, it soon became evident that they had to be taken out, and when that was done they were simply felled, and the stumps allowed to remain. In the course of a year or two, numbers of these stumps became centres of Brown Root disease, which spread to and kiUed the adjacent Rubber. Brown Root disease has also been found to spread to Rubber from a felled Hevea log which had been accidentally buried during the construction of a road. In the most general case Brown Root disease spreads from one tree to another, or from a dead stump to a neigh- bouring tree, only when the roots of the two are in contact. Instances of this may be quite commonly seen where the ROOT DISEASES 47 disease has originated on Cacao stumps. But it may be worth while putting on record two cases which give some evidence that it might be possible for the mycelium to spread through the soil, at least for a short distance. In one case a Rubber stump attacked by this disease was planted in a flower pot at the laboratory, and, in course of time, the mycelium extended from the stump to the wall of the pot on one side, binding together the particles of soil in a mass about two inches thick. _ But it did not pass through the wall of the pot, as the mycelium of Poria hypohrunnea will do under similar conditions. In the other case the mycelium spread along dead leaves, etc., at the collar of a diseased Brownea grandiceps for a distance of about four inches all round. "When this case was found, the mycelium had lost its hyphal character and had formed, on the under side of the dead leaves, a black film covered with a brown powdery layer. This powdery layer can frequently be observed overlying the black crust on diseased roots ; it consists of a number of minute spore-like bodies, which, however, do not appear to be true spores. Though, as already stated, this disease is often associated with decaying stumps and timber, there are very many cases, in Rubber, or Tea, or on ornamental trees in Botanic Gardens, in which no stump or decaying timber can be found anywhere in the immediate neighbourhood. In such cases it is obvious that infection must take place by means of spores conveyed to the plant by wind or other agency. But here we were until quite recently faced with the difficulty that no one had been able to find the spores of the fungus, or, indeed, had met with the fructification of the fungus in other than a rudiment- ary condition. As a rule, a dead tree is found and dug up before the fructification has developed, and the treatment which will cause the production of the fructification of, say, Fomes lignosus in the laboratory from diseased roots is usually unsuccessful in the case of Brown Root disease. Even when dead trees have been left standing for some years, until they have finally disappeared owing to the attacks of white ants, no fructification has been formed. On yoimg Rubber, or other small trees which have been killed by this disease, the fungus sometimes ascends the stem externally above the collar, and there forms a tawny or dark brown crust, free of earth and stones. In Ceylon these 48 THE RUBBER TREE chap. patches are usually small, not more than an incii or two in diameter, but in some countries they are said to cover the stem all round for a length of several inches. Bancroft stated that the only fructification he obtained in Malaya was a badly-developed specimen on Camphor, but that he had seen specimens on Cacao from West Africa in which the brown crust ringed the stem at the collar for a distance of about three inches. These brown patches are minutely velvety, being covered with very small projecting bristles or setae. Such structures are characteristic of the genus Hymenqchaete, the species of which form, as a rule, flat, encrusting, brown plates, velvety with the bristles in qiiestion. Hence it has been customary to consider that the fungus of Brown Root disease is a Hymenochaete, and to adopt for it the name Hymenochaete noxia, which is that given by Berkeley to the fungus on Bread-fruit in Samoa. But during the last few years, more particularly during 1917, perfect fructifications have been found in Ceylon on several occasions, on jungle stumps, on Tea and Hevea killed by Brown Root disease, and on rotting Hevea logs. These show that the fungus is really a Fames, and that the brown patches hitherto observed, the supposed Hymenochaete, are merely abortive attempts to produce the Forms sporophore. This Fomes is figured on Plate II., Fig. 10. It is bracket- shaped, often irregular and consisting of several brackets fused together. The separate brackets are three or four inches broad, and about one-third of an inch thick, and very hard. The upper surface is purple-brown, usually concentric- ally grooved, and glabrous. The lower surface is dark brown, or almost black when moist. When broken in two it is seen to consist of a hard, dark, outer crust, with lighter brown tissue internally. The specimen figured (Plate II., Fig. 9) is a lighter brown than usual. The internal tissue usually shows a concentric zoning, with curved transverse lines parallel to the margin. The pores or tubes on the under surface are lined with setae, similar to those which occur on the supposed Hymenochaete patches. The fructification is peculiar in that its internal tissues are built up of two kinds of hyphae, the one thin-walled, like fungus hyphae in general, the other thick-walled and resembling the setae in structure. The name of this species is Fomes hmaoensis. It frequently ^J!^— ■ ROOT DISEASES n ROOT DISEASES 49 occurs in resupinate form, i.e. lying flat on the root or stem. The discovery of the Fomes fructification clears up the difficulty of accounting for the distribution of the disease. It is now evident that infection can be conveyed by wind- borne spores from the fructifications on decaying stumps or timber in the jungle or elsewhere. But in Ceylon the fructifi- cation is by no means common, and it would seem that special cHmatic conditions are required for its development. In illustration of the rate at which the disease spreads the following instance may be cited. Hevea was planted, 14 feet apart, in a single line round the boundary of an old- established Cacao estate. When the trees were eight years old one of them died, from Brown Root disease as was subsequently discovered. The tree was left standing and allowed to decay. Two years later the next tree in the line died and was likewise left to decay. After a further period of two years had elapsed, the next tree in the same direction along the line failed to recover after wintering and was evidently dying ; and an examioation of this tree and the two old decaying stumps proved that they had all been killed by Brown Root disease. Some of the neighbouring Cacao was also killed during the four years, but the path of the fungus from one Hevea to the next had been along the rubber roote. Anstead has recorded an experiment in which a diseased root was buried in contact with the roots of a healthy tree, with the result that the latter was infected and died. Dead trees should be dug up, with as much of the roots as possible, and burnt. Any neighbouring stump should be sinularly treated. The affected spot should be dug over, aU dead wood collected and burnt, and lime forked in. In general, practically aU the fungus is removed with the dead tree, and in many cases trenching has been dispensed with. But owing to the -uncertainty of removing all lateral roots, it is better to err on the safe side, and to trench round the affected area. When extensive attacks of Brown Root disease occur on old Cacao land, the decaying Cacao stumps must be dug up and burnt. This will generally entail forking over the whole area. It should then receive a dressing of lime at the rate of 50 THE RUBBER TREE chap. at least a ton an acre, in addition to the application of the usual quantity, sixty pounds, to the site of each dead tree. In such cases it is usually possible to detect many trees in an early stage of the disease by noting the occurrence of patches of decayed bark at the collar where a diseased lateral joins the tap root. These cases should be treated by removing the decayed lateral root and all diseased wood and bark at the base of the stem. The cavity should then be tarred, and it would be advisable to fill it up with cement or concrete. The experiment of immediately replanting a tree of the same species in the place where one had just been killed by this disease was tried at Peradeniya several years ago, and the " supply " has remained healthy. It would therefore appear probable that vacancies might be filled as soon as all dead wood has been removed and the ground limed. But it would perhaps be safer to wait for about six months. Wet Rot (Fomes pseudo-ferreus, Wakefield) This root disease has been recorded only from Malaya. It was at first attributed to Poria hypolateritia, a common root- disease fungus of Tea in Ceylon, but further fructifications of the fungus have since been obtained, and these have been found to be an undescribed species, which has been named Fomes pseudo-ferreus by Miss Wakefield. The chief characteristic of the, disease is the wet rot of the roots attacked. This may vary from a sKght dampness only detected on splitting the root, in the case of roots recently attacked, to the complete disorganisation of the tissues into a jelly-like mass. The external appearance of the diseased roots does not ofier any good diagnostic characters. The roots are some- times slightly encrusted with sand, but not to such an extent as in Brown Root disease, and the crust lacks the small masses of brown mycelium which characterise the latter disease. They resemble to some extent old cases of Poria hypobrunnea, and this resemblance is increased by the occur- rence in some instances of a dark red superficial mycehuiii. The exterior of a diseased root is sometimes covered with a very dark reddish skin, which is .tough and can readily be ROOT DISEASES 51 detached from the wood when the root is first dug up. The skin consists of mycelium and bark tissues intermingled. Sometimes a very delicate snow-white mycelium is produced in patches on the exterior of the smaller roots, but no free strands have been observed travelUng through the soil. The action of the fungus on the cortex is peculiar. The middle layers of the cortex appear to be especially attacked and disintegrated, with the result that the outer layers of the cortex disappear, or can be easily removed, leaving the decayed root enveloped by a very thin, white, papery layer, which consists of the inner layers of the cortex only. This is especially noticeable on roots two or three inches in diameter. The diseased wood may be permeated by brown lines, or plates, of fungus tissue, or broad bands of some substance akin to wound gum, and it may be honeycombed ; but these features are commoner when hardwood jungle stumps are attacked than in the case of Hevea. In many cases the wood does not show any coloured bands or plates at any ^tage of decay. In advanced stages of decay the wood may become a spongy mass in which its origiual fibrous character is entirely lost. Pieces of root which have undergone this change may be enclosed in the thin white layer noted above, which forms a continuous outer coat readily distinguished from a wood surface by the presence of the transverse scars of the lenticels of the root and the scars of the smaller rootlets. The fungus has been found on both hard- and soft-wood stumps, including many of the largest stumps which are often left on estates where the smaller stmnps have been removed. Perfectly-developed fructifications of the fungus are rare, and the present description of it may require modification when further specimens are available. Imperfect fructifica- tions occur as small patches on the under surface of exposed roots. In the most fully developed form hitherto observed the fungus forms a small bracket, hoof-shaped or flattened, white at &cst, becoming dark brown with a white margin. The upper surface is smooth and hard, and cracks in drying. In section the upper part is woolly, and varies in colour from cinnamon to brown, and the lower part, which consists of the usual Fomes layer of parallel tubes, is of the same colour. The lower surface is whitish, and becomes yellow when bruised. 52 THE RUBBER TREE chap. The disease has been found throughout Malaya, but it has not yet been recorded from other countries. Up to the present no spores have been found in the fructifications seen. Infection of the Rubber trees takes place by contact of the lateral roots with the diseased roots of jungle stumps, or of Rubber trees already attacked. The disease progresses very slowly in living tissue, and it is possible for many trees to be infected, through their laterals, before the first infected tree is seen to be diseased. The fungus seldom rings a tree, but goes up to the collar on one side only. It is said to prefer heartwood to sapwood, and to travel up the centre of a root, leaving the outer tissues untouched. It has been recorded that, on an estate in Malaya, thirty per cent of the trees in one field were affected before the presence of the disease was suspected. The disease is usually discovered earlier on wet lands, as the roots are poorly developed in such situations, and the trees blow over sooner when attacked. According to Belgrave, trees are rarely killed by this disease before their eighth year, and the average time for the discovery of the disease on plantations is ten to twelve years. Trees which have been planted very close to jungle stumps may be killed in five years. Until further details of this disease are known, treatment should follow the usual lines for root diseases in general. Red Root Disease {Poria Tiypohrunnea, Fetch) This disease was first seen in Ceylon in 1905. Only one tree, about two years old, was attacked, and as no further cases were observed for many years it was considered probable that the fungus found in that particular instance was merely ' saprophytic. In 1914 it occurred rather commonly on Hevea and Tephrosia Candida in a new clearing on the Experiment Station at Peradeniya, and since then it has been recorded from several estates in the low country. Up to the present it is by no means a common root disease of Hevea in Ceylon, and ranks, in point of frequency, rather with Sphaerostilk^ repens than with any of the other root diseases. It has also*' n ROOT DISEASES 53 been recorded from Java, but the Hevea root disease assigned to Poria in the Federated Malay States is now known to be different. The appearance of the diseased roots is very variable, and, in consequence, its diagnosis is in many cases somewhat difficult. On young trees, up to about two years old, its identification is fairly easy. The tap root then usually bears external myceUum in a more or less young stage, and in that condition it is unmistakable. The mycelium forms stout red strands on the exterior of the root, which sometimes unite into a continuous red sheet (Plate V., Fig. 4). The strands are smooth and tough on the outside, not woolly, and vary in colour from a bright red to brownish-red, according to age. Internally they are white, so that, if they have been damaged in digging up the root, they appear red and white. When old the strands turn black, and one might pass over the case as one of Ustulina in which the fungus had abnormally produced external mycelium. Again, some stones may adhere to the strands, and give the impression that one has to deal with a case of Brown Root disease. But the root is never so encrusted as in Brown Root disease, and there is no brown mycelium between the stones, while it lacks the fans between the wood and the bark which are characteristic of Ustulina. In most cases on young trees it is possible to find the red mycelium : if it has turned black on the lower part of the root some red pieces can usually be found at the collar. The appearance of the diseased wood is also typical in the case of yoimg trees (Plate V., Fig. 3). It is somewhat soft and friable, and is permeated with red sheets. , These sheets often run in cylinders in the wood, along the lines of the annual rings, so that they divide the wood into layers, which separate easily from one another and have a red surface. On older trees the indications are by no means so clear. All the mycelium may then be black, though it is often possible in such cases to find red patches or strands on a lateral which has been more recently attacked. Exposed wood surfaces are usually coloured red-brown. The roots which have been longest diseased are generally soft and wet, and on these there may be a network of narrow white threads between the bark and the wood. The coloured sheets in the wood turn brown when old, or may even become black. I have, how- 54 THE RUBBER TREE chap. ever, seen the typical red sheets in a twenty-year-old Hevea where a diseased lateral joined the stem. The fructification may sometimes be found at the collar of a diseased tree, or along the under side of exposed lateral roots. It belongs to the same group as Fomes, i.e. it is a Polyporoid fungus, though it does not produce a bracket, but forms a flat plate closely applied to the surface of the root or stem. At first it is yellowish-white, or ochraceous ; it then changes to reddish-brown, and finally to a dark slate colour (Plate II., Fig. 5). In section it is blackish-brown, with a reddish tinge in the intermediate stage (Plate II., Fig. 6). The upper part consists of a layer of tubes, while the lower part is somewhat loose and woolly, though it varies considerably in texture. Its thickness is usually about one and a half millimetres, and it may spread over an area of several inches. In its occurrence on the Experiment Station, Peradeniya, there is no doubt that it spread to the Rubber from the jungle stumps. Its recent appearance on Rubber estates, about twelve years old, where it was not previously known, is probably to be attributed to the way in which the thinning out was done. It has been found to develop from the stumps of felled Hevea, where the trees were cut down at ground level and the stumps left to decay, and it is one of the mOst regular frequenters of rotting Hevea logs. It is always possible to find the fructifications of Poria hypohrunnea on Hevea logs which have been left to rot, and it is highly probable that to this practice the present attacks of this disease are to be attributed, at least in Ceylon. The fungus is not unconmion on rotting logs in the jungle or elsewhere, and the spores from that source infect the Hevea logs lying about the estate. Its simultaneous occurrence on Rubber logs all over an estate is direct evidence of a distribution by means of spores. On young clearings, and in older Rubber until the stumps are removed, the fungus spreads to the Hevea from the lateral roots of the jungle stumps, whether by contact or otherwise. Where felled Hevea has been left to rot, it is most probable that it may spread from the logs to the Hevea roots by contact, while the fructifications provide spores which can distribute the disease further. It has been found n ROOT DISEASES 55 on lateral roots of Hevea two inches in diameter left in the ground after thinning out. That the mycelium of the fungus can travel from the diseased roots for some little distance, at least, through the soil was demonstrated by the following experiment. A lateral root of Hevea, aboiit three inches in diameter, attacked by Poria hypobrunnea, was planted upright in the centre of an ordinary twelve-inch flower-pot, and covered with a bell glass. In a few weeks the mycelium had travelled from the root to the side of the pot, had penetrated through the wall of the pot, and was producing a fructification on the outside. With regard to the rate at which the disease progresses, the following may be noted. Hevea was planted on newly- cleared land in June 1913 ; the trees began- to die in 1914 : that is quite as rapid as any other root disease. Further, the era of thinning out in Ceylon may be taken as 1913-1916, while the appearance of Poria as a root disease on Ceylon estates dates from 1916. Allowing a year for the develop- ment of the fungus on Hevea logs or stumps, this again indicates a progress equal to that of other root diseases. The treatment of Poria hypobrunnea follows the usual lines. But it is especially necessary that all Hevea logs should be removed, as the fungus develops chiefly on them. Poria hypobrunnea may be said to prefer logs. It was collected in Ceylon on several occasions before it was known to be the cause of a root disease, and in all cases it occurred on decaying logs, both in virgin jungle at an elevation of 5600 feet and in secondary jungle and scrub at an elevation of 1500 feet. Besides Hevea, this fungus has been found to attack Hibiscus (Shoe flower), Panax, Tephrosia Candida, Crotalaria fulva, and Tea. JJSTULTNA ZONAl'A, Lev. This fungus has been known for many years as the cause of the commonest root disease of Tea in Ceylon. It is by no means selective with regard to its host plants, having been found to attack Pumelo, Ebony, Scolopia, Cassia javanica, Derris, Halmilla {Berrya ammonilla), Lunuraidella 56 THE RUBBER TREE ohap. [Melia dubia), etc. As the cause of a root disease of Hevea, it is common in the Federated Malay States, and fairly frequent in Ceylon. It has also been found to attack Hevea in Java and Fiji. The disease usually attacks old trees, though cases have been seen on trees only two- or three years old. On the older trees it is frequently discovered as a " CoUar rot " on one side of the stem, i.e. the bark is decayed on one side from ground level to a height of one or two feet, often in a more or less triangular patch broadest at the base, and the wood behind the patch is rotten. In Ceylon such cases are usually the result of an attack via a lateral root, the fungus having travelled along the lateral to the base of the stem, but in Malaya they can arise at the collar independently of any attack on the laterals, and the fxmgus attacks the latter later. The decayed bark and wood frequently weathers out, leaving a large hole at the base of the stem on one side. This collar rot and formation of cavities at the base of the stem is not peculiar to Ustulina, but occurs also in Brown Root disease. In other cases the fimgus attacks the tap root below the region where the larger laterals arise, and works completely through it. It advances for some distance up the middle of the stem, but, in general, does not descend far down the tap root. It frequently happens that when the upper part of the tap root is quite decayed, the part a foot or so below groimd does not show any signs of the fungus. The cortex on the lower part of the root then turns bluish or purple internally, and the root has an offensive smell : specimens in this condition superficially resemble roots killed by Sphaerostilbe repens. When the tap root is destroyed the tree is often blown oyer before any sign of disease is noticeable in the crown. Similarly, when the tree is attacked on one side at the base, the disease is usually discovered before the crown has begun to suffer. But failing either of these, the fungus gradually travels round the stem and along the laterals, and as the decay of the base and the roots progresses the branches gradually die back. In Ceylon the progress of the disease on the individual tree appears to be slow. Death of the tree may not occur until a long time after a large hollow has been caused on ROOT DISEASES 57 one side. Latex is still obtainable on the sound side of the tree, and in several instances an abnormal flow of latex has been reported from trees badly attacked on one side by Ustulina. An extreme example of the slow rate of progress of this disease on some trees other than Hevea is furnished by a Eugenia in the Royal Botanic Gardens, Peradeniya. The base of the stem on one side is severely attacked, and produces successive crops of fructifications in every monsoon. But it is known to have been in this condition for at least ten years, and the only effect observable to the casual observer is the death, now and again, of one of the thinner topmost branches. It is to be noted, however, that if the course of the disease is slow it is in consequence more to be feared, as a large number of trees may be attacked before anything serious is noticed. Sharpies states : " This root disease is common on most of the older plantations in the Federated Malay States, though its presence is unsuspected . The fungus works slowly and insidi- ously, the crown of leaves becoming thin as it pro- gresses in the collar. The diseased tissue is usually confined to one side of the coUar, and from this side latex cannot be obtained. The opposite side may give a good yield, and tapping is continued till the amount of latex obtained begins to diminish. When this stage is reached the tree soon dies and is taken out." The affected wood at the base of the stem is permeated with conspicu- ous black lines (Fig. 4). These run irregularly up and down the stem, or transversely. The wood is divided FiQ. 4. — Ustulina zonata; black lines in wood. X J. THE RUBBER TREE CHAP, 58 up by thin sheets of black tissue, and the edges of these sheets appear as lines when cut. Sometimes these sheets form closed pockets, and in section appear as irregular ovals or circles surrounding dark - coloured patches of diseased wood. Between the black lines the wood is sometimes uniformly brown (Fig. 5). Emphasis is laid, in the Federated Malay States, on the fact that the diseased wood is dry and tindery, " like touchwood," and hence the disease has been named " Dry Root and Collar Rot." Typical characteristics of the disease on the roots are best seen by examining the laterals. There is no external myceliujn, such as is foimd in Fomes lignosus or Brown Root disease. The roots (Fig. 6) frequently bear small black nodules, two or three millimetres in diameter, which are white internally and may appear white on the top if they have been damaged when the root was dug up. They are usually scattered, and not in large numbers. They are formed by the emergence of the mycelium from the diseased tissues, and, had the root been exposed, would no doubt have developed into fructi- fications. In advanced cases there is frequently a continuous, thin, black layer or crust beneath the outer papery layer of the root. Between the bark and the wood there is generally a thin film of white or brownish mycelium, arranged in fans (Fig. 7), frequently with black lines bordering the outer ends of the fans. This last is the most characteristic feature of roots attacked by Ustulina, whether Rubber or Tea. As in the stem, irregular black lines are usually present in the wood of the root. It may be noted that although black lines occur abundantly Fio. 5. — Ustulina zonata ; black lines and brown areas in wood, x J. ROOT DISEASES 59 in wood attacked by UstuUna they are not invariably an ■^ • .- ■■^-^^, v^'^" ■■-■■■# \ , -y '■■■ ^'-^ ' ■,^^r ''-^ Fig. 6. — ^Root attacked by UsttUina zonata, showing external black cushions, x J. indication of this disease. Many other fungi which belong Fig. 7. — UstuUna zonata ; mycelium between the wood and the bark, x J. to the same class as UstuKna form black hnes in wood, and the majority of them are merely saprophytic. 60 THE RUBBER TREE The fructification of the fungus (Fig. 8) is usually produced in profusion at the base of the stem, generally before the tree is dead. The fungUs emerges through the bark as a short, white column, one or two millimetres in diameter, and spreads out in all directions flat on the surface of the bark, being attached to the bark only at the point of origin. It thus forms a flat plate about four or five centi- metres in diameter, but several may arise side by side and fuse into a continuous plate covering a large area of the Fio. 8. — Ustulina zonata ; fructification, x J. base of the stem. These plates are at first white and soft, but soon become grey or greenish-grey. In the tj^ical form they are generally concentrically zoned or corrugated. They then harden and become purple-grey, and finally weather to black ; in these later stages they bear scattered, miuute, black, slightly elevated points. After the plates have become hard they are at &st white internally, with a single layer of dark, oval, or globose cavities (Fig. 9) ; later they become black internally, and more or less hollow. When old they are brittle, and easily crumble to pieces when handled. They are usually not more than about two milli- metres thick. ROOT DISEASES 61 Though the fructification is, in general, more or less flat when it grows on the bark of Hevea, it may assume other forms, especially if growing on an irregular surface. At the base of the tree it often grows over irregular bark, or even over soil, etc., and is then thrown into irre- gular undulations, and may lack the concentric zoning. Its crusty, brittle tex- ture is a good distin- guishing character. It differs from most ^ „ „ ,. . , , „ J. ,1 ,^ 111 J?IQ- 9- — Ustuhna zonata ; section of fructification. of the other black, x6. brittle, encrusting fungi which are encountered on a Kubber estate, in that it is only attached to the substratum at one point, or when several fructifications have fused together, at a few scattered points. Consequently it can readily be detached whole from the bark. On the other hand, most of the other fungi which form black crusts are attached over their whole under-surface and cannot be lifted off. TJstulina zonata produces two kinds of spores. The first appear when the plate is in the white stage, and are borne on erect stalks closely packed together over the whole surface. These are consequently borne superficially and can easily be blown about by the wind. The second kind of spore is produced in the oval cavities already described, and, when ripe, is extruded in minute black masses through the mouths of the cavities, which are the black points on the surface of the mature plate. Brooks in 1916 suggested that, in Malaya, the fungus began to grow on decayed stumps and spread from one tree to another by contact of diseased roots with healthy ones. But he pointed out that on some of the older estates on which the disease had been found, very few stumps remain, and that it is therefore hkely that there are other means of infection. He stated that some of the trees attacked by TJstulina had previously been attacked by white ants, and thought it might be probable that this disease might fre- quently follow an attack of those insects. In the same 62 THE RUBBER TREE chap. year Sharpies stated -that the fructifications had been found on jungle stumps left after burning. The prevalence of UstuUna zonata as a root disease of Tea is due to the practice of growing Grevilleas through the Tea, and felling them when they have grown too large. The fungus develops on the Grevillea stump and travels down its lateral roots, passing on to any Tea root which happens to be in contact with the Grevillea roots. To a lesser extent the same happens when Alhizzia moliiccana is felled, but another root disease is more usual in that case. The first case of UstuUna as a root disease of Hevea in Ceylon was in an old Tea field where the Tea had been abandoned and allowed to die out. In that case the UstuUna undoubtedly spread from the dead Tea roots to the Hevea. In another case Alhizzia and LunumideUa had been planted as shade trees along the roadsides of a Tea estate, and the Tea was subsequently interplanted with Hevea ; after some years the shade trees were cut out, and in mmierous instances the course of their lateral roots was marked by a Kne of dead Tea bushes and one or two Hevea, either dead or attacked by UstuUna. On anpther estate Alhizzia had been planted at the same time as the Hevea, and cut out later ; many Hevea trees were subsequently attacked by UstuUna, and clear cases of infection on the tap root just below the laterals were demonstrable, where a dead lateral root of the Alhizzia was in contact with a Hevea. UstuUna has also been found to develop on Cacao stumps where Cacao interplanted among Rubber has been cut out, and on Hevea stumps left after thinning out. The prevalence of UstuUna root disease in Ceylon during the last five years must, to a considerable extent, be attributed to the practice, which was common in the early days of thinning out, of leaving the felled Hevea logs to rot among the standing Rubber. UstuUna zonata is one of the commonest fungi on rotting Hevea logs in Ceylon, especially when they are six to twelve months old. The numerous fructifications produce countless numbers of spores which can infect the Hevea, and it is possible that the fungus may pass from a decaying Hevea log to a living root on which the log may happen to rest. As noted in the Federated Malay States, cases of UstuUna ROOT DISEASES 63 root disease occur on Rubber in fields where old stumps have disappeared, or have been removed, and all felled timber cleared up. There is seldom any way of estimating how long a tree has been attacked, and, as the disease is usually a slow one, some of these infections may date from the time when stumps or timber were present. But there is no reason to doiibt that Ustulina zonata will be able to attack Hevea of any age, more especially through wounds, by means of wind- er insect-borne spores, independently of the presence of any jungle or Hevea stumps or rotting logs. That spore infection does happen is evident from the attacks of Ustulina on the stem, several feet above ground, without any occurrence of disease in the roots. The treatment of cases of root disease, caused by Ustulina zonata should follow the usual rules for root diseases in general. Dead trees and any neighbouring dead stumps, whether jungle stumps or old Hevea stumps left after thinning out, should be dug up and burnt. Care should be taken to follow up and extract the laterals as far as possible, as the disease spreads from tree to tree by contact of diseased roots with healthy ones of neighbouring trees. The fungus has not been found to produce free strands of mycelium in the soil, but, nevertheless, it is best to trench round the affected area and so sever the roots of surrounding trees which run into the latter. The cut ends of healthy roots on the outer wall of the trench should be tarred. Lime should be forked in over the enclosed patch. When the disease is discovered as a collar rot there is generally a desire to retain the tree until it dies, as it usually yields latex in normal quantity, or more than normal quantity, on the unaffected side, and above the diseased area. In that case any diseased lateral root and any neighbouring stump should be dug up and burnt, the diseased wood and bark at the base of the stem cut away, and the wound tarred. Modern methods of tree surgery might be applied in such cases, and the hole filled up with cement concrete or brickwork to give support to the stem. Such measures have not yet been extensively tried in the tropics, and it is doubtful how far they can be employed, and whether the tree will survive long enough to make the operation profitable. But if the tree is not to be treated it should be removed. Leaving a diseased 64 THE RUBBER TREE chap. tree untreated until it dies is to be deprecated, as it will bear fructifications which will produce innumerable spores and possibly infect others. The periodic collection of fructifica- tions is impracticable in the case of UstuUna, which forms its fructification rapidly and bears spores in its early stages. The removal of felled Hevea is now general, and it is no longer necessary to emphasise the necessity of getting rid of that source of UstuUna and other parasitic fimgi. Sphaebostilbe repens, B. and Br. This root disease was first discovered in Ceylon in 1907. Since then it has been found in that country on several occasions, but in no case has it caused any widespread damage. It has also been reported from Malaya, where it is said to be by no means rare on old Rubber. In the fijst case observed, it killed three large trees about twenty-five years old. These stood in a patch of undrained sour soil, between a set of cooly lines and a factory, where their surface roots were constantly being damaged. This area was used as a storage ground for firewood, and it is most probable that the fungus was brought with the dead wood and attacked the damaged lateral roots. In another case a single tree about twelve years old, which stood in swampy ground at the side of a stream, was killed. In each of two other instances, an old tree, again in swampy soil, succumbed to its attack. Judging from these cases, the disease would appear to be most frequent in swampy or sour soil, but in another instance it killed young trees, about two years old, in average plantation soil, and several further cases have been noted under similar conditions. The records show that in Ceylon it is not confined to any particular district. As is natural, seeing that rubber is chiefly a low-country product, most of the cases come from the low country. This, however, does not indicate that they are from swampy areas, as, in Ceylon, low-country Rubber is principally on hilly or undulating land. But cases also occur up to 2000 feet, about the maximum elevation at which Rubber is grown in Ceylon, and the fungus has been found as a saprophyte in various districts up to that elevation. In Malaya the disease was recorded by Richards in 1913 ; ROOT DISEASES 65 and in 1914 Brooks found that a considerable number of trees were affected by it. According to Brooks the disease is by no means rare in old Eubber planted on low- lying land in Mal- aya, having been found iri Northern Perak, in the dis- trict round Teluk Anson, and in the coast lands of Selangor. Only a few trees on un- dulating land were seen to be at- tacked by it. The mycelium of the fungus at once distinguishes this disease from those caused by Fomes lignosus and Fomes lamao- ensis, but it is not immediately evident like that of the two latter species. When the root is dug up the cortex is found to be decayed, but there is no external mycelium. But if the cortex is re- moved, black or red flattened strands are seen running over the surface of the wood (Fig. 10). The inside of the cortex and the outer layers of the wood are usually a deep blue, or purple, when fresh, and have a particularly foul smell. The blue colour, however, is not confined to roots attacked by this disease, but sometimes occurs on tap roots killed by UstuKna, below the level at which the UstuUna has attacked them. The smell, too, is not a distinctive sign of this disease, Fig. 10. — SphaerosHlbe repens ; mycelium on wood of root. 66 THE RUBBER TREE chap and is probably caused, not by the SpTiaerostilbe, but by the action of secojidary organisms on the cortex or wood. The mycelial strands are usually about two millimetres broad, but they may reach a breadth of five millimetres. At first they are red externally and white internally, but when the root is much decayed the strands decay also and become black. If the fungus is living the strands are fairly thick and stand out prominently above the wood, but ' on old decayed roots they are little more than a black film on its surface. When the cortex is stripped off the wood the strands are often split lengthwise, especially when they are in a living condition, and half remains on the cortex and half on the wood. The white inner tissues of the fungus are then exposed, and these often present a fern-like arrangement. These strands are not simple cords composed of hyphae lying side by side, such as occur in Fomes Ugnosus, but have a definite cortex, different in structure from the inner tissue. They constitute what are known as rhizomorphs. Figure 10 indicates one way in which the fungus may attack a tree. The mycelium enters the smaller roots and advances along them until it reaches the larger. There its rhizomorphs spread out and branch, and these branches run between the cortex and the wood until the tap root is reached. On the tap root it forms similar strands, but at the collar it may form a continuous red sheet, between the wood and the cortex^ as before. The point on the figure from which the strands radiate is the place where a small root, about two millimetres in diameter, joined the larger root. Sometimes the striands run in the cortex, beneath the thin papery layer which forms the external covering of a Hevea root and which can usually be peeled off when the root is dead. The decay of the root is brought about by fine hyphae which are given off by the rhizomorphs and permeate the wood and cortex. The fungus may ascend from the collar for some distance, two or three feet, up the stem, and the rhizomorphs may occur there either in the bark or between the bark and the wood. A stronger development of mycelium is shown in No. 7 on Figure 11. In that case the rhizomorphs are much broader, and they have fused behind into a continuous ROOT DISEASES 67 sheet. The outer surface of the rhizomorphs is marked with a peculiar herring-bone pattern ; this occurs also on the narrower rhizomorphs which are usually found in Hevea, but it is not so easily recognised there. This particular specimen was found between the wood and the bark of a decaying Dadap log (Erythrina Uthosperma). When the bark was separated from the wood these thick strands were often split horizon- tally, and the white internal tissue then presented a fern-like appearance. The patch of mycelium was over a yard in length and about eight inches broad, the separate rhizomorphs being evident only at the margin. The fructifications of the fungus are produced on the diseased tissues, or on the rhizomorphs when the latter have become exposed through the cracking or weathering ofi of the bark. The fixst form of fructification has been observed by Brooks on clayey soil lying in contact with diseased roots. The fructifications are of two kinds,- — a conidial form, in which the spores are borne free at the apex of short stems, and a perithecial form, in which the spores are enclosed in perithecia. The conidial fructifications are the first to appear. They take the form of short, erect, red stalks from two to eight millimetres high, and half to one millimetre in diameter, surmounted by a white or pinkish globose head, one to one and a half millimetres in diameter. Though individually small, they occur in large numbers and are consequently fairly conspicuous. The stalk is hairy at first, but becomes glabrous in the lower half later (Fig. 11). There are two common conidial fructifications often found on Hevea which might at first sight be mistaken for that of SphaerostiJbe repens. One of these, Stilbum nanum, Massee, is frequently found on Hevea twigs. The other, Stittnim cinnabarinum, Mont., often occurs in large numbers on dead Hevea bark, sometimes accompanied by minute red spheres, which are its perithecial stage, Megalonectria pseudotrichia, Schw. Both these have red stalks and red or pinkish heads, like minute pins, but their stalks are smooth, not hairy, and they can easily be distinguished with a hand lens from the conidial stage of Sphaerostilhe repens. The second or perithecial stage of the fungus follows the first stage on the same area, but in many cases it does not 68 THE RUBBER TREE "hap. appear to be produced. The perithecia are small dark red bodies, rounded below and conical above, about 0'6 mm. high, and 0-4 mm. in diameter (Fig. 11). They are crowded together on the bark, at the edge of the mycelium if that is exposed, or round the bases of the old stalks, or even along the stalks. They are identical in structure and appear- ance with those of a Nedria, but as the conidial stage differs from that of a Nedria, the fungus is placed in a different genus. Sometimes the rhizomorphs of Sphaerostiihe repens become superficial, i.e. run along the surface of the host plant, especially when the fungus is only saprophytic ; the conidio- phores and perithecia are then borne anywhere along them. Sphaerostiihe repens was first collected by Thwaites at Peradeniya about the year 1868. His specimens grew on Jak (Artocarpiis integrifolia). Whether it was parasitic or saprophjrtic is not recorded, but judging from later occur- rences it was probably only saprophytic. In 1908 a healthy Jak tree in the Botanic Gardens was felled, and soon after- wards Sphaerostiihe repens developed in abundance on the chips which were left lying round the base of the stump. It was found in 1906 on a decaying Dadap log about a foot in diameter. The tree was quite sound when felled, so that the fungus in this case also was only saprophytic. Specimens were sent in in 1906 on the rhizome of arrow- root {Maranta arundinacea). In this case it was undoubtedly parasitic. The rhizomorphs had apparently spread through the soil to the arrowroot, and, after growing for some distance along the scale leaves, had penetrated into the rhizome, where they formed a number of more or less parallel strands running lengthwise through it. The rhizome was decayed along one side, but in general the tissue surrounding the rhizomorphs appeared quite soimd. The extension of the rhizomorphs would appear to depend on the supply of food from behind, not on food obtained from the immediately surrounding tissues, at least in the early stages of extension. This fungus has also been found to attack the roots of the Papaw. In advanced stages the soft tissue in the centre of the stem is, at the base, converted into a pulpy rotting mass, and the rhizomorphs form a wide-meshed network which can be extracted in large sections. ROOT DISEASES 69 Conidia {i.e. the first kind of spore) sown on cut surfaces of arrowroot developed the first stage of the fungus in seven days and the perithecial stage id twenty-one days. Brooks, in Malaya, attempted infection experiments with Sphaetostilbe repens on Hevea. Eoots of seedling Hevea in pots, and of four-year-old trees on hilly land, were inoculated with material of the fungus from pure cultures. A block of Hevea wood on which the mycelium was growing, or mycelium from an agar culture, was placed against a root, which iu some cases was wounded and in others not injured. Sixteen plants ■ were treated, but after nearly five months none of them showed signs of infection. Brooks considers that this negative result points to the possibility that some condition which disposes to susceptibility must exist before the fungus can invade the roots of a Eubber tree, and points out that bad aeration of the soil, consequent on deficient drainage, may be a factor in inducing the requisite condition for the fungus to enter. As previously stated, the fungus develops freely on small pieces of Jak wood, and it has been found to spread to Hevea from decaying Jak stumps. In this respect it resembles Fomes lignosus, and provides an additional reason for the removal of Jak stumps. It also occurs on felled Dadap logs, and has been found to cause root disease of Derris robusta, so that it is probable that it may attack members of the order Leguminosae in general. In the first case recorded the fungus was probably introduced with firewood, i.e. miscellaneous jungle timber. Dead trees must be dug up and burnt, as much of the roots as possible being extracted, especially the laterals. Any neighbouring stump should also be dug out, and all pieces of wood collected and burnt. Small pieces of wood are quite sufficient to provide a suitable habitat for the fungus. The affected area should be surrounded by a trench about two feet deep, and the groimd dug over and dosed with lime, which should then be forked in. 70 THE RUBBER TREE ElG. 11. details of the fungus. No. 1. A group of oonidiophores. x 2. No. 2. Tip of a hair from the stalk, x 350. No. 3. Conidiiferoua hypha from the apex of the oonidiophores. x 500. No. 4. Conidia. x 600. No. 5. Perithecia on an old oonidiophore. x 6. No. 6. Groups of perithecia on a horizontal rhizomorph. x 2. No. 7. Bhizomorpns from dadap. No. 8. Cross section of a rhizomorph ; outline only, x 2. No. 9. Cross section of the cortex of a rhizomorph, magnified. No. 10. .Cross section through the rhizome of arrowroot attacked by Sphaerostilbe ; the dark lines are the sections of the rhizomorphs. ROOT DISEASES 71 EooT Disease op " Stumps " {Botryodiphdia Theobromae, Pat.) In several cases in Ceylon Hevea stumps which had been planted out under favourable conditions failed to grow. Generally the plants made no growth whatever, but occasion- ally some developed a green shoot about six inches long and then died. They were usually sent in as examples of the damage done by white ants, because the tap root, as a rule, had been partly eaten away, all the cortex having disappeared, and only an irregular spindle of wood left. In practically every case it was determined that death was due to Botryo- diphdia Theobromae, the fungus which causes Die-back. When the root was split open black streaks were found running longitudinally down the wood. This discoloration is due to the mycelium of the fungus, which is dark-coloured when mature. The cortex was also blackened internally (when present) and contained the characteristic fructifications of the fungus ; and in some cases these fructifications formed large black cushions at the points of origin of the small secondary roots after the latter had disappeared. In these cases the fungus had entered the plant, not at the top as in Die-back, but either below ground or at the collar. It is probable that, in the majority of cases, its entrance was facilitated by injuries inflicted during planting, but in one case at least it would appear that the fungus was able to attack uninjured plants. . In general, further loss was avoided by liming the holes where the plants had died and supplying with basket plants, but in one case some of the supplies died from the same cause. The evidence afforded by other crops appears to show that this fungus can live in the soil, and can attack the roots of umnjured plants ; it causes a serious root disease of Tea in Ceylon. This disease in Ceylon proved worse on Rubber planted among Tea and on old chena land {i.e. jungle land previously cleared for temporary native cultivation) than on land which was newly cleared of virgin jungle. The plants attacked were usually about two inches in girth. It was recorded from Ceylon and Burma in 1906, and in one instance in the latter coimtry sixty per cent of the stumps were killed. In 1909 72 THE RUBBER TREE chap. it was recorded from the Federated Malay States, the stumps attacked being about three inches in girth, and eighty per cent being killed. PoLYPOBUs BuauLosus, Lev. This fungus was found by Brooks in Malaya under condi- tions which appeared to iudicate that it was the cause of a root disease, but it has not yet been definitely decided that such is the case. It was observed on several occasions growing at the collar or upon exposed lateral roots of diseased Rubber trees, only on trees which were in tapping, and appeared to be more frequent on badly-drained, low-lying estates than on undulating land. The bark and wood near the fructifications was invariably decayed, the foliage of the affected trees became thin, and the branches died back. One tree which was severely attacked had been previously invaded by white ants. The fructifications of the fungus are bracket-shaped, thin, and only an inch or two in diameter, but they occur in numbers one above the other, and form large groups several inches across. They are fleshy when young, and become leathery when old. The upper surface is smooth, brownish, and concentrically zoned ; the lower surface is white at first, and becomes yellow-brown when old. It differs from Fomes Ugnosus in its smaller size, the colour of the pore surface, and its thinner substance. It is advised that trees which are apparently affected by this fungus should be treated as for Fomes lignosus. Wounds on exposed Lateral Roots Wounds on exposed lateral roots are very common on old Rubber in Ceylon. They are confined to the upper surface of the roots, along which a continuous wound may extend for several feet. It has been suggested that they are caused by stones which are washed down the hill-sides, but that sugges- tion would seem to be negatived by the fact that for a considerable time the dead cortex remains intact within the wound. Another suggestion is that they are caused by coolies walking over the roots. It has to be borne in mind ROOT DISEASES 73 that tke. roots are not developed on tlie surface, but are brought to that position by their growth in thickness and by the loss of soil through wash, and it is possible that this unnatural exposure may be the primary factor in the causa- tion of these wounds. The first stage in their formation is the death of the cortex over the upper surface of the root. This occurs in varying lengths, and may extend from side to side of the exposedpart, or be confined to a narrow strip down the middle. Growth of the root in thickness is then arrested over this dead area, which is consequently surrounded by a more or less swollen rim or callus. The dead bark persists for some time within the wound, but ultimately cracks and disappears. The wood which is then exposed is black on the surface and brown within, and, in old wounds, this region of discoloured dead wood may extend half-way through the root, being separated from the healthy wood by a red-brown line. The wood is at first quite hard, but after prolonged exposure it breaks up and leaves a hoUow in which rain-water collects. Occasionally these wounds heal up naturally. Generally, however, they gradually spread along the root in both directions, and widen until they reach ground level on either side. In long-standing ' cases the edges of the wound are often margined by a series of ridges, the successive callus borders which have been killed as the wound broadened. The wounds extend along the root right up to the trunk, but they have not been observed to ascend the stem. It is, however, very probable that the gradual decay of the wood will proceed from the root into the stem without giving any outward indication. The death of the cortex, which begins the injury, may take place over a large area in a short time, and the extent of this decides the size of the original wound. The subsequent enlargement of the wound takes place very slowly. "V^ere an exposed lateral root dips below the surface and reappears further on, wounds may be formed on both the exposed parts, but the bark on the buried part of the root is, as a rule, healthy, though the discoloured wood may extend within the root from one wound to the other. The fungus which is generally present on the dead bark is Aposphaeria Heveae. This is common on dead Hevea 74 THE RUBBER TREE chai branches aiid felled logs, and it is very doubtful whether it is parasitic. It forms black, slightly projecting lines in the cracks of the bark. Up to the present no effect on the general health of the tree has been observed as a result of these wounds, and estates, as a rule, have not undertaken any treatment of them. It would be advisable to try to prevent further decay by painting them with Brunolinum or Jodelite, and subse- quently with coal tar. If the decayed wood is scraped out care should be taken not to leave a hollow in which water can lodge ; it may be necessary to cut away part of the healthy tissue on one side of the wound to ensure drainage. Whether it is advisable to terrace round the trees and cover the wounded roots with earth is an unsettled question. It is possible that under such conditions the growth of caUus might be more active, and the wound might heal. On the other hand, there is perhaps a greater probability that the decay of the wood might be accelerated, and that the roots might be attacked by Vstulina. If terracing is tried with this end in view the wounds should be tarred and the tar allowed to dry first. In young plantations terracing should be adopted as soon as, or before, the lateral roots are exposed. It remains to be seen whether the tree can compensate for the loss of these roots by producing others at a lower level. SUMMAEY ROOT DISEASES FoMES LiONOSVs, Klotzsch Identification. — Wtite, yellowish, or reddish strands on the roots (Fig. 1 ; Plate II., Fig. 4) : young strands feathery (Fig. 2) ; all firmly attached to the root. Decayed wood soft, often wet. Fructification, a red-brown bracket, concentrically zoned (Plate I., and Plate II., Fig. 1) ; lower surface orange, then red-brown (Plate II., Fig. 2) ; when broken the section shows two colours (Plate II., Fig. 3). Occurrence. — ^In clearings the fungus starts on decaying jungle stumps, and spreads from them to the roots of the Hevea. It similarly starts from Hevea stumps left after thinning out, abandoned Tea, Cacao stumps, and stumps and logs of the thorny or smooth Dadap. Treatment. — See pp. 40, 41. ROOT DISEASES 75 Brown Eoot Disease {Fames lamaoensis, Murr.) Identification. — Roots encrusted with sand, earth, and small stones, fastened to the root by fine brown mycelium which is col- lected here and there in brown masses. When old a black crust develops over the brown masses (Fig. 3). Wood permeated, some- times honeycombed, by brown lines or bands (Plate II., Figs. 7 and 8) with sometimes a few thin black lines. Fructification rarely developed — a very hard, purple-brown bracket (Plate II., Fig. 10), pale or dark brown in section (Plate II., Fig. 9). Occurrence. — Spreads to Rubber from jungle stumps, Hevea stumps, etc., by contact. Very common on old Cacao land where the Cacao has been cut down. Attacks cultivated trees and shrubs of all kinds, but progresses slowly, and does not cause great damage except where Cacao has been cut out of mixed Hevea and Cacao. Treatment.— ^^e pp. 24, 49. Red Root Disease {Poria Jiypobrunnea, Petch) Identification. — Red strands on the exterior of the root (Plate v.. Fig. 4) ; these turn black when old. Red sheets and plates in the decayed wood (Plate V., Fig. 3) ; these turn brown when old. Fructification, a flat plate, white or ochraceous at first, then red-brown, finally slate coloured (Plate II., Fig. 5) ; in section blackish- brown (Plate II., Fig. 6). Occurrence. — In new clearings spreads to Hevea from jungle stumps. The red strands can travel free through the soil for a short distance. Common in old Rubber on rotting Hevea logs. Treatment. — See pp. 24, 55. Clearing up all timber is essential. Wet Rot (Fomes fseudo-ferreus, Wakef.) IdentifiKiation. — ^Diseased roots wet ; in advanced cases con- verted into a jelly-like mass. Sometimes a very dark, reddish skin on the exterior of the root ; this can be peeled ofi when fresh. Brown lines or plates, or broad brown bands, in the wood. Fructification rare. Occurrenee. — ^Develops on jungle stumps, and passes to Hevea roots by contact. Only known to occur in Malaya. Treatment. — ^As for root diseases in general. Complete removal of stumps necessary. 76 THE RUBBER TREE ohap.h USTULINA ZONATA, L6v. Identification.- — ^No external myceliuin. Decayed roots often dry, and usually permeated with thick black lines (Fig. 4). White or brownish fans of mycelium between the bark and the wood (Fig. 7). Fructification formed at the collar, a flat or undulating plate, at first white, then greenish, then purple-grey, finally black (Fig. 8). When old the fructification is crust-like and brittle. Plates often con- centrically zoned. Occurrence. — ^Attacks Hevea from abandoned Tea, Hevea stumps, Alhizzia stumps, etc., by root contact, and by spore infections on wounds. The fructifications occur abundantly on decajdng Hevea logs. Treatment. — See pp. 24, 63. Rotting Hevea logs must be cleared up. SpsAEROSTiLBE BEPENSf B. and Br. Identifijcation. — Red strands of mycelium between the wood and the bark ; these turn black when old (Fig. 10). Root usually bluish- purple and foul-smelling. Occurrence. — Has been found on rotting Jak {Artocarpus integri- folia) and Dadap {Erythrina lithosperma) logs. Attacks Papaw, Arrowroot, and Tea. Probably spreads to Hevea from decaying timber. Treatment. — See pp. 73, 74. Wounds on exposed Lateral Roots Cause unknown. Scrape out decayed wood ; paint with Bruno- limun or Jodelite, etc., and then tar (see p. 74). CHAPTER III LEAF DISEASES In 1911 the statement that plantation Eubber was not subject to any serious leaf disease was an accurate summary of the conditions then known to exist. Several diseases were known, but none of them had been found to cause any notable damage. Since that time, however, the situation has changed completely, and among the new leaf diseases which have made their appearance are two which are capable of becoming a serious menace to the rubber industry. One of these is at present confined to South America, where it occurs in all rubber-growing countries, and is reported to have become so virulent in at least one of them that it is doubtful whether Hevea can be cultivated at a profit. The other, which occurs in Ceylon and India, and probably in Java also, partly defoliates the trees in wet years, but is so largely dependent upon climatic conditions that, in Ceylon at least, it is not epidemic annually. If, however, a series of consecutive years of heavy rainfall should happen, and this abnormal defoliation occur annually in consequence, the resulting damage would become very serious. The occurrence of these two diseases should serve to dis- prove the theory, which has previously been shown to be a fallacy, that because Hevea sheds its leaves annually it is less liable to be attacked by leaf disease or wiU sufier less damage when attacked than Tea, Cacao, or Coffee, which are ever- green. In many cases, and the South American leaf disease is a case in point, the fungi which attack the leaves of decidu- ous trees pass through two (or more) different stages in their life-history. In the first stage they produce spores which serve to convey the disease immediately to other leaves, while in another stage they produce different spores more 77 78 THE RUBBER TREE chap. resistant to drying or to climatic influences. This second stage is often passed in the dead fallen leaf, and its spores carry the fungus over the period when the tree is leafless. Thus the actual defoliation does not necessarily involve the destruction of the fungus ; and, in actual fact, the serious leaf diseases of deciduous trees are more numerous than those of evergreen trees. The South American leaf disease also brings into prominence another phase of the life-history of the Hevea tree, which renders it more liable to the continued attack of a leaf disease, viz. that as all the trees do not " winter " at the same time, there are always some in leaf, and capable of transmitting any disease to the new foKage of the others. And there is the fuxther point that the leafless phase is of such short duration that many spores of the first stage of a fungus might survive it. There is general agreement among mycologists, who have had actual experience of Rubber estates, that the method usually adopted for the control of leaf diseases, viz. spraying with a fungicide, is impossible in. the case of tappable Hevea. The various methods which have been proposed for combating the more serious leaf diseases of Hevea are quoted imder the special diseases concerned. The South American Leaf Disease {Fusicladium macrosporum, Kuyper) The most serious leaf disease of Hevea which has yet been recorded is at present confined to South America. It was first discovered in the Amazon Valley, but has since made its appearance in Trinidad and British Guiana, and has done great damage in Surinam. The disease appears first on the young leaves, from three to five days old, before they have attained their full size, and causes somewhat translucent olive-green or blackish-greeh spots, which are sometimes so numerous that the whole leaf blackens and shrivels up. When young plants are severely attacked their tops bear only blackened dead leaves. It may happen, however, that as the leaf increases in size the growth of the fungus does not keep pace with it, and the original spots may then dry up and split or fall out, leaving holes in the leaf or lesions extending from the margin. This in LEAF DISEASES 79 perforation and tearing of the leaves occurs most generally on old trees. Tlie fungus also attacks the leaf stalks and green stems, which become swollen in the diseased zone, the swell- ings subsequently cracking and forming small cankers ; these swellings are at first green, but become black later. The spots on the leaf are at first translucent. They then become dark green, or olive-green, and velvety, owing to the developinent of an enormous number of minute erect stalks (conidiophores), on which the spores (conidia) of the fungus are produced. On old spots the centre may be yellow, the velvety covering being confined to the margin. On the leaf- stalks and twigs the fungus forms a superficial weft of hyphae from wliich the conidiophores arise. The form described above is the first, or conidial, stage of the fungus. A second (pycnidial) stage appears round the edges of the holes on the older leaves in the shape of minute black points, sometimes so close together that they form a complete ring. A third (perithecial) stage appears on old leaves one to two months after they are full-grown ; in this stage the fungus causes small brownish areas, scattered over the leaf, and the fructification is produced as a black circular patch, up to four millimetres in diameter, in the centre of each brown spot. The disease attacks old and young trees alike, but it does most damage to young foliage. Stahel, who has investigated the disease in Surinam, states that the spores of the second and third stages are of minor importance in the pro- pagation of the disease, and that it is spread chiefly by the conidia. The conidia germinate in two hours if placed in water, and, if sown on an immature leaf, the germ tubes have penetrated into the leaf in ten hours. But if allowed to dry they die in fifteen hours. According to Stahel, the disease is perpetuated by the continuous production of spores (conidia) on immature leaves. Hevea produces new shoots several times in the course of a year, and this occurs at different times on different trees, or even on different parts of the same tree. Hence there is always some young foliage present on which the conidial stage can develop and so ensure the continuance of the disease. He therefore advises that, for a period of three or four weeks, all the new shoots which appear should be cut off, 80 THE RUBBER TREE ™^f so that the Fusicladium spores will not be able to fall on leaves in a condition fit for infection, and will consequently die. In that way the fungus will be eradicated. Stahel recognises that the ascospores, i.e. the spores of the third stage, which develop on old leaves, will, if they alight on young leaves, give rise to the Fusicladium again, but he holds that, as the number of ascospores is small, the infection from that source will not be extensive, and can be met by another pruning. It is recommended that the young shoots should be cut ofi with a Cacao knife, and it is estimated that a cooly should be able to finish one or two large trees, or more small ones, in a day. It is, of course, essential that all plantations should carry out this measure at the same time, otherwise a planta- tion which has been treated will be reinfected from its neigh- bours. Judged by experience in the East, the method would scarcely appear to be practicable, and the reasons on which it is based do not impress one as possessing a very high degree of probability. Bancroft, after visiting Surinam m. 1916, described the condition of the Rubber estates there as follows. " [The disease] appeared in epidemic form on certain plantations in 1914, affecting principally the young trees. Subsequently it spread to other plantations, and it is now present on every estate on which Hevea is grown. On th.e majority of estates the trees are badly affected and are dying in large numbers, some estates having lost in certain areas one-third of the total number of trees. Trees of all ages are affected, and there appears to be no sign of the disease diminishing in any respect. Tapping operations have for the most part been suspended owing to the great reduction in the yield of latex. Several cultivators who possess Hevea mixed with coffee intend to remove the Hevea and to cultivate coffee only." The disease appeared in British Guiana about the same time as in Surinam, i.e. about 1907. In 1917 it was stated that a fair proportion of the cultivated Hevea was only slightly affected, and on some plantations where the disease had been prevalent it had shown signs of diminishing. On the other hand, on other plantations there was no indication of any reduction of the disease. Trees supposed to be situated Plate III. r.KAF AND STKM DISEASES m LEAF DISEASES 81 fifty miles from any other known Hevea trees had become infected. In Trinidad the disease first became noticeable in 1916, when considerable defoliation occurred on several estates in widely different parts of the island. In the following year it was more generally distributed, and a number of trees had been killed by the repeated defoliations. The available evidence indicates that this disease is present wherever Hevea is cultivated in South America, and that it occurs on many, if not all, of the species of Hevea growing wild in the jungle. It has caused the greatest, amount of damage in Surinam, where it is now question- able whether Hevea can be cultivated at a profit. In addition to the removal of diseased shoots spraying has been recommended as a remedy, and it has also been suggested that some system of smoking, which would cause the trees to shed all their leaves, might get rid of the fungus. The latter method, however, would probably not have the desired result, if, as stated by Kuyper, the conidia are produced on green stems as well as on the leaves. But it does not seem likely that it will be possible to eradicate the fungus so long as the cultivated trees are liable to in- fection from the wild Heveas. The names which the fungus has received are fairly numerous. The perfect or third stage was named Dothidella Uki by Hennings in 1904, and the conidial stage Fusicladium macrosporum by Kuyper in 1911. Specimens of the conidial stage sent to Kew from British Guiana were named Passahra Heveae by Massee. Stahel prefers to regard the conidial stage as a Scolecotrichum, and has named the perfect stage Melano- psammopsis Heveae. Bird's-eye Spot {Helminthosporium Heveae, Fetch) This disease frequently attacks the leaves of nursery plants, but has rarely been found on older trees. The nursery plants are usually afiected when they are about three or four feet high. The fungus causes minute spots which are at first purple, but as they increase in size they become white and semi-transparent, surrounded by a narrow purple-brown 82 THE RUBBER TREE ''^^ border (Plate III., Fig. 4). The mature spots aie generally circular. As a rule, they are small, not exceeding five miUi- metres in diameter, but they may occur in large numbers on a single leaf. They are scattered all over ^e leaf in no particidar order. The fungus breaks through the epidermis, and appears on either side of leaf in the form of minute black points on the white spot. Each of these points is a cluster of minute stalks on which the spores are produced, or it may be only a single stalk. The spores are, for fungus spores, comparatively large (up to a fifth of a miUimefece long), and they may often be detected with a simple lens, as long, narrow, brown, and shining objects lying on the surface of the white spot. This disease has been known in Ceylon since 1905, and it is periodically reported on nursery plants. The young plants are not defoliated by it, and they do not appear to sulEer any damage. As a rule, it has caused so little injury that no treatment has been considered necessary. Should it prove serious, the plants should be sprayed with Bordeaux mixture. The disease has also been recorded for South India and Malaya. Shot-hoi^ Leap Disease The name " Shot-hole " disease is usually given to a leaf disease which causes small circular holes in the leaf. One such disease on leaves of Hevea has been described by Yincens, who observed it on the leaves of nursery plants at Para. It formed small circular spots not exceeding five millimetres in diameter, more or less translucent, witihi a slightly raised violet or brown rim, surrounded by a pale zone. \\Tien the spots attain their full size the central dead area dries up and falls out, leaving a circular hole margined with brown. The spot resembles tiiat caused by HehnitOhosporium Heieae, but it is usually larger, and in the case of the Helminthosporiuin the centre does not, as a rule, disappear. In general, only a few leaves are attacked, and the spots are not numerous. It has, however, been observed in a more serious form on young, poorly grown Hevea, imder dense shade. The leaves in that case were literally riddled with holes. in LEAF DISEASES 83 Several fungi have been found on these spots, but it has not been decided which of them causes the disease. The species which occurs most frequently is a Scolecotrichum, Scolecotrichum Heveae, which Viacens considers the principal agent. Other fungi which are also found on them are Fusarium Heveae, Aposphaeria Ulei, and Zygosporiwm paraense. Catacauma Huberi (P. Henn.), Theiss. and Syd. This fungus was originally found on leaves of yoimg Hevea at Para. According to Vincens, it is very common in the Amazon valley, but it does not cause any serious damage. It has not been recorded outside South America. Catacauma Huberi attacks full-grown leaves. It forms shining black crusts, up to a centimetre in diameter, on the under side of the leaves, with corresponding pale green patches on the upper surface. As a rule there is a central black crust, or stroma, from five to ten millimetres in- diameter, surrounded by a number of smaller stromata arranged round it in a circle, and separated from it by a pale green zone. Sometimes a second circle of small stromata appears round the first. The leaves do not appear to suffer to any notable extent from the presence of this parasite, which only kills the tissues below it very slowly. Those leaves which are strongly attacked, and covered with the stromata of the fungus, fall a few days earlier than soimd leaves. Kim Blights Three difierent fungi attack the leaves of Hevea and cause diseases which may be conveniently known as Eim Blights, since their effect is to produce a narrow white or brownish zone, about a centimetre wide, extending all round, or partly round, the margin of the leaf. Two of these diseases are so much alike in. general appearance that they can scarcely be distinguished from one another without a microscopical examination and determination of the fungus concerned. But though their effects are so similar, the fungi are quite different, and there is, as yet, no, evidence that there is any relation between them. The three diseases have been 84 THE RUBBER TREE ^^■ recorded from widely separated localities in Ceylon, and in no case have they caused serious damage. At present they are not generally distributed, but, as they have only recently been discovered, it is too early to generalise on their distribu- tion and effect. On a tree which has been attacked for some time the effect is very striking, as practically every leaf is margined with brown or white. But, according to the observations hitherto made, the leaves do not fall off before the normal wintering. AscocHYTA Rim Blight {Ascochyta Heveae, Petch) In the first stage of this disease the leaf shows numerous minute, yellowish spots, crowded together in groups which extend from the margin inwards between the veins. Some of the spots near the edge of the leaf then become reddish- brown, and merge into one another to form a dry, brown or greyish-brown patch, with a purple-brown border. These spots may be circular and situated near the margin, but more usually they extend from the edge of the leaf inwards towards the mid-rib between the veins. Finally, the dry spots extend along the margin and fuse with one another, so that the leaf is edged with a discoloured zone sometimes aU the way round. When old this zone becomes white or brownish- white. Its inner edge is not straight, but bends inwards between the veins, and it is limited by a narrow, red-brown or purple-brown line (Plate III., Fig. 5). When the dry margined zone is fuUy formed numerous yellow spots are still present in the green tissue towards the centre of the leaf, where they can easily be seen if the leaf is held up to the light. The fructifications of the fungus appear as minute black points on the white marginal zone. This disease attacks the leaves soon after they have matured ; and the fully-developed stage, when all the leaves of the tree are white-edged, may have been reached by June. In one small affected area it has been noted that the disease begins each year on one particular tree, and spreads from that to its neighbours. LEAF DISEASES 85 Sphaerella Rim Blight {Sphaerella Heveae, Fetch) The course of this disease closely resembles that of the previous one, the chief points of difference being that (1) the minute yellow spots become thickened, and purple or purple- brown before merging into one another ; (2) the line which bounds the inner side of the marginal diseased area is slightly thickened or 'elevated ; and (3) the zone itself becomes yellow- brown and finally grey. As in the previous disease, the fructifications appear as minute black points on the marginal band ; they are usually more clustered in this case than in the case of the Ascochyta. This disease has only been recorded once, in Ceylon, in 1917, a group of about half-a-dozen trees being attacked. GrUIGNARDIA RiM BlIGHT (Guignardia Heveae, Syd.) This disease differs from the two foregoing in that the dry marginal zone is, as far as is yet known, pale brown, and does not become grey or white. The affected part of the leaf forms a triangular patch at the tip with a flat base extend- ing transversely across the leaf, and runs down each side towards the base as a band, about one centimetre wide. The inner edge of this zone is purple-brown, and, as in the other rim blights, it bends in and out between the veins (Plate III., Fig. 3). There are no yellow spots in the leaf, but the purple- brown inner edge of the diseased area has a narrow yellowish- green band running along it on its inner side. This band is readily seen on holding the leaf up to the light. In the known cases of this disease in Ceylon it was particularly noticeable that the marginal diseased area never extended to the base of the leaf ; at most it covered two- thirds of the length. The injury caused was negligible, as it occurred on old trees, and on old leaves shortly before the time of leaf -fall. This disease has also been found in Singapore. 86 THE RUBBER TREE chap. Indeterminate Leap Spots Towards the close of its annual cycle the leaves of Hevea frequently become discoloured in irregular patches, or torn and mpre or less dilapidated. This is very liable to occur on trees exposed to strong winds, and in. Ceylon it appears to be more usual on Hevea iuterplanted through Tea, or on old Tea land, than on trees in other situations. One of the commonest appearances is a dry, brown, irregular area extending back from the tip of the leaf, while ia other cases similar patches extend from the margin inwards over the leaf blade, or both types may be present at the same time. These patches, as a rule, have no definite shape and no well-defined margin, hence they are best classed as indeterminate. When titey are old they often split or tear towards the mid-rib, and thus the leaves become ragged. Sometimes the tip breaks off altogether. How far these appearances are- to be attributed to the direct action of parasitic fungi is doubtful. Several species of fungi are to be found on such leaves, many of them only saprophytic, and in those cases in which parasitic fungi have been identified it has not been found possible to correlate these fungi with any definite type of injury. It would appear probable that the initial injury is the result of the action of the weather on the thin leaf, and that the fungi subsequently attack the damaged leaves. The leaf figured on Plate III., Pig. 6, illustrates the kind of injury in question. On the tree from which that specimen was taken the leaves bore irregular spots, one to two centi- metres in diameter, or large dead patches extending inwards from the margin, or similar patches extending backwards from the tip and often involving half the leaf. The dead patches were usually torn, and the diseased tissue had in many instances fallen out. Frequently the outer half of the leaf had disappeared completely. The affected areas were .dry, greyish-brown, with a purple-brown, somewhat diffuse margin. In this instance the fungi present were Colkto- trichum Heveae and Phyllosticta Heveae. In other instances in which similarly affected leaves have occurred the: fungus of Grey Blight, Pestalozzia palmarum, has been found on the dead parts of the leaf. The leaves LEAF DISEASES 87 bear grey or brown dry areas, extending back from the tip of the leaf for about two inches, or similar patches stretching inwards from the leaf margin, and angular spots of varying size scattered over the leaf, all bordered by purple-brown. The larger spots are usually broken, and the marginal diseased patches torn. In one case the dead areas at the tips of the leaves split longitudinally along the mid-rib. Rutgers has recorded a case, from Java, in which a similar effect was produced by Phyllosticta Heveae. The dead patches extended from the tips or from the margin of the leaf, and were brown, sharply defined from the sound green parts of the leaf. The plants affected were nursery plants, and in such cases there is considerable doubt whether the conditions under which the plants are grown do not largely influence the attacks of different fungi. Nurseries are usually shaded,, and conse- quently the young plants are grown in a highly humid atmosphere which favours the development of fungi and at the same time renders the plants more susceptible. In the case noted it was. determined that infection was only possible under conditions of high humidity, and then only on young leaves. This fungus was originally recorded from Java by Zimmermann. Brooks has also recorded the occurrence of a Phyllosticta on the margins of Hevea leaves in Malaya, causing a brown discoloration from the margin inwards. Inoculations showed that it could act as a weak patasite. "When the shade is removed from nurseries the young plants often appear to have been attacked in a wholesale manner by leaf disease. The leaves bear large, white, semi- transparent patches of varying shape and extent, dotted with minute, black fructifications of various fungi. As a general rule these fungi are not the cause of the dead patches, but have only developed on the leaves after they have begun to die . The patches are usually due to the action of sunlight on the young leaves. As the cadjan shade decays, it allows the sunlight to penetrate through the cracks and fall on the previously shaded, tender leaves, with the result that they are injured in parts only ; and feebly parasitic or saprophytic fungi subsequently grow on the injured spots. In some instances the leaves of young nursery plants have been found to be distinctly biu-nt, an effect which is to be attributed to 88 THE RUBBER TREE chap. tlie focussing of the sun's rays on the leaf by drops of water on the cadjan screen. Red Rust The alga which causes the disease known as Red Rust on Tea has also been found to attack the leaves of Hevea, though, as a rule, the resulting damage is inconspicuous. It causes small, circular, purple spots, on which the fructifications of the alga (Cephaleuros) are produced. The latter are minute, erect, red hairs, which are crowded together on the spots and give them a velvety appearance. Sometimes, however, the effect is more noticeable. In the worst case of Red Rust yet observed the whole tree had a generally unhealthy appear- ance, its leaves being curled, and mottled green and yellow, the yellow areas being diffuse and not definite spots. The fructifications of the alga occurred on small spots as already described, but, in addition, the leaves had cracked here and there, and the red hairs were present .in lines along the cracks. Only a single tree was affected in this way, and it is probable that, as in Tea, the severity of the attack was to be 9,ttributed to a previous general unthriftiness of the tree. It is generally held that Red Rust is a serious disease only on weak plants. No other disease could be detected on the tree, and in the following year it did not show any signs of Red Rust. Brooks has recorded the occurrence of Gephakuros on leaves of Hevea in Malaya. Abnormal Leaf-pall The most serious leaf disease which has yet made its appearance in the Rubber plantations of the East is that which is known as Abnormal Leaf-fall. In Ceylon and South India, shortly after the rains of the South-West Monsoon have set in, i.e. about the beginning of July, the trees may, if the rains are continuous, begin to shed their leaves, and this may be continued until August. This effect is caused in each country by a species of Phytophthora, which rapidly spreads through the plantations until the disease assumes epidemic | proportions. As these Phytophthoras attack not only the " leaves, but also the fruits, green branches, and stems, the full LEAF DISEASES 89 account of this leaf-fall has been included in a separate chapter on Phytophthora diseases. Another abnormal leaf-fall has been observed in Ceylon on several occasions, but has never affected any large area. It usually occurs on young foliage, shortly after the leaves are full - grown, and more especially if heavy rains occur during the production of new leaves after wintering. On the young leaves large, irregular, blackish-green, watery-looking patches occur, often along the mid-rib. Older leaves may turn yellow, and then olive or brown. Black spots, often with a grey centre, appear on the veins and mid-rib. The leaf -stalk turns dark brown or black, along part or the whole of its length, and may bear dry grey areas in the middle of the discoloured region. The leaves fall off, sometimes as whole, or the leaflets separate from the leaf-stalk, though all the parts fall at the same time. There is usually a slight covering of white mycelium on the back of the leaf. The fungus in this case is Gloeosporium alhorubrum, and its fructifications appear in the form of minute pinkish-red pustules, particu- larly along the veins and on the leaf-stalk. The disease may spread from the leaves to the green ends of the branches and kill them back. In one instance the leaf-stalks bent at the point attacked, and where the leaves came in contact with the green stem they communicated the disease to the latter. . That case, however, appears to have been an exceptional one. In general, the disease is conveyed to the green part of the branch by spores, or, in some cases, by travelling down the leaf-stalk. Gloeosporium alhorubrum sometimes attacks the fruits, and produces a fruit disease similar to the Phytophthora fruit rot. Its effect differs in that the fruit wall does not become as soft as in the latter disease, and, in the most advanced stage, dries, and becomes greenish-grey and minutely wrinkled. In one attack, on nearly ripe fruits, many of the fruits dehisced normally, though the seed was " light," i.e. the kernel had shrivelled up.' The pustules of the Gloeosporium appear all over the affected fruits, and in some cases are so numerous that they coalesce and cover the wall with a continuous pinkish-red layer of spores. The effect of Gloeosporium on the young leaves closely resembles that of Phytophthora ; and as Gloeosporium albo- 90 THE RUBBER TREE c=^- ruhrum very frequently occurs on leaves and fruits whicli have been previously attacked by Phytophthora, it would appear open to question whether in the disease described above the Gloeosporium is not merely a follower. But as examination has not demonstrated the presence of a Phytophthora in these cases, it is probable that the Gloeosporium is the primary cause. Axens has recorded an abnormal leaf -fall in Java, which he attributed to Gloeosporium. In one case it affected five trees ; in another two trees were attacked, one of which lost all its leaves, while the other, which stood close to it, was only partly defoliated. Both cases occurred at the same time, and in each the trees had just acquired their new foliage after wintering. The appearance of the fallen leaves and leaf- stalks was identical with that described above. Arens decided that the Gloeosporium in these cases was Gloeosporium elasticae. He was unable to produce the leaf -fall by inoculat- ing young leaves with the spores of the fungus. Brooks observed a leaf-fall caused by Gloeosporium albo- rubrum in Malaya, and described the occurrence as foUows : " Where Gloeosporium alhorubrum occurs on recently unfolded Rubber leaves it causes them to shrivel from the margin and fall rapidly from the tree. On a few mature trees growing in low-lying land I have seen this fungus so abundant at the time of unfolding of the leaves after ' wintering ' that the ground below was thickly carpeted with the leaves which had been shed. Leaves of Hevea brasiliensis at the time of imfold- ing are of delicate texture, and are much less resistant to fungoid attack than when fully developed." Another Gloeosporium leaf-faU was found in Ceylon in 1905. It attacked young plants, about a foot high, in the nursery, the leaves turning yellow-green, then yellow, and finally falling off. There was a general discoloration and death of the whole leaf blade, not, as is the more usual in leaf diseases, a formation of isolated diseased patches. The spore pustules of the fungus appeared on either side of the leaf as minute pale-brown masses. The fungus was named Gloeosporium Heveae. A diminution of the shade made the conditions less favourable for the development of the fungus, and the leaves which were subsequently produced were not attacked. LEAF DISEASES 91 Several instances of leaf-fall have been recorded which could not be attributed to Phytophthora or Gloeosporium. In August 1909 an extensive fall of leaf occurred on some estates in Ceylon, In most cases the trees were only partly defoliated, the leaves falling especially from the outer branches and leaving bare shoots all over the outside of the head. In some instances all the leaves were shed, while iu one case, where the trees were exposed to the south-west wind, they became bare on the south-west side only. As a rule the leaves were green when they fell, and they did not show any signs of a fungus attack. This year was an excep- tionally wet one in the districts in which the leaf -fall occurred, and it was concluded that the fall of leaf was attributable to the effect of the heavy rainfall. The rains ceased towards the end of August, and the trees put out new leaf in the following two months. Rutgers, in Java, has recorded a Avidespread occurrence of leaf-faU in which no fungus could be detected, and attributed it to the same cause. Similarly, Dastur states that, in a leaf -fall observed by him in Burma, the falling leaf- stalks were healthy and the leaves did not become curled or flaccid, and he was inclined to attribute it to excessive humidity. A sudden fall of green leaf from a single tree in wet weather may be the result of an attack of root disease. One such case was observed at Peradeniya in 1917 at the beginning of an attack of Fames lignQsus ; and trees which are said to be " always " the first to be attacked by " leaf-faU " are frequently found to be suffering from the attack of a slow- acting root disease, e.g. Fomes lamaoensis. When timber is burnt among Rubber the hot smoke and gases from the fires may cause a fall of leaf from the neigh- bouring trees. Mildew The term " mildew " is usually applied to fungi which form superficial white powdery patches on leaves and green stems. A large number of these fungi is known, all of them strictly parasitic on the plants on which they occur ; some of them are the cause of serious diseases in temperate countries, as, for example, the Hop mildew. Oak mildew. Gooseberry mildew, etc., while in the Eastern Tropics the Citrus mildew 92 THE RUBBER TREE ^hap. often kills back orange trees. Thougli the bulk of the fimgus is external, it gives off branches which penetrate into the host plant, and ultimately kill the leaves and green twigs. A mildew has been found on Hevea in Java, and is said to occur on Rubber throughout that country, but it has not yet been reported from other Rubber-growing countries. It attacks the trees just after " wintering," and the resulting damage depends to a great extent on the stage of develop- ment of the leaves at the time of attack. The very young leaf of Hevea, when first unfolded, is brown and shining. When the leaves are attacked in that stage they become dull and faded, and in some cases the tip and sides of the leaflets curl underneath. A few days later the leaflets fall off, not all at the same time, but in succession. The leaf-stalk remains attached to the twig for some days longer, and then falls. On some of the leaves part of the mid-rib and the lateral veins on the under surface are covered with a fine white coat, while in severe attacks the white covering spreads over part of the adjacent surface of the leaf, and sometimes extends on to the upper side and over the apex of the leaf -stalk. As the leaves in this stage are very small and tender, they quickly dry and shrivel up, and nothing much is noticeable on the ground beneath the affected trees as a rule. But if attention has been drawn to these leaves on the ground the disease can generally be detected by an examination of those still on the tree, or by the condition of the yoimg branches. If the leaves are attacked when they are half-grown and have become green the effect is somewhat different. The leaves become dull and yellowish, the tip of the leaf curls under and sometimes dies off, and the edge of the leaf does not develop normally, but becomes distorted and irregularly notched. As these half -grown leaves are more resistant than the very young leaves, many of the leaflets do not fall off when attacked in this stage. Some leaves lose only one leaflet, some two, out of the normal three. Consequently the twigs bear leaf -stalks from which all the leaflets have dropped, and others which retain one or two of them, and the latter subsequently complete their development normally. As in the case of the younger leaves the fungus occurs on the under surfa.ce ; it is generally more easily discernible than on the LEAF DISEASES 93 former, but sometimes it is scanty even on the half-grown leaves, and can only be detected with the aid of a microscope. When fully-developed leaves are attacked they do not fall and are not distorted. They then bear velvety dis- coloured spots, in this case chiefly on the upper surface, on which fine superficial threads can be detected with a lens ; these subsequently become more conspicuous owing to the formation of conidia which give the spots a white powdery appearance. Similar patches also occur on the tips of the green shoots. The effect on the tree varies according to the severity of the attack and the stage of development attained by the leaves at the time. If the leaves are just shooting and the attack severe, the tree may become almost leafless again in a very short time. If the attack is less severe, or the leaves half-grown, only part of the foliage is shed, and the crown becomes more or less thin. If the whole of the tree has not wintered at the same time, the effect may appear to be con- fined to one side of the tree, or to one branch, that being the only part in young leaf at the time of attack. The occurrence of numerous leaf-stalks which bear only one or two leaflets, and those distorted and crumpled, is a special feature of this disease. The fungus attacks the young blossom especially severely, and the growth on the inflorescence may be so luxuriant that it appears as if covered with flour. The flowers then do not develop and no fruit is formed. As is usual with mfldews in the Tropics, only the Oidium, or conidial, stage has been found. The conidia are barrel- shaped, and occur generally singly at the apex of short stalks. They measure 28-42 x 14-23/^. The disease usually occurs on old Rubber in tapping, but it has been found on two-year-old trees and on seedlings just sprouted. In the latter case the plants died. Species of Oidium, or of mildew fungi in general, are usually confined to a limited range of host plants, often to plants belonging to the same natural order. There can be no doubt that the mildew which now attacks Hevea has spread to that plant from some allied species of flowering plant, and is in process of adaptation to its new host. Mildews have been recorded in the Tropics on Euphorbia Mrta, Euphorha 94 THE RUBBER TREE ™^ Rothiana, PhyUanthics Niruri, Phyllanthus reticulMus, and Jatropha Curcas, all of wMcli are members of the natural order EupJiorbiaceae, to which Hevea belongs. The first three of these are conmion weeds, while the fifth is a very common hedge plant. But attempts to infect Hevea seedlings with the mildews from Euphorbia hirta and Phyllanthus Nvruri in Ceylon have failed. Sooty Moulds The planter is sometimes alarmed by a general blackening of the leaves of the Rubber tree. Frequently only a single . tree exhibits this appearance, but ia some cases a group of two or three trees is affected. As a rule, the blackening occurs on the upper surface of the leaf only, the lower side remaining green, and the leaves do not fall off. On examina- tion it is found that the blackening is due to a thin sheet of fungus tissue overlying the surface of the leaf, and this sheet, at least in the thicker parts, can be peeled off, leaving the surface a normal green. When the leaf is dried the black sheet cracks and scales off. The fungus is not always confined to the leaves, but may extend over the green shoots. The black colour is the actual colour of the fungus, not a discoloration of the plant. Fungi of this type are known as Sooty Moulds. They do not live at the expense of the plant, but on the secretions of scale insects which are present on the leaves. The insects will usually be f oxmd to be present in large mmabers, generally ia the form of small, oval, green, or brown scales, adhering to the leaf, more particularly along the veins. These fungi do not cause any noticeable damage. The way ia which they readily separate from the leaf shows that they are chiefly superficial and do not penetrate into the leaf tissue, though it has been proved that, in some cases, they give off minute projections which pierce the epidermis and help to fix the film to the surface. However, this penetration has little effect on the leaf, as is clear from the fact that the leaf itself is not discoloured and does not fall off. Any small damage which may result from the growth of these fungi is indirect ; the black film cuts off part of the light which would reach the leaf imder normal conditions, and so diminishes in some degree the ability of the leaf to manufacture food. LEAF DISEASES 95 Obviously, since the fungus grows on the secretions of the scale insects, it would be necessary to get rid of the latter if it were thought desirable to remove Sooty Moulds. But the effect of these moulds is quite negligible, and the adoption of any treatment against them is not warranted by the available evidence. Whether it would ever become advisable to adopt measures against the scale insects, on account of the damage done by the latter, is another question. Sooty Moulds tend to be more prevalent during dry- seasons, and to disappear during the rains. This is perhaps due to the efEect of the weather on the insects. Green Hevea shoots and fruits frequently, almost always, bear other fungi of the same class as the Sooty Moulds, but as they form a much thinner film, they are not so conspicuous. These species appear in black cloudy patches, in varying depth of colour, over the green tissue, but not completely hiding it. The patches cannot be peeled ofE, and no fungus threads can be detected except by a microscopic examination ; indeed, they appear to be stains on the green tissue rather than a fungus covering. The tissue underlying these stains is quite normal, and yields latex when cut, and is thereby distinguished from the blackened, soddened wall of fruits attacked by Phytophthora. No scale insects accompany these fungi ; they live on the secretions of the " extra-floral " nectaries which are situated at the base of the Hevea leaf. The patches frequently bear minute, black points, which are the fructifications of the fungus. In Ceylon the species which is found on green Hevea shoots is Chaetopeltopsis tenuissima. Nodules on Leaves (Aschersonia) Another fungus which accompanies scale insects occurs fairly frequently on Hevea leaves and green shoots in Ceylon. It is almost hemispherical in shape, and forms rather hard smooth warts up to five millimetres in diameter, attached to the leaf by a flat base. The colour varies, from pale yellow, or yellow-brown when young, to black when old. Internally it is yellow or orange-yellow (Plate VI., Fig. 10). The fungus does not penetrate into the leaf, and is easily detached from it. 96 THE RUBBER TREE chap. These fungi are not parasitic on the leaf but on the scale insects. Each wart is developed over, and devours, a single scale insect. They are therefore beneficial, and assist the planter by destroying insects which might do damage to the tree. They belong to the genus Hypocrella, but it is usually the lower, or Aschersonia, stage which is found on the leaves of Hevea. Many species of Hypocrella occur in the Tropics, all of them parasitic on scale insects ; the commonest one on Hevea is Hypocrella Reineckiana. SUMMAEY leaf diseases South American Leaf Disease {Fusicladium macrosporum, Kuyper) Identification. — ^Young leaves covered with somewhat translucent, olive-green or blackish-green spots, sometimes so numerous that the whole leaf blackens, withers, and crumples up : spots velvety with minute erect hairs (conidiophores). Older leaves perforated, the holes surrounded with small black points. On the green twigs swellings which become black. Affected leaves fall off. Occurrence. — Attacks leaves of all ages, but is especially destructive to young foliage, three to five days old, before the leaves have fully developed. Trees may be repeatedly defoliated, and die in consequence. Only known to occur in South America, where it attacks both wild and cultivated Hevea. Treatment. — See p. 79. Bird's-eye Spot {Helminthosporium Heveae, Fetch) Identification. — Spots small, circular, not more than five millimetres in diameter, white and semi-transparent, surrounded by a narrow purple-brown line (Plate III., Fig. 4). Occurrence. — Common on nursery plants, about three or four feet high ; rare on old trees. Known in Ceylon since 1905, and reported from South India and Malaya. Treatment. — Has not been considered serious enough to warrant treatment. Shot-hole Leap Disease (? Scolecotrichum Heveae, Vincens) Identification. — Spots at first circular, not exceeding five milli- LEAF DISEASES 97 metres in diameter, more or less translucent, with a violet or brown rim, and a pale outer zone : the centre dries up and falls out. Occurrence. — Found on nursery plants, and on young poorly-grown Hevea, at Para, South America. Gataoavma Huberi (P. Henn.) Theiss. and Syd. Identification. — On the under side of the leaf, a black, shining crust, up to a centimetre in diameter, surrounded by similar smaller patches arranged in a circle. The corresponding area on the upper side of the leaf is pale green. Occurrence. — ^Attacks full-grown leaves, which do not appear to suffer notably, and, if severely attacked, fall only a few days before the normal wintering. Common in the Amazon valley : not recorded in other countries. AscocHYTA EiM Blight {Ascochyta Heveae, Petch) Identifi .^-l»^-'V-' STEM AND ROOT DISEASES VI NON-PARASITIC DISEASES 177 smooth bark, wMcL is uniformly yellowish and granular internally. These trees again yield latex if rested, but it has always been recommended that tapping should be continued, because the renewed bark is of normal quality. The more immediate methods of treatment which have been advised aim at the complete removal of all the affected cortex, so that the formation of nodules is prevented. Three methods have been adopted in different countries, viz. scrap- ing, stripping, and tarring. In the scraping method the diseased cortex is shaved away until latex begins to exude, and is then painted with Brunolinum Plantarium. A piece of sacking should be placed round the base of the tree to receive the scrapings, and the latter should be burnt. The scraping will, in general, leave some areas of diseased tissue on the stem, and these will be killed by the Brunolinum. Further, the penetration of the Brunolinum into the remaining laticiferous layer will partly kill it, and so put out of action the abnormal streaks and points round which the nodules develop ; but the Brunohnum solution should not, of course, be so strong that it kiUs the cortex down to the wood. The strength which may be used without causing wounds must be determined by trial, as estates apparently differ in this respect. Twenty per cent Brunolinum Plantarium should be tried first, and if that causes wounds when applied immediately after scraping, appUcation on the day after scraping should be tried. If the twenty per cent solution does not cause wounds, the strength should be increased. When the cortex dies back after scraping and application of BrunoUnum Plantarium, it does not necessarily follow that the death of the cortex is due to the Brunolinum ; and a few trees should be treated by scraping only, to see whether the cortex dies back when the Brunolinum is not applied. If, in the latter case, the cortex dies back, the patches must not be scraped so deeply. The stripping method of treatment has been largely employed in Sumatra, and is officially recommended in Malaya. In this treatment the whole of the affected cortex is stripped off down to the wood. Thus, not only is all the diseased tissue removed, but also the inner layer, overlying the cambium, in which the nodules develop. The method is N A 178 THE RUBBER TREE chap. no doubt a drastic one, and it would be supposed that it could only result in the formation of a large wound, but experience is unanimous that, when properly carried out, a covering of renewed bark appears over the whole of the exposed wood surface within a fortnight. The procedure is as follows. Ascertain by Hght scraping how far the disease extends, collecting all scrapings ag in the previous method ; and then, with a sharp knife, isolate this area by vertical and horizontal cuts which extend to the cambium, including a margin, about an inch wide, of healthy cortex. Shave this isolated area to half the thickness of the cortex. Carefully lever up the lower edge with a knife, taking care to press on the cambium as little as possible, and then take hold of the free edge and peel off the whole of the shaved cortex. The preliminary shaving is required, as the unshaved cortex is not svifficiently flexible to be stripped off without breaking. Holes appear in the renewed bark wherever the stripped surface has been touched. If exposed to sunlight the bark does not renew over the wood, and if exposed to rain, holes are formed where the raindrops fell on, or the rain-water ran down, the stripped surface. Hence the operator should work under the shelter of a screen, and the treated surface must be protected from sunlight and rain by cadjan or other screens. Screens may be made of any available material, but what- ever screen is used it must not touch the stripped surface. Cadjan screens, or grass screens braced with bamboo, about three feet by two feet, are convenient. Two of these should be leant, overlapping, against the tree, with the lower edge on the ground about a foot away from the trunk, and tied to the stem by a cord at the top. To prevent rain running down the stem over the stripped surface, a piece of cloth, dipped in paraflBn wax, is placed round the junction of the screens with the tree, where the wax should cause it to adhere. It is necessary, for good renewal, to admit Ught, but not direct simlight. For this purpose a third screen is laid against the tree, beneath the other two, and is withdrawn daily for a few hours. White waxcloth aprons protect the stripped surface and admit light, but are expensive. Stripping cannot be done when the tree is wintering, as the cortex wiU not then separate readily from the wood. It VI NON-PARASITIC DISEASES 179 should not be done during droughts, as the exposed area may- then dry up, or during prolonged heavy rains, when the stripped surface may be attacked by fungi. Some cases of injury to the stripped surface by insects or fungi have been reported from Malaya. A mole cricket has been found to nibble the surface, and so cause large wounds. Two unidentified fungi have been found to attack the surface, one of which produces white silvery strands of mycelium which kill the underlying tissues, while the other forms white powdery patches which become black. Mouldy Eot and Black Thread also attack newly-stripped surfaces, and hence this method should not be adopted where these diseases are prevalent. Unfortunately, it has not yet been found possible to treat the stripped surface with any preservative solution without damaging the renewal. Covering the surface with paraffin wax is said to have been successful. The wax is melted, is kept hot by means of a portable fire, and is sprayed on with a garden syringe immediately after stripping. When the cortex renews, the wax falls off, and may be collected and used again. If the direct rays of the sun fall on the wax, it melts, and the sunlight injures the renewing tissue ; hence the use of wax should be discontinued six weeks before the wintering season. Stripping has been carried out successfully on an experi- mental scale in Ceylon, but it has not been generally adopted. In Malaya, after extensive trials, it appears to be falling into disfavour owing to the injuries caused by it. The method would appear to be one which can only be done successfully by skilled labour under the closest supervision. The tarring method was invented by Harmsen in Java, where it is said to have given very good results. The extent of the affected patch is determined, as above, and it is then partly isolated by deep horizontal and vertical channels. These channels should not extend to the wood, as a com- pletely isolated patch may die back. If the affected patch does not extend across the vertical (tapping) channel, the latter may be deepened to form one boundary. The patch is then shaved to half the thickness of the cortex, and is then painted with hot coal tar, heated until it begins to bubble. If the disease extends into the renewing bark, the latter should have the outer brown layer only removed and then tarred. 180 THE RUBBER TREE chap. It is claimed that the application of tot tar promotes the growth of the underlying cortex, and that in some cases the treated bark is re-tappable, i.e. gives a good flow of latex, within three months. In cases where a thick, brown, dead scale has formed, this should be prised ofE. If the stripping method is being used, the imderlying layer may be stripped in the usual way, though the operation wiU require great care. In general, however, it will be found more satisfactory to paint the under- lying layer with 10 per cent BrunoUnum without scraping. In old cases, where nodules have already formed, the nodules should be cut out in the usual manner and the woimds painted with 10 per cent BrunoUnum, or tarred. In such cases woimds wiU inevitably be caused where the nodules have become united to the main wood of the stem. The whole of the area affected by Brown Bast must be treated. This will often involve the treatment of the tap root and the lateral roots. The holes which are dug round the trees should be left open and drained so that water does not lodge against the treated patches. Brown Bast, as a rule, attacks the side which is, or has recently been, in tapping. This is a point against the adop- tion of Change-over systems of tapping. If one side is tapped out completely, the other is not likely to be attacked by Brown Bast in the meantime. But if the first side is left when, say, six inches have been tapped, the remaining bark may be found to be attacked by Brown Bast, when it is desired to return to It. Nodules The development of burrs on the stem of Hevea was first noted in the East in 1904, and it is now of common occurrence in aU rubber-growing countries. The affected stems may bear a single, large, more or less uniform swelling on one side of the tree, extending from the base to a height of two or three feet, or a number of smaller, sub-hemispherical pro- tuberances clustered together in an irregular mass. Fre- quently elevated ridges extend from the edge of the larger swellings over the surroimding area of the stem. In the days of pricker tapping the clustered burrs were the more frequent, NON-PARASITIC DISEASES 181 but at the present time the type generally met with is the single large swelling. Where burrs of several years' growth Fig. 22. — Burrs on a Hevea stem. are present, the whole of the lower part of the stem becomes gnarled and knotted, and tapping is impossible. 182 THE RUBBER TREE chap. These swellings are the result of the formation, in the cortex, of a mass of wood, which is generally known as a nodule. At first this woody mass is small, and its presence is only indicated by a slight elevation of the bark ; in this stage the nodule is embedded in the cortex, not united to the wood of the stem, and can be shelled out quite easily with a penknife. Each nodule possesses a cambiimi of its own, distinct from the main cambium of the stem. Consequently, it increases in size by the addition of layers of wood aU round it ; and as it grows larger it causes the characteristic swellings. In its older stage, or sometimes when the nodule is quite small, it develops points on the inner surface which unite with the main wood of the stem, so that ultimately the wood of the stem and the nodtde are continuous over part of their opposed surfaces. The bark over the nodule, or more especially over the grouped forms, becomes deeply cracked and fissured, and often splits ofE in large scales. Latex sometimes exudes from the cracked cortex and runs down the stem. In many instances the latex from the cortex surrounding or covering the nodule is yellow, varying from a pale yellow to a deep chrome. Sometimes the cortex separates from the stem internally, and latex collects in the cavity, subsequently forming a rubber pad. Rubber pads up to three oimces in weight have been taken from such situations. Nodules in their earliest stages differ very much in shape, and the ultimate form of the burr, or swelling, apparently depends to a great extent on the initial shape of the core or nodule. But practically all of them can be classified imder two types. In the one type the nodules are at first small, spherical, or elongated bodies, one or two millimetres in diameter. These may increase in size until they become large, more or less hemispherical, or cyhndrical masses. If several of these small nodules occur close together their cambium layers may meet and unite, thus producing a multiple nodule, but such a one would generally even up in further growth into the same shape as the foregoing. Often a large nodule in the course of its growth meets and fuses with small nodules, and the latter then appear as excrescences on the surface of the larger. Instances of the fusion of small nodules are shown VI NON-PARASITIC DISEASES 183 on Fig. 23. In this way a sheet of wood may be formed, though it would appear that, as a rule, the sheet nodules belong to the second type. In the second type the nodule at first is a network of wood, or a sheet perforated with small holes, whichever one chooses to regard it. Such a sheet may be only a millimetre thick, yet it may extend up the stem for a length of several feet. At first it is embedded in cortical tissue, the latter Fig. 23. — ^Nodules ; earlj' stages. Natural size. being continuous' from side to side of the nodule through the perforations, but as its cambium adds new layers of wood the holes are closed up, and it becomes a thin continuous sheet, sometimes with depressed lines here and there which mark the sites of previous holes. The most remarkable feature about these plates is the large area they extend over while they are still so thin that they can scarcely be extracted entire. When these plate nodules thicken, the resulting burr may be several feet in length, but comparatively sUghtly elevated. One such nodule, taken from a tree which had 184 THE RUBBER TREE been tapped by a prickmg method, was 4 feet 9 inches long, 6 inches broad, but only 1 inch thick. The surface of a nodule is usually marked with raised ridges, running in par- allel undulating lines, and here and there forming closed curves. A similar pattern sometimes occurs on the stem wood behind the nodule. The formation of one nodule appears to be fol- lowed by the production of others in the surround- ing cortex. It would seem that, once this fomiation has been initi- ated,the stimulus spreads over the stem ia aU directions from the point of origin. Crops of small nodules frequently occur round large nodules, especially when they are grouped in clusters. Nodules have not, how- ever, been observed on the parts of the tree below ground, nor had they been found on exposed lateral roots, even in cases where the stem was badly burred down to the ground level, before the appearance of the nodules following Brown Bast. On cutting across a small nodule, a dark-brown point or line is found in the centre. In the case of thin plate nodules a line extends along the middle of the nodule, almost from side to side, but in small, spherical " pea " nodules only a minute brown point may be evident. This coloured point, or line, is the section of a line, or sheet, of cortical tissue round which the nodule has been built. As was first shown by Bateson, and confirmed by Bryce, this browned tissue consists of one or more latex vessels, surrounded by cells which contain a dark-brown tannin, and outside these a few cortical cells without tannin. Fig. 24.— Nodules, x J. VI NON-PARASITIC DISEASES 185 The formation of nodules, in the most general case, is due to an alteration in the contents of the latex vessels. The walls of the latex tubes become yellow, and the neigh- bouring cortical cells are filled with a brown tannin. This sets up an " irritation " in the surrounding tissues, with the result that a cambium is formed, which buries the abnormal latex vessels in a mass of wood. If only a short length of the latex vessels is concerned, the nodule is at first small and spherical or cylindric, but when the latex vessels are altered over a large area a plate is formed, or the vessels are encrusted in such a way that the nodule assumes the network pattern of the latex vessel cylinder. The altered latex vessels which are enclosed in the nodule belong to one latex vessel cylinder, or row, only. The cause of the alteration in the latex vessels has not been discovered. It has not been found to be associated with the attack of any insect or fungus, and it would appear that a solution of the problem must be deferred until more is loiown about the chemical changes concerned in the formation of latex. Bryce distinguishes four types of nodule, according to the character of the tissue which induced their formation and is embedded in the centre of the woody mass. These are as follows : (1) Nodules formed round altered latex vessels. (2) Nodules formed round lesions in the cortex into which latex has oozed and coagulated. (3) Nodules formed round areas into which latex has oozed and coagulated without any lesion of tissue : in these cases the coagulated latex occupies the intercellular spaces. (4) Nodules formed round areas of cortex from which latex may be entirely absent. Bateson recorded what was at first considered to be another type of nodule from Malaya. These were found on untapped bark on trees about five years old, and were small spherical bodies of the kind to which the name " pea disease " is often given. They did not occur promiscuously over the stem, but were confined to the leaf-scars. The leaf-scars of Hevm are well marked on the twigs, where they form brown, semi-oval, or horseshoe-shaped patches. On the older branches they are larger, but on 186 THE RUBBER TREE chap. rough-barked trees there is usually no trace of them left on the old stem. On smooth-barked trees, however, the leaf- scars persist on the main stem, and are evident for many years as horizontal lines, up to four inches long, with a depression in the centre. On examination of these leaf -scar nodules, a short thread of rubber was found in the centre of each. Bateson accounts for the presence of this by supposing that it is part of the contents of one of the latex vessels which accompanied the vascular bundles from the stem to the leaf. When the leaf falls, the ends of the vascidar bundles, which suppUed the leaf with water, ete., remain embedded in the cortex, and as the stem increases in circumference they are carried sideways and become widely separated. The strands of coagulated latex may then give rise to nodules, as in the case of tapped trees. Nodules were especially common in renewed bark, a few months old, after pricker tapping, whether the tree had been tapped by using the pricker only, or by using the pricker after the cortex had been excised to the customary depth with the knife. It was formerly thought that this might be due to the stone cells which occur in large numbers in renewed bark after pricking, but further examination has shoAvn that these nodules contain latex vessels in the centre. During recent years, nodules have been found to develop in large numbers after attacks of Brown Bast. This fact was originally discovered by Rutgers. The effect does not follow an attack of daret-colouied Canker as a rule. When Hevea cortex is attacked by Brown Bast the greater part of it ultimately forms a thick, dead, brown scale, leaving only a thin laticif erous layer, usually less than two millimetres thick, overlying the cambium. This layer at first sight appears healthy, but, on cutting into it, it is found that it contains minute points or patehes or streaks of discoloured tissue. Nodules subsequently develop round these dis- coloured specks, and Bateson has shown that the nucleus of the nodule, in this case also, contains altered latex vessels. The production of nodules after an attack of Brown Bast is thus due to the presence of altered latex vessels in the remain- ing cortex, and it is consequently to be regarded as a secondary effect of the disease. VI NON-PARASITIC DISEASES 187 To Slim up the matter briefly, nodules develop round abnormal regions in the cortex, most usually round altered latex vessels, A part of the cortex becomes abnormal, and the tree proceeds to put it out of the way by burying it in a mass of wood. Each nodule is a cofl&n. Unfortunately the process of cofl&n building, once begun, is continued indefinitely. Small nodules may, in some cases, work out. Bryce records the finding of nodules of fair size in dead bark scales which were on the point of dropping to the ground, on Hevea trees thirty-five years old. It is not uncommon to find small nodules with their outer surface exposed, and it is probable that these would dry up completely and be shed with the dead bark. Nodules are usually found on tapped trees. Bateson, as noted above, has recorded the formation of pea nodules on untapped trees in Malaya, but, in Ceylon, Bryce states that the common type of nodule, that which develops round altered latex vessels, does not occur on untapped trees, the nodule-Uke structures on the latter being globular shoots. According to Bateson, severe tapping favours the develop- ment of nodules. Tapping certainly appears to induce nodule formation in some trees, while others, equally tapped, remain free from them. There appears to be a probability that some strains of Hevea are less subject to this abnormality than others ; hence freedom from burrs is a character which should be required in the selection of seed bearers. Nodules should always be cut out. If they are discovered while still small, they can be taken out without damaging the cambium of the main stem ; but if they have become united to the main wood of the stem, their removal will cause a large open wound. In any case, however, they should be taken out, if the tree is to be kept, as the burred area is, or wiU become, untappable, and its extension over the whole of the lower part of the stem is only a matter of time. In taking out these large nodules the whole of the wood of the nodule should be removed, down to the main wood of the stem, and the latter smoothed off. The wound should then be tarred. Large nodules, extending to a height of three feet, and over half the circumference of the tree, have been successfully removed from trees up to eight years old. 188 THE RUBBER TREE Globular Shoots Bryce examined a large number of untapped trees in Ceylon, varying in age up to eleven years, without finding any instance of the occurrence of true nodules, i.e. woody masses formed round altered latex vessels. Of 2000 seven-year-old trees examined on one estate, about six per cent bore struc- tures which resembled nodules, but these differed from true nodules in not having latex vessels or tannin cells in the centre. These structures are not formed by the deposition of wood round altered latex vessels, but from dormant buds, and are technically known as globular shoots. It is scarcely possible to distinguish globular shoots from nodules except by a microscopic examination, but a rough method is provided by the fact that on cutting across a small nodule a dark- brown point or line is found in the centre, whereas no such discoloured tissue occurs in a globular shoot. The chief difEerence from the practical standpoint is that globular shoots never grow into large woody masses, about one inch being the maximum diameter noted. In one instance, where young Hevea trees had been pollarded, a strong development of globular shoots occurred just below the cut surface. These appeared as spherical or oval protuberances, with a woody core up to about an inch long, the core being quite unconnected with the main wood of the stem. Subsequently these protuberances developed strong shoots. Globular shoots have also been observed in old leaf-scars, in the callus at the edges of woimds, and at the fork of trees with forked stems. In the old leaf-scars they develop from the dormant or latent buds, and may occur singly, or several may be fused together in a horizontal row along the leaf -scar. It is probable that all " nodules " reported on untapped trees, and all which " sprout," i.e. develop leafy shoots, are really not true nodules, but globular shoots. FASCLA.TION Instances of fasciation of the stem of Hevea are not rare. Most estates, during the first two or three years after planting, are able to show one example at least, and it has been VI NON-PARASITIC DISEASES 189 estimated that one case occurs in about every 10,000 trees. As a rule the trees afiected are from one to two years old. In what is perhaps the commonest case the green shoot gradually expands at the apex and becomes flattened, and the edges of the flattened stem increase in thickness more rapidly than the centre, so that it becomes vertically fluted along the middle line and ultimately divides into two stems. Each half now grows independently, and in the course of its growth it curves over towards the other half, until the two stems cross. After crossing, each stem expands into a thin plate with a variously scalloped margin along the thinner edge, but in many cases it makes several complete turns before finally spreading out. The wing-like expansions are covered with small projecting ridges, usually arranged in transverse lines ; these ridges are the scars of aborted leaves. The thinner pdge of the wing is also covered with aborted leaves, or stipules, crowded together. Frequently normal leaves are borne in large numbers on the stem just below the point where it divides, and also along the more regular, thicker edge of the wing. Consequently, a dense, bushy cluster of leaves is sometimes produced, which hides the fasciated stem com- pletely. Figure 25 shows a specimen in which one side especially has executed numerous turns before finally expanding. The example shown in Fig. 26 is formed by the gradual thinning out of the stem on one side, instead of down the middle, as in the more general case. Such one - sided specimens are not uncommon, but they are not usually developed to such an extent as the one photographed. Fasciation in some instances (other than Hevea) is due to the attacks of insects or fungi, but in the majority of cases nothing definite can be stated except that they are certainly not due to either of those causes. There is no reason to believe that either insects or fungi are resppnsible for fascia- tion in Hevea. The abnormal tops should be cut ofi. If left alone the fasciated part of the stem dies, but before that happens a new shoot generally develops lower down the stem. It has been stated that in Java cases have occm-red in which, after a 190 THE RUBBER TREE chap fasciated stem lias been cut off, tlie new shoots wliich subse- Fio. 25. — A fasciated stem, x J. quently developed have also been fasciated. This has not been observed in Ceylon, but it is possible that it might NON-PARASITIC DISEASES 191 happen if the top were pruned ofE close to the abnormal part. It should be cut off about two feet below. FiQ. 26. — A fasoiated stem. Twisted Seedlings Nursery plants with stems twisted at the base are of frequent occurrence. In the most general case the stem 192 THE RUBBER TREE chap. makes a complete turn, either in a regular curve (see tlie fifth from the left in Fig. 27), or in a combination of curves and abruptly angular bends ; in other cases there are two complete turns, and in a single instance three have been observe'd. The curves are rarely all in the same direction, and the resulting combination is frequently so complicated that analysis fails to afford any adequate explanation. It may be noted that the examples given here had been grown in free soil, and do not owe their origin to the presence of stones in the nursery. As a rule, these twisted plants are discovered when they are about to be planted out in the field ; at that time the coUs are generally fused together, and would ultimately, if the plants had been allowed to grow, have formed a solid mass at the base of the stem. The specimens shown in Fig. 27 were nursery plants eighteen months old. After several chance observations on the production of twisted stems, the following experiment was carried out : (a) 50 seeds were planted horizontally with the flatter side downwards. (6) 50 seeds were planted horizontally with the flatter side uppermost. (c) 50 seeds were planted vertically with the micropyle, i.e. the hole through which the root emerges, downwards. (d) 60 seeds were planted vertically with the micropyle uppermost. (e) 50 seeds were planted horizontally, and on their narrower side. The results of this experiment are illustrated in Fig. 28. No. 1 (from the left) is a typical seedling of lot (a) in which 48 germinated, all normally. No. 2 represents the seedlings of lot (6) of which 49 germinated, all normally. No. 3 is a seedling of lot (c), one of 47, all of which were normal, though the seeds were raised above the soil. Nos. 4 and 5 are typical of the seedlipgs of lot {d), in which 45 seeds germinated ; 27 of the seedlings had a knee bend, as shown in No. 4, and in 9 others this was accentuated into the shape of an N, while the remaining 9 formed complete loops as illustrated in No. 5. No. 6 is a representative seedling of lot (e), of which 39 seeds germinated, all normally. Experiment (d) was repeated with 20 seeds ; 15 of these NON-PARASITIC DISEASES 193 germinated, 11 with, simple knee, or N -shaped bends, and 4 with complete loops. It would appear, therefore, that s 3 60 S planting the seed with the micropylar end uppermost favours the production of twisted seedlings. 194 THE RUBBER TREE ^^ When the seed germinates, the developing root (radicle) pushes off the circiJar cap which closes the micropyle, and emerges as a white stump, about three or four millimetres in diameter, with a truncate flattened end. As it lengthens, the flattened end becomes slightly conical and its margin develops a number of minute points. The conical central point is the developing tap root, while the marginal points are the developing lateral, or secondary, roots. It is a peculiar feature of Hmea that the secondary roots at first grow much more rapidly than the primary, or tap, root, and serve to fix the yoimg plant as the radicle curves downwards. The two seedling leaves (cotyledons) remain within the seed and absorb the food stored up round them. But the stalks of these leaves are lengthened until they project outside the seed for a length of about a centimetre. The young shoot lies between' the two leaf-stalks, its tip being situated just within the seed. After the tap root has developed, the shoot emerges sideways from between the leaf-stalks in a loop. This loop then turns upwards, and, as it elongates^ the tip is pulled out of the seed, and the young shoot straightens out and becomes vertical. When the seed is planted with the micropyle uppermost, the radicle, on emergence, points verticaUy upwards, and subsequently bends over. Consequently, unless the seed is planted deeper than usual, the radicle protrudes above ground before it begins to curve downwards. The secondary roots are then produced in the air, and in the extreme case they may wither before reaching the soil. But in all cases, even when the radicle does not project above the soil, the emergence of the looped shoot is considerably delayed, because that does not occur until the radicle has curved over so that its tip points verticaUy downwards and the secondary roots have been produced. During this delay all the parte outeide the seed, including the two leaf -stalks, become much thicker than in normal germination. This thickening has two results : it makes the curve in the base of the stem so rigid that it cannot subsequently straighten, whQe the two leitf-bases hold the shoot, when it endeavours to pull iteqlf out, as in a vice. These two factors cause all the twiste. If the looped shoot becomes free, the only curve or twist in the stem is that which is caused by the downward curve of NON-PARASITIC DISEASES 195 the radicle, and this takes the form of a knee or an N bend, as in No. 4 of Fig. 28. Nos. 2 and 3 of Fig. 27 are similar bends. But in many cases the loop is held so firmly by the thickened leaf-stalks that it cannot pull out. No. 5, Fig. 28, shows this ; the loop has not straightened out, but the tip of the shoot has emerged from the seed and has curved up- wards on the outside of the seed-leaf stallc, forming a complete loop. Nos. 4 and 7 of Fig. 27 are examples of the same condition. In some instances the tension in the loop of the young shoot when it endeavours to straighten out is so great that it breaks close to the tip. The shoot has then no growing point at the apex. Headless seedlings of this description, with a shoot about eight inches long, but without a terminal bud, are not uncommon. They usually produce shoots from the buds in the axils of the seedling leaves, and thus double- stemmed plants are formed. Cork Warts This phenomenon has, up to the present, only been observed on two occasions, in the one case on the upper part of the main stem of an old tree, and, in the other, on a young tree, about five inches in diameter. The stem bore numerous outgrowths of bark, like small pyramids, usually six-sided and flat-topped. Towards the base of the stem these were crowded together side by side in large patches, covering the whole circumference. Higher up they occurred on smaller isolated patches, while, at a height of about three feet, solitary pyramids emerged through the bark. In some places they were arranged in curved Imes (Fig. 29). The individual pjrramids are usually erect, but sometimes curved. Some attain a height of an inch, though most of them do not exceed three-quarters of an inch in the only available specimen. AU of them, however, project above the surrounding bark. At the base they are up to half an inch broad, and diminish in breadth to about a quarter of an inch at the apex. Several may be united from base to apex at first, and separate later. Their sides are marked with lines 196 THE RUBBER TREE ^^■ paraUel to tlie base, as thougt they were built up of thin layers one above another. The cortex surrounding these outgrowths appears normal. Beneath them it is greatly reduced in thickne"ss, and con- sists of a thin, laticiferous layer, only about one milli- metre thick, just enough to hold the pyramids together. The pyramids are composed entirely of cortical tissues ; very few stone cells are pre- sent in them, and these usually occur as isolated cells, not in groups. No fungus has yet been found to be associated with this formation. Malformed Stems In a few cases, young trees, about three or four inches in diameter, have stems which are covered with rounded pro- tuberances over their whole length. These protuberances resemble the swellings caused by nodules, but on cutting into them it is found that they are not due to the development of woody masses in the cortex, but to swellings on the main wood of the stem. A similar efEect has been observed to follow wounding on small stems, but in this case the swellings bore obvious scars, and on cutting into the wood the blackened surface of the old wound was found buried in the wood at a depth of about half an inch. In the most general case, however, the bark over the swelling is normal, and there is no evidence of previous wounding. Such trees have been styled " knobbed trees " (knobbel-boom) in Java. In a somewhat similar case the protuberances take the Fio. 29. — Cork warts, x J. NON-PARASITIC DISEASES 197 form of elevated rounded ridges running longitudinally up the stem. These ridges unite witli one another here and there, and form a netted pattern with deep depressions in the meshes (Fig. 30). The appearance recalls that of one of the strangling figs [Ficus parasitica) overgrowing a stem. The bark over the ridges does not exhibit any signs of injury, and examination shows that the ridges are due to swellings on the main wood, not to a development of nodules in the cortex. Young trees which have these malformed stems should be removed, as they do not develop into tappable trees. A Twisted Hsvea Stem The photographs on Figs. 31, 32 show the stem of a two -year -old Heoea, two inches in diameter. At a height of six inches from the ground the stem makes three complete turns, and above these it is marked by a spiral groove for a length of nine inches. It wiU be seen from the photographs that this spiral groove begins near the upper edge of the last coU. The specimen had been broken before it came into my pos- session, and the fracture is shown by the line across the middle coil, where some of the bark has been broken ofi in the attempt to fit the two pieces together. The coils are quite free from one another, that is, they are in contact but not fused together. The stem has undoubtedly been coiled completely round three times ; it is not merely grooved. When the stem is broken across the middle turn it is seen to be coiled round a much thinner dead stem. This is evident in the second photograph, which shows the upper part of the stem inverted. From this the explanation of the pheno- FiQ. 30. — ^A ridged stem, x |. 198 THE RUBBER TREE menon is fairly simple. When the young tree was planted out in the field it was, as usual, " stumped." The stem then died back to the next node, and the new leading shoot sprang from the bud at that node. But instead of growing straight up by the side of the dead stem, it coiled round the latter three times. The cause of this coiling is revealed in the 1 .fBI ( ► ■9^^ 1 '"::..:^i 1 \ f f Fig. 31. Fig. 32. A twisted Hevea stem, x J. second photograph, where, stiU twined round the dead original stem, is seen part of some cLLmbing weed. This climber grew up the stem of the young plant, and arrived at the bud just as the latter started into growth ; and in twining further round the dead part of the stem it carried the young shoot round with it. "When the two reached the top of the dead stem the Hevea shoot grew straight upwards, and the VI NON-PARASITIC DISEASES 199 climber then twisted itself round the green shoot ; this is shown by the spiral groove on the upper part of the stem, which is caused by the pressure of the coils of the climber on the young stem as the latter expanded. It is most probable that the coils of the Hevea stem were at first wide apart, but they have come into contact owing to its subsequent thickening. If the tree had been allowed to grow the coils would no doiibt have become fused into a solid mass. Scorched Trees In many cases trees have been scorched by leaf fires, or by burning timber among the standing trees. Such trees are quickly attacked by boring beetles, and usually in a few days the bark is riddled with holes from which sawdust is falling down the stem. Afterwards Ustulina zonata frequently enters the damaged stems and completes the work of destruc- tion begun by the beetles. The scorched area most often extends in a long strip up one side of the tree, sometimes over half the circumference. If the fire has run rapidly through the field the damage may be confined to the renewing bark on the tapping surface. In some cases, when a leaf ficre has progressed very rapidly, the chief damage may be on the opposite side to that first reached by the fire, as the leaves may burn more slowly on the lee- ward side of the tree. The damaged trees should be treated as soon as possible, before they are badly attacked by borers. If they are severely damaged the whole of the scorched cortex should be cut out down to the wood, and the wound painted, first with Brunolinum, or Solignum, etc., and after that is dry, with coal tar. If only the outer parts of the cortex are damaged these should be scraped or cut off until healthy tissue is reached, and the surface then treated with Bruno- linum and tar as above. The affected area should be inspected daily for about a week to make sure that no damaged trees have been missed. It is often diflSlcuIt to determine whether trees have been injured or not, as the damaged bark in some cases is not blackened in any way. Such trees may easily be overlooked, until the borers find them out. From several occurrences 200 THE RUBBER TREE chap. examined in Ceylon it would appear that the borers attack the trees which are lightly scorched more readily than those which are severely scorched. If the bark is charred the beetles may not attack it at all. Various methods have been suggested for the avoidance of leaf fires in countries where there is a definite dry season. Forking in the leaves in lines between the rows of Rubber appears to be one of the most reasonable. Leaf pits would seem, from a mycological point of view, to be open to sus- picion, and they are likely to prove dangerous where Fomes lignosus prevails. Where jungle roots, or felled Hevea, must be burnt among the standing trees, care should be taken to keep the heaps small. It has been suggested that the stems of the sur- rounding trees should be protected by having sheets of galvanised iron placed against them on the side nearest the fire, but obviously this would entail great expense, unless only a few heaps were fired at the same time. On many estates in Ceylon it is possible to find a more or less clear space at the bottom of a ravine, and it is worth while to expend a little more on the transport of the timber to such places rather than to run the risk of damaging the remaining trees. Black Patches in Hevea Wood When Hevea which has been in tapping for some years is thinned out, black patches, extending longitudinally up the stem, are often fotmd in the felled logs. Sometimes the trees are split in the course of felUng, and these patches thereby exposed. These have on several occasions been considered an indication of some new disease, but, though they are not normal, they are quite harmless, and are perhaps an inevitable consequence of tapping. They are sometimes called " burnt patches," which exactly expresses their appearance. These black marks are the result of old tapping wounds, or of wounds caused by disease on the tapping surface or elsewhere, which extended to the cambium but did not set up a pronounced decay of the wood, e.g. wounds caused by Canker or Black Thread. When such wounds are healed the exposed surface is buried by a new growth of wood, but, VI NON-PARASITIC DISEASES 201 o'wing to the development of saprophytic fungi on it when exposed, or its oxidation through exposure, and subsequent changes after burial, the old surface is blackened. Once the wound is healed the blackened area is buried deeper and deeper every year as the stenx increases in thick- ness ; and as the tree is not grown for timber, the hidden defect is of no importance. It can have no efiect on the general health of the tree. When the tree is split, separation occurs most easily along the line of such a patch, because the layers of wood on the two sides of it are not organically united. The trees which were tapped years ago by Vs which extended to the wood now carry the pattern of the old tapping within the stem. Every wound on the tapping surface is duly recorded as a black mark. This is a some- what depressing fact, but relief may be found in the know- ledge that the black marks cannot be detected until the tree is cut down and split up. The Effect of Lightning The splitting of the stem by lightning, one of its most noticeable effects on trees in temperate climates, has not been observed on Hevea. An indirect efEect of lightning has been noted on several occasions in Ceylon. Two or three trees in the neighbour- hood of a large rock suddenly died, the symptoms being similar to those of a root disease. In these cases the lightning struck the rock, and the trees in the immediate vicinity, though apparently uninjured, died in consequence. Similar instances have occurred in Tea. Rutgers has investigated the effect of lightning on Hevea in Sumatra, where injury due to this cause is by no means rare in some districts. He classifies the effects under four heads : (1) Siagle trees, or groups of trees, may be killed. In some instances one tree is killed, while the branches of the trees nearest to it are withered. In other cases one or more trees are killed, and the tops of the neighbouring trees wither, as in Die-back. The bark may be killed in a longi- 202 THE RUBBER TREE tudinal strip, sometimes nmning spirally down the stem, and the dead strip is soon attacked by borers. (2) Trees which, have been struck by Lightning, but not HUed, may bear short vertical wounds on the stem, some- times arranged in a spiral Une. These may be accompanied by a wound at the collar. (3) The exudation of latex from the upper branches is regarded by Rutgers as another form of injury caused by lightning. (4) The fourth type of injury is the scaling ofE of the Fig. 33. — ^A lightning wound, x J. outer layers of the bark on the upper branches, apparently somewhat similarly to that known as " top canker " in Ceylon. Rutgers considers that this is probably due to Kghtning. Where lightning has merely woimded a tree the cause of the wound is revealed by lie peculiar character of the healing process. The margin of the wound, in the most topical case, shows a double callus. The effect of the lightning is not only to split the bark and wood radially for a short distance, but also to split it internally over a small area along the line of an annual ring. New growth of tissue then occurs from the cambium at the edge of the wound, as NON-PARASITIC DISEASES 203 in tlie case of ordinary wounds, and also from the separated surfaces of the wood along the line of the annual ruag. Fig. 34. — ^Cross-seotion of a lightning wound (diagrammatic). Figure 33 shows a short oblique wound, caused by lightmng, in process of healing, and the accompanying diagram (Fig. 34) was drawn from the cross-section of it. The wood is indicated in the diagram by radial lines, and the cortex by the dotted areas. The project- ing edges of the original cortex have died back, and a growth of callus has taken place over the edges of the wound from the original cambium. In addition, there is new growth (indicated by dose lines) on either side of the wound in the split along the last annual ring. The black regions in the latter situation indicate dead tissue. The illustrations described depict a well-defined case. But many instances occur in which the sear is small, and no open wound is evident. In these cases the outer bark is often not cracked, and nothing is observed until it scales off and reveals the healed scar. Such occurrences are fairly common in one dis- trict in Ceylon, especially on two estates on opposite sides of the same valley. The latter case is illustrated in Fig. 35. The stem, Fig. 35. — Lightning scars, x J. 204 THE RUBBER TREE c=ap. wMcli in the specimen photographed was five inches in diameter, is covered with circular or oval scars one or two inches in diameter. These scars occur scattered over the surface of the trees in large nxmibers. A small patch of bark, often longitudinally cracked, scales ofi, displaying the underlying scar, surrounded by normal bark which is usually slightly upturned round the edge. Sometimes exuded latex is present on the outer bark scale. The surface of the scar tissue is blackish, generally radially grooved and some- times depressed in the centre. When the scars are large the stem is usually swollen, so that old examples are raised, as though a nodule had developed ia the underlying cortex. On stripping ofE the cortex over an affected patch, the main wood of the stem is found to be raised in a gradually elevated swelling under each scar. In some instances the surface of the wood is irregular, with projecting ridges and points, alternating with deep grooves and pits, while the inner surface of the cortex is correspondingly furnished with ridges and grooves, which key in with those of the wood. These irregularities are probably due to the interference of the two calluses. EXUBATIONS OF LaTEX Exudations of latex from the upper parts of the stems or sub-erect branches of Hevea are not uncommon. The latex runs down the stem from one or more points, usually fairly close together, and coagulates in long black streaks. The phenomenon is sometimes referred to as " Weeping of the latex." The cause of this has not yet been ascertained. It was at one time regarded as an indication of Die-back, a view which has now been universally discarded ; and it has also been suggested that it is due to the pecking of the stem by birds. Whatever the cause, it does not appear to be followed by any serious injury to the stem. Rutgers states that hghtning is one cause of this exudation. It may be laid down as a general rule that only healthy cortex can yield latex. If the cortex is attacked by fimgi the latex coagulates in the latex tubes, at least in those diseases which have hitherto been investigated. It would yi NON-PARASITIC DISEASES 205 follow, therefore, that an exudation of latex indicates that healthy cortex has been cut or ruptured. Spontaneous exudation of latex has been recorded in Brazil, where it is stated the trees sometimes burst and the latex flows out, forming a large lump of coarse rubber at the woimd ; and similar lumps have been observed in Bolivia. The phenomenon is not confined to Hevea. Spontaneous exudation of latex has been recorded in Manihot.picmhyensis, and it has been observed in Manihot dichotoma in Ceylon after heavy rains. It has also been recorded in Ficus macro- phylla, in which case it was attributed to excessive pressure of the latex : in the latter it was stated that on strong branches the cracks attained a length of forty centimetres and subsequently enlarged to a breadth of five or six centi- metres, but it did not occur on a regularly tapped tree. In addition to this exudation of latex from the upper branches, which does not appear to be related to any disease, streams of latex flow quite commonly from stems attacked by Pink Disease or tlstuUna. There are (at least) two possible explanations of this effect. In the early stages of Pink Disease, and also of Claret-coloured Canker, the disease may affect only the outer half of the cortex, the part next the cambium being as yet unattacked. If this diseased bark is bored by beetles they may draw latex from the inner sound tissue. This especially occurs if the beetles bore into the bark at a time when the latex will not flow ; they then penetrate into the sound cortex without drawing latex at the time, but latex may exude from the hole later. Again, bark attacked by Pink Disease dries up, cracks, and splits away from the wood : these cracks may extend into tihie surrounding healthy tissue, and latex consequently exudes from the latter. When the fungus spreads further it involves lihe cortex from which the latex issued, and, there- fore, the strands of rubber are found on the parts covered by the pink patch. Exudations of latex are not universal in cases of Pink Disease, but appear to be the more frequent in the cobweb stage. Latex sometimes issues from renewing bark which has been treated with Brunolinum, Tar and Liquid Fuel, etc. In some instances the issue occurs at the edges of small tapping wounds, but in other cases the latex flows from 206 THE RUBBER TREE chap. uninjured bark without any visible crack. Estates vary- considerably in tMs respect, and the mixture which is used with impunity on one may cause bleeding on the next. But though the appearance is unsightly, the efEect on the tree appears to be neghgible. Rubber Pads This name is applied to lumps of rubber found between the wood and the cortex. They are usually circular and plano-convex, being flat on the side in contact with the wood and convex on the other. The bark over the pad may crack longitudinally and some latex may exude and run down the stem. Sometimes the overlying cortex decays, but it frequently remains healthy, especially when it has cracked, and forms two raised hps, or flaps, over the pad. No single cause can be assigned for these formations. It is probable that several agencies may induce this result, but a satisfactory explanation of the most general case has not yet been formulated, for it would appear that as a rule the overlying cortex is not diseased. It would, however, seem that one essential condition for their formation is that the cortex must separate from the wood before the pad is formed. The latex collects between the wood and the cortex, and it would appear obvious that it cannot collect there before there is a cavity between them. Pads sometimes form beneath bark which has been killed by Claret-coloured Canker. If the dead bark separates from the wood, latex may collect behind it, presumably owing to the extension of the separation along the cambium into the surrounding healthy tissue, but this is not of universal occurrence in the case of this disease. According to the accounts of Black Thread in Burma and Malaya, rubber pads are frequently formed beneath the decayed bark in cases of that disease, but they are not common under similar conditions in Ceylon. South states that it has been proved by inoculations that the Phytophihora of Black Thread disease can produce bUsters on the untapped bark at a height of about four or five feet up the stem, the bark subsequently breaking up and disclosing a rubber pad underneath. Quite an epidemic of rubber pads occurred in Ceylon NON-PARASITIC DISEASES 207 during the time the Northway tapping system with, a rotating pricker was under trial. In iJhe system in question the bark at the base of the stem was scraped up to a height of eighteen inches, and the pricker was run round the stem in horizontal lines, the latex being collected in a channel at the base. To assist the flow of latex the scraped part of the stem was syringed with water. In many instances blisters with rubber pads beneath them were formed, and these were cited as damage caused by the pricker, but it was clear that, in general, they were in existence before the pricker was applied, as they bore the marks of the pricker on the outer surface and often contained fragments of bark which had been pushed into them by the instrument. In some cases these blisters were the result of Claret-coloxired Canker, but in others, though the bark died, no disease was traceable. All that could be said was that they followed the scraping and syringing. An interesting case which probably has some bearing on the foregoing occurrence was noted during an attempt to infect Heoea stems with a possible parasitic fimgus. A small patch on the stem was shaved flat, the fungus from a pure culture placed on damp cotton-wool, and this applied to the shaved patch and covered with a watch glass. As the weather turned dry, the cotton- wool pads were moistened daily. The" inoculations were unsuccessful, but in several caseSj both in the inoculations and the controls, a blister with a rubber pad behind it was formed, while the overlying cortex split longitudinally and latex ran down the stem. Thus the blisters and rubber pads were caused by keeping a small shaved patch of the stem continually moist. CHAPTER VII prepared rubber Coloured Spots Before the introduction of the present practice of smoking rubber, the appearance of spots or discolorations on biscuits, crepe, or sheet was a comrnon occurrence. These still occur where the older methods of preparation are employed, but where the rubber is smoked, or thin crepe is made and dried by artificial heat, they are practically unknown. The spots developed when the rubber was drying, and it is no doubt owing to the more rapid methods of drying that the present immunity is due. These discolorations appeared and disappeared in a most mysterious fashion. They might afiect the whole product of a factory for a month and then cease to appear ; or almost all the factories in a district might be producing discoloured rubber for the same limited period. As a general rule, smoked sheet or smoked crepe does not develop spots, nor do they often occur on crepe dried artifi- cially. On biscuits or unsmoked sheet, red, blue, and black spots have been recorded. On thin crepe the spots may be red, yellow, blue, green, or black. Thick crepe is more susceptible to spotting than thin crepe ; but the pigment develops to a greater extent in thin crepe which is converted into thick crepe while still wet than on original thick crepe which has not first been rolled thin. According to Eaton, Grantham, and Day, the difierence is due to the porosity of the rubber, the original thick crepe, made by minimum machining, being more porous, and, therefore, drying quicker than the blanket crepe made from thin wet crepe. The greater the amount of machining in the case of thick crepe, the greater the possibility 208 cHAP.vn PREPARED RUBBER 209 of spotting. These experimenters found that no pigment developed in blocked wet crepe if the pressure employed were sufficient to produce a soUd block, and they attribute that to the exclusion of air. In nearly all the cases investigated these spots have been shown to be caused by fungi or bacteria. These organisms, or their spores, are present iu the freshly-coagulated rubber, and they grow iu it duriag the time it is drying. When the rubber is dry their growth ceases. The latex may be infected iu the field by wind-borne spores, or by the water used when it was customary to water the cuts in the belief that the flow of latex was assisted thereby. Latex diluted previous to CQagulation shows a greater tendency to produce spotted rubber than undiluted latex, and the current belief that rubber is more prone to spotting in the rainy season has been attributed to the dilution of the latex by rain-water, and the consequent introduction of spores. In general, it is held that the latex is infected before coagulation. Whether spots can arise by the infection of the rubber after coagulation has been much disputed. There does not appear to be any reason why infection should not occur during the creping process, from the water used, as the spores might then be embedded in the rubber, just as much as if they had been in the latex prior to coagulation. The point at issue, however, is whether spores which alight on the rubber during drying are able to produce these discolorations. Experi- mental infections of coagulated rubber by sprajdng spores over the surface, carried out by Sharpies, failed when the rubber was hung up to dry, but were successfiil when it was rolled up ; and this has been found to be the case in Ceylon. Arens irSected freshly coagulated Ceara rubber with Bacterium prodigiosum, but how the rubber was kept is not recorded. It appears that, for surface infections to have any result, the coagulated rubber must be kept moist for a cornparatively long time, and under the normal conditions of a properly- conducted drying house discolorations due to such infections should not occxir. Several investigations into the causes of these spots have been made, the most complete being those by Bancroft and Sharpies in the Federated Malay States. There are consider- able differences between the accounts of the various investi- 210 THE RUBBER TREE ohap. gators who have studied the problem, more especially as regards the particular species of fungus concerned in each case, but as a large number of ckromogenic organisms is known, and very many of these may be introduced into latex with infected water, such differences are only to be expected. At the present time the subject is not one of pressing import- ance, for the reasons already stated, and the attention of mycologists has been directed to more urgent problems. Sharpies distinguishes two types of discoloration, viz. spots, where the discoloured area is usually small, and " flushings," where there is a broad, diffused patch of colour. His classification is followed below. Red Spots These usually occur on biscuits or sheet, but have been recorded on bark crepe and scrap. They vary in size up to half an inch in diameter, and are usually circular. The colour is a clear red and extends, as a rule, through the rubber : it gradually fades if the rubber is kept, but does not disappear altogether. Brooks in 1911 recorded that these spots were caused by Bacterium prodigiosum, and that has since been confirmed by several investigators. This bacterium is of world-wide dis- tribution and is the one which sometimes causes red spots in bread. Bancroft obtained from similar spots a fungus which he recorded as probably identical with Monascus heterosporus (Schroet.), and reproduced the spots by spraying freshly- coagulated biscuits with the spores. Black Spots These have been recorded on sheet and crepe. According to Sharpies the black spot is probably the commonest met with on the latter. The spots contain a mycelium which consists of chains of small rounded cells. In culture it forms a black layer of yeast -like cells with a sparse greyish mycelium. Sharpies states that the cells are hyaline, and that the black effect is due to the reflection and refraction of PREPARED RUBBER 211 the Kght in tie large masses of cells. He named the fmigus Chrotnosporium crustaceum. Bancroft investigated a " dark green or almost black " spotting on crepe, and found a fungus which he described under the name of Spottdylocladiuni maculans. He also obtaiiied the same fungus from a '' yeUowish-red colour," and thought that the two colours were produced at different ages of the same mycelium. No infection experiments were carried out. Sharpies considers that the fungus found by Bancroft was not the cause of the discoloration, and that the black spotting examined was probably the blue-black spot on crepe noted below. Black spots have been observed on rubber biscuits in Ceylon. They appeared on the white wet biscuits a day or two after coagulation. The spots were circular, and varied in size from minute points up to patches an inch in diameter. The discoloration extended right through the biscuit, and, when it was dry. numerous dense black points were visible in each patch, in addition to the general black tint. These patches contained numbers of bacteria, together with minute particles of a black pigment to which the discoloration was due. Blue-black Spot on Crepe This spotting has been investigated by Sharpies. The spots are a dense blue-black in the centre, fading out at the edge to a faint \nolet coloration. Successful infections were obtained with a green mould-bke fungus, isolated from the spots, which was identified as Trichoderma Konvngi, Oudem. Sharpies states that this is a very common spot, and was always the first to develop in his laboratory on crepe rubber dried slowly. Dark Blub Spots A dark blue spotting observed by Bancroft on crepe rubber was found to contain stout, dark brown hyphae, con- sisting of short cells. The fungus in culture proved to be Botryodiplodia Theohromae, and Bancroft considered that the crepe was infected from poles of uncured jimgle wood which 212 THE RUBBER TREE chap. had been employed in the diying houses for hanging up the rubber. He found that the spots often occurred on the crepe in transverse bands recurring at intervals, and explained this distribution by supposing that the fungus, both in this case and that of Spondylocladium, had infected the rubber where it was in contact with the poles, the occurrence of the bands at intervals being due to the shifting of the rubber as drying advanced, and the consequent contact along a fresh surface. He obtained both the fungi mentioned from the surface of the poles in question. Bancroft's findings have been criticised by Sharpies, who was unable to obtain a discoloration by infecting latex with pure cultures of Botryodiphdia Theobromae. Sharpies explains the occurrence of the spots in bands by the fact that the rubber in contact with the wood dries more slowly than the rest, and so gives the spores in the rubber a better chance to develop. The Botryodiphdia obtained by Bancroft in pure culture may have been derived from spores on the surface of the rubber, not from the mycehum in it. The spot would appear to be the same as the blue-black spot recorded by Sharpies. Transparent Spots Clear transparent spots sometimes appear on unsmoked sheet or biscuit, a few days after coagulation, whUe the remainder of the sheet is still opaque white. These have been observed in Malaya and Ceylon. In the latter country they are generally circular, and sometimes up to two inches in diameter. The surface of the spot becomes covered with a deUcate white growth, which consists of the conidiophores of the fungus in the spot. In Malaya it has been found that these fungi are of several kinds, usually species of Penidllium and Aspergillus. Opaque Spots According to Sharpies, circular, white, opaque spots are very common on sheet rubber coagulated with acetic acid. Examination of the spots shows that they are due to the presence of fimgus hyphae. Sharpies considers that there is some relation between these spots and the cpmmon green mould, Eurotium candidum, Speg., which always appears on ^^I PREPARED RUBBER 213 the surface of badly-dried sheet rubber, or on any rubber which is allowed to become damp after having been dried. But no success was obtained with inoculation experiments. Broad, Yellow, Diffused Flush This coloration was found on sheet rubber l\y Sharpies, who states that it is seen especially well in sheet rubber coagulated with Bush's powder. This is caused by a fungus which has been named PeniciUium tnaculans. When latex has been intentionally infected with the spores of the fungus, a bright yellow colour is developed in broad patches over the coagulated rubber three days after inoculation. As the sheet dries, the yeUow colour fades away slightly, but it is still quite obvious even when the rubber is dry. The same fungus can give rise to an orange spot in crepe rubber. Violet Flush This occurs on sheet rubber, and has been investigated by Sharpies. It is caused by a fungus, a Fusarium, the violet colour being due to a layer of spores. Red Flush This was observed on sheet rubber in Malaya by Bancroft. The discoloration extended through the sheet. A fungus, a species of Mycogom, was obtained from the discoloured areas. Prevention of Spots The chief factor in the prevention of spots or flushes is rapid drying. Unsmoked sheet and thick crepe are always liable to develop them, but it should be possible to avoid them without much difficulty in the preparation of thin crepe. To assist in the prevention of these undesirable pheno- mena, the addition of formalin, or sodium bisulphite, to the latex before coagulation is recommended, though, according to Sharpies, neither is sufficient to eradicate spots completely under practical conditions, and spots will develop if only the rubber dries slowly enough. Sodium bisulphite has been largely used. It was intro- 214 THE RUBBER TREE chap. duced as a means of manufacturing tliin pale crepe, and a decrease in the amount of spotted rubber coincided with its introduction. This was probably due, in part, to the fact that the crepe, being thin, dried more quickly, rather than to any disinfecting action of the bisulphite. If too much bisulphite is added the rubber tends to dry more slowly, and the fungi have more opportunity of developing. Sharpies gives the amount of sodium bisulphite which diminished spotting in his experiments as one ounce dissolved in one pint of water to each ten gallons of latex, added with constant stirring ; that is, one part of sodium bisulphite to 1600 parts of latex. The amount necessary to prevent darkening of the rubber was given by Clayton Beadle, Stevens, and Morgan as varpng from one part sodium bisulphite to 400 parts of latex to one part to 2400 parts of latex ; the former is the maximum amount, and it is seldom necessary to use so much. The quantity of formalin recommended for the preven- tion of spotting is one part formahn to 800 parts of latex, or 1 pint of formalin to 100 gallons of latex. The use of acetic acid, or other coagulants, in excess of the amount necessary for coagulation increases the liabihty to spotting. As surface infection after coagulation does not produce spots under ordinary conditions it is unnecessary to remove spotted rubber from the drying house, unless it is over- crowded and drying is thereby retarded. Rubber prepared from diluted latex is more liable to becoine spotted than rubber prepared from undiluted latex, but spots are not Ukely to develop on smoked sheet. The use of chinosol has been recommended in Java as a preventive of spots in crepe. Pure chinosol is dear, and commercial chinosol, or potassium oxychinohne sulphate, is said to be cheaper in proportion to its disinfecting power. It is used in 1 per cent solution — one part of the solution to 100 parts of latex. This is an expensive method, and it is admitted that with good drying it is unnecessary. Spotting of Dry Rubber It is sometimes found that rubber which was quite clean and dry when packed on the estate has arrived at the market PREPARED RUBBER 215 centres iu a spotted condition. Eaton has sliown that perfectly dry, clean crepe, if immersed in water for about five numites, sliaken to remove as much moisture as possible, and then rolled up into a cylinder, will develop orange, blue, and yellow spots. The possibility of the development of spots in transit is thereby establislied, provided the rubber is allowed to become damp. The Effect of Spotting on the Rubber It has been generally believed that the growth of fungi and bacteria on raw rubber cannot have any influence on the quality of the rubber because no organism was known which cotild attack, itnd derive novirishment from, rubber itself. Those found in th.e crude rubber could only live on the sugars and proteids in the rubber. Sohngen aui Fol cut out tlie colovired spots from a piece of crepe and com- pared the rubber -with the uncoloured part. They found no difference in the analjrses of the two, and the viscosity curves of the two portions were identical. Hence they concluded that the spots made no difference to the actual value of the rubber. It is to be noted that they did not carry out vulcanisation experiments. Eaton, however, states that rolled-up, wet, thin crepe, in whicli spotting is alwaj'^ very pronounced, does not vulcanise as rapidly as rolled-up sheet, while, on the other hand, blocked, wet, thin crepe, in which spotting does not develop, has its rate of cure accelerated to a considerable extent. Experiments were made by rolling up wet " slab " crepe, i.e. slab which had been allowed to mature for six days, then converted into thin crepe, and immediately rolled up into a cylinder. In this case a marked development of spotting occurred, and the vulcanisation of the rubber was considerably retarded. Eaton states : "It is obvious that these chromogenic organisms utilise, destroy, or change the vulcanisation accelerator formed by the degradation of the proteia by other organisms, so tJiat it no longer behaves as an accelerator. The fact iiiat these chromogenic organisms do not appreciably alter tbe \-ulcanising properties of ordinary slow-cm-ing crepe can be explained on the ground that such 216 THE RUBBER TREE chap. crepe contains little or none of these accelerating substances, and the organisms utilise the protein itself, which already exists in more than sufficient quantity in crepe for normal vulcanisation. Whether the protein in ordinary thin crepe is actually decreased by these organisms has not yet been ascertained." The belief that fungi cannot attack rubber has been challenged by Sohngen and Fol. These experimenters pre- pared thin sheets of rubber, as free as possible from proteids, and succeeded in reducing the quantity of nitrogenous com- pounds to about 0-1 per cent. The sheets were then placed in glass dishes and moistened with a solution containing inorganic salts only, so that the only source of carbon in the medium was the rubber. The dishes were then infected with ordinary garden soil, with the result that two fungi developed on the rubber film. It was found that the rubber became friable and could easily be broken up, and holes occurred in the film at the spot where the fungi had grown. The two fungi were named Actinomyces fuscus and Actino- myces elastica. The authors consider that their experiments prove the existence of fungi which can attack and feed on caoutchouc, but there are several possibilities of error in the methods employed. KusT The term " Rust " is applied to a thin brown film which forms on the surface of smoked sheet as it dries. It carmot be detected until the sheet is scratched or stretched, when the surface film breaks and gives the sheet a somewhat powdery appearance. Eaton, Grantham, and Day state that this is due to a thin film of dried serum, chiefly protein material. The sheet when hung to dry contracts, the serum in it being expelled and ultimately drying on the surface. Anaong the factors which may contribute to this defect they place (a) concentration of the latex, which results in the exudation of a concentrated serum, (6) allowing freshly-rolled sheet to remain in heaps, and (c) placing freshly-rolled sheet where other wet rubber has drained, so that it comes in contact with the old drainings. To obviate rustiness they recom- PREPARED RUBBER 217 mend (a) hanging the sheets to drain immediately after rolling, [b) raeSdag ribbed sheet instead of diamond sheet, and (c) washing the sheet after it has drained for an hour or so, and scrubbing, if necessary, before placing it in the smoke house. The latter method is the one most generally employed ; on some estates the sheet is soaked overnight. The subject has also been investigated by Hellendoorn, who has arrived at somewhat different conclusions. He claims that the deposition of a film of serum substances on the sheet causes "' greasiness," but that " rust " is formed by the decomposition of this film by a micro-organism. This micro-organism flourishes only in the presence of air ; hence rustiness usually appears on the surface which was uppermost in the coagulating pan. But if the sheets are hung too close together rust may form on the side which is then lowest, irrespective of its former position in the coagulating pan, owing to the development of a local damp atmosphere between lie halves of the sheet. Rustiness is favoured by wet weather, and it can be developed at will by keeping freshly-rolled sheets in a damp atmosphere for twenty-four to forty-eight hours before smoking. It may be increased by lengthening the time between coagulating and rolling into sheet. Hellendoorn shows that rustiness does not develop if the freshly-rolled sheet is disinfected by hanging it in formalin vapour ; this is opposed to the theory that it is due to the " sweating out " of serum substances. Disinfection may also be efiected by chinosol or bisulphite, or by immersion in hot water. The latter method is not recommended, because the rubber is injured by that treatment, while ths other methods are not as efficient as rapid surface drying. If the air in the smoke house is sufficiently damp to favour the growth of the micro-organism which causes rustiness, the smoke does not entirely prevent its development. Rustiness, according to Hellendoorn, is due to an infec- tion, and the growth of the organism concerned is depend- ent upon the amount of moisture present. To prevent it, the sheets, inamediately after rolling and washing, should be hung up, wide apart, in a well- ventilated place, or exposed to the wind, and after a few hours should be taken into the smoke house. Leaving the sheets to drip for a night should 218 THE RUBBER TREE be avoided. Rustiness may also be prevented by disinfect- ing the sheets, but as that is not so efl&cient that rapid drying of the surface can be neglected it is not to be recommended. Hellendoorn states that soaking the sheets in water after roUing does not prevent rustiness, and may even increase it ; that sheets from diluted latex develop rustiness more than sheets from undiluted latex ; and that ribbed sheet has no advantage over diamond sheet in this respect. Coloured Latex and Scrap At certain times the scrap on the tree rapidly turns black on the surface. This is said to be more common in some countries when the trees are wintering. On some estates it is found to be worst in closely-planted fields. This effect is not due to a fungus, but to chemical changes which have not yet been completely investigated. It has been stated that, in some instances, rapid discoloration of the scrap is associated with insufi&ciently deep tapping, especially 3 it occurs at the upper end of the cut, while in other cases it is characteristic of individual trees. A pink discoloration of the scrap is also known, but has not yet been explained. In this connection it is of interest to note that Eaton, Grantham, and Day record that slab rubber soaked in tannic acid turned pink. Yellow latex is sometimes a sign of Brown Bast, but not invariably. Tacky Rubber Tacky rubber arises from the exposure of dry rubber to direct sunUght, or heat, or from the presence of copper or iron in the rubber. The copper may be present in the form of copper salts produced by the action of acids on any copper vessel used, or in particles of brass derived from the machinery. Particles of brass may cause green streaks which subsequently become tacky. It is now generally agreed that there is no evidence that tackiness can be caused by fungi or bacteria, or that it can be communicated from one piece of rubber to another: and, though the subject is one which is open to further PREPARED RUBBER 219 investigation, it appears certain that tackiness is due to oxidation. The evidence for and against previous theories, so far as there was any evidence, was summarised in the previous edition of this book, and, as it was based chiefly on specula- tions, it is unnecessary to repeat it. Since that pubhcation, two series of experiments, which appear to be conclusive, have been carried out. In one of these, Eaton added copper sulphate to latex before coagulation, and showed that the rubber, when it subsequently became tacky, increased in weight : this increase is presumably due to the absorption of oxygen in the process of conversion of the rubber into resins. Another series of experiments was carried out by Fickendey. Samples of rubber were exposed to the action of sunhght for eight weeks in sealed tubes containing different gases. Those in hydrogen, nitrogen, and carbon dioxide remaiued unchanged, but those in air and oxygen became tacky. The weight of the rubber in the last two cases had increased, and oxygen had been absorbed. Rubber kept under water remained sound, but rubber immersed in hydrogen peroxide became tacky, though the change occurred only in sunlight. According to Fickendey, moisture decreases the habiUty to tackiness by partially preventing the access of oxygen, while copper and iron salts accelerate the action. Rubber becomes tacky if washed with, or immersed in, permanganate of potash ; this is further evidence in support of the oxidation theory. Moulds on Rubber If kept for any length of time in a tropical climate, prepared rubber is likely to become mouldy. This is especi- ally the case with biscuit and unsmoked sheet. Smoked sheet sometimes becomes mouldy, but crepe rubber is usually free from moulds. The moulds in question are such as develop commonly in the Tropics on leather goods, damp paper, and miscellaneous vegetable substances such as bread, damp tea, copra, etc. They may be yellow or black {Sterigmatocystis) or green 220 THE RUBBER TREE chap. (PenicilUum and. Aspergillus). Sheet rubber left lying in the laboratory for a long time develops patches of any or all of these. An extensive series of observations made on the rubbers from various countries which were exhibited at the Ceylon Rubber Exhibition of 1906 showed that practically all of them became mouldy when left exposed for four months, with the exception of the " wild " rubbers. The freshly- cut surface of a Hard Para ball became green with mould ; this is probably due to the amount of moisture contained in Hard Para, and it illustrates the fact that smoked rubber will soon become mouldy if imperfectly dried ; an examina- tion of any Hard Para ball will usually show that it has been mouldy at some time or other. Crepe rubber, as a rule, did not become mouldy, although it was kept in the same case with other rubbers which did. The difference between crepe and sheet in this respect depends on the fact that the former is more thoroughly washed and dried. The drier the rubber the less possibHity there is of its becoming mouldy. Moreover, these surface moulds live on the impurities in the rubber, and the washing and machin- ing undergone by crepe rubber may remove these to a great extent. It is stated that sheet, prepared from dilute latex and well roUed, is not so liable to moulds as sheet prepared from a richer latex, or sheet not sufl&ciently rolled to express the contained moisture. If dry sheet rubber is stacked, it will, if left long enough in a tropical climate, develop moulds on the exposed surfaces or edges. If, however, damp sheet is stacked, moiild wiU develop between the sheets. Estate complaints of the occurrence of mould generally relate to its development between the time of preparation and packing, or between the time of packing and its arrival at the market centre. In such cases the most general reason is that the rubber was insufficiently dried. To aivoid moulds rubber should be dried as thoroughly and rapidly as possible. Various methods have been proposed for cleaning mouldy rubber and preventing the further development of moulds, but none of them has been attended with much success. Brushing the sheets with five per cent solution of formalin, or with a one per cent solution of chinosol, is recommended in PREPARED RUBBER 221 Java. In that case the rubber should be well dried before being packed. A similar use of creosote has been found unsuccessful. Potassium permanganate should not be used for dis- infecting rubber. If used in any strength in which it is efficacious as a disinfectant, it will turn the rubber tacky, and in the strength usually recommended it is of no value what- ever. The method which appears to be as good as any of dealing with mouldy rubber is to rub off the mould with a dry cloth and to pack it as dry as possible. Whether moulds again develop is in aU cases a matter of luck ; but rubber which has once been mouldy has lost some of the substances on which the moulds feed, and is in some degree less liable to develop moulds again if kept dry. It may be noted that there is no evidence that the develop- ment of surface moulds affects the quality of the rubber. The Effect of Bordeaux Mixture on Rubber It is well established that the presence of copper salts, such as copper sulphate, or of particles of metallic copper, in prepared rubber induces tackiness. If rubber is washed with a solution of copper sulphate it becomes tacky, while if copper sulphate is added to the latex before coagulation, the resulting rubber changes into a resinous sticky mass when dry. Hence it is generally held that Bordeaux Mixture, which is the most efficacious fungicidal spray available for general use, cannot be employed in diseases of Hevea, because it is a copper compound, and if traces of it get into the latex the rubber will become tacky. The experiments which have been carried out to test this point have, however, not been attended by any such result. At Peradeniya a row of twenty-five trees, tapped on alternate days, was well sprayed with Bordeaux Mixture. The trees were tapped with two cuts a foot apart on one-third the circum- ference, and the mixture was applied to the tapping surface to a height of three feet in such quantity that it ran along the cuts and down the vertical channel. Heavy rain fell five days after the spraying, and the rubber of that day's tapping, when analysed, showed 0-00016 per cent of copper in the 222 THE RUBBER TREE ohap. vn biscuit, and 0-003 per cent in the scrap. For six montiis from the date of sprajdng, the rubber, which was all prepared in biscuit form, was kept imder observation, but no case of tackiness was observed. The experiment has been repeated with similar results in Java and Malaya. The question of the employment of Bordeaux Mixture for diseases of rubber trees consequently remains open to further investigation. It is possible that the conflicting results obtained in the experiments quoted depend upon the state of the copper in Bordeaux Mixture, as opposed to that in copper sulphate. Before the adoption of Bordeaux Mixture can be recommended, research is required not only into its action on raw rubber, but also into the behaviour of the rubber during vulcanisation and manufacture. CHAPTER VIII PESTS Mammals All the commoil herbivorous mammals show a partiality for Hevea brasiliensis. Horses and cattle devour the foliage greedily, while goats, wild pigs, deer, and antelopes will strip off the bark from young trees. Hence a liberal use of barbed- wire fencing is generally necessary. Elephants have done considerable damage in Malaya. They not only break off, or uproot, small trees, but, by the destruction of the fencing, open a way for deer and other animals. They are said to eat the roots of the rubber tree, particularly the tap root. Land which has been cleared and planted, and then allowed to lapse into weeds, is particularly liable to be invaded by elephants ; and they are also apt to frequent areas, now under Rubber, which were formerly then- feeding grounds. As elephant-catching is not an estabhshed business in Malaya, that obvious method of reducing their numbers has not been employed. J\Ir. B. H. F. Barnard has recorded a successful method of keeping elephants away from Rubber plantations in Malaya .by a system of patrols. The number and size of the herds in the district, the seasons at which they visited feeding grounds in the vicinity of the plantations, and their usual routes of travel were ascertained as far as possible, and tracks were cut through the forest to enable the patrols to get about the country and keep in touch with the movements of the elephajits. The patrols were unarmed, but were supplied mth. Chinese crackers and bombs, and with these any herd which appeared Hkely to enter an estate was driven back. Porcupines have been one of the most serious pests of 223 224 THE RUBBER TREE chap. young Rubber in Ceylon, and it has generally been customary to pay a fixed sum per head for all porcupines brought in, no matter where they were caught. The porcupine strips the bark ofi the stem from ground level to a height sometimes of two feet, and it may completely ring trees three or four years old. Various patent mixtures have been applied to the stems with the object of keeping ofi these destructive animals, but in no case have they proved successful, though it has been stated that a slight smear of Stockholm tar, not sufficient to penetrate the bark, wUl efiect the desired result. But, in general, it has been found best to rely on the native trapper. The bandicoot usually burrows along undergroimd and attacks the roots or stems of plants below the surface, the first indication of the damage being the falling over of the plant. In the case of Rubber it has been found to attack young trees about an inch and a half in diameter by digging a hole at one side of the plant, and gnawing away the root as far as it can get. It has been suggested that the bandicoot feUs the tree in order to get at the tender bark on the upper parts, but it is the bandicoot's habit to feed on roots, and, in general, it pays no attention to the fallen plant. As this animal usually feeds underground, it is impossible to protect the plants by the application of any mixture, and the native trapper must again be relied on. Small rodents have been recorded to have been responsible for the destruction of a considerable acreage of young Rubber in Malaya shortly after planting with basket plants. The attacks were always in areas which afiorded plenty of cover, e.g. roots, stumps, and unburnt timber, and the animals did not appear to go far into the open. Planting put strong stumps, or clearing the affected area of timber, etc., is recom- mended in such cases. Insects A large number of insects has been recorded as found on Hevea plants, but the only serious pests observed up to the present time are the AVhite Ant (Termes gestroi), the Rubber Leaf Mite, the Root Borer {Batocera ruhus), and, in Java, the Locust {Cyrtacanthacris nigricornis). viii PESTS 225 White Ants The status of white ants, in their relation to the Rubber tree, differs enormously in the different rubber-growing countries. In Ceylon and South India the white ant is not a pest ; in Malaya, Java, and Sumatra it is one of the worst pests with which the rubber planter has to deal. The explanation of this is simply that the species of white ant which attacks living trees generally, and has extended its ravages to the Rubber tree, viz. Termes gestroi, is not found in the former countries. In Ceylon Etttermes inanis has been found, on one occasion, in the hollow stem of a Rubber tree. The tree had been broken off by the wind, and several secondary stems had sprung up from the original stump. The white ants had attacked the broken stem from the top, and had established a nest in the wood, but did not touch the outer living tissues. The nest was scooped out, and the insects were got rid of by flooding the cavity with a solution of naphthalene in petrol. The common mound - building termites, e.g. Termes redemanni and Termes obscuriceps, often buQd a coating of earth over the bark, sometimes all round the tree and to a height of two or three feet. The insects feed beneath this covering, but they eat only the outer dead bark, and do not penetrate into the living cortex. Consequently they do not cause any direct damage. The coating of earth should be brushed off, a task which should be carried out by the tapping cooly. It has, however, been stated that Brown Bast is conveyed to the trees by white ants which devour the outer dead bark, and, if that is substantiated, it wiU be neces- sary to take steps to prevent them building this casing on the tree. That would entail the destruction of the white ant hills, and for that purpose the Universal White Ant Exter- minator should be used. It is useless merely to level or dig up white ant nests, or to pay special rewards for queens. Some of the insects are of course destroyed if a nest is dug up, but ordinary observation will show that a large proportion are left, — quite sufficient to reconstruct it. The removal of the queen, no doubt, retards the increase of population for a short time, but the termites soon evolve a successor. 226 THE RUBBER TREE chap. With the exception of the foregoing cases, white ants in Ceylon only attack Rubber trees which have previously been attacked by some fungus disease. The conditions in Malaya, Java, and Sumatra are quite different. In those countries, and in Malaya especially, the termite fauna includes a species, Termes (Coptotermes) gestroi, which has long been known to attack living trees, and has unfortunately included Hevea among its victims. This species was discovered by Haviland in Malaya, and the fact that it attacked living trees was recorded by him, but it was not untU Rubber estates were opened on a large scale that it became of economic importance. Termes gestroi usually attacks a tree below ground level. Like the majority of termites, it travels underground by means of narrow galleries, and when one of these galleries happens to meet a root of a Rubber tree the insects attack it. Lateral roots may be immediately attacked, or the insects may tunnel a gallery underneath the lateral until the tap root is reached, into which they penetrate. Once inside the tap root, the termites eat out galleries in the wood and advance upwards into the stem. The wood of the tree is hollowed out, and the cavity is filled with a comb which is bmlt of the excreta of the insects, and is, in fact, the remains of the wood of the tree after it has passed through their bodies. Ulti- mately the tap root is destroyed, the laterals hollowed out, and the interior of the stem becomes a termite nest. The affected trees may then blow over, or faU over during rainy weather ovnng to the extra weight of the wet foliage. In "wet weather Termes gestroi will appear on the Rubber tree above ground, and cover the trunk with a casing of mud for a height of several feet. Galleries are formed in the trunk immediately beneath the cortex, and passages from these extend through the bark to the exterior of the stem. On Kapok trees these passages are made from the exterior into the stem, but it appears to be undecided whether this occurs in Hevea. On the latter tree the termites have generally progressed within the tree higher than the mud casing extends on the outside, and on stripping the tree their galleries may be found in the wood immediately under unperforated bark. In Hevea this external occurrence of the termites is usually secondary, i.e. it will generally be found that when the mud vni PESTS 227 casing appears on the tree the roots have been attacked some time previously. As the work of destruction is begun underground, and Hevea can suffer considerable damage to its roots without any ill effect on the crown, no general sjrmptoms of an attack by Termes gestroi can be described. Hollow trees, trees with small holes in the trunlc which exude latex, and the occurrence of the external mud casing, may all be signs of its presence, but none of these is universally so. The mud casing, as iilready noted, may be constructed by ordinary mound- building termites which eat only the dead outer bark. But the occurrence of any of these signs, in a country where Termes gestroi exists, should be regarded with suspicion, and the roots of the tree exposed and examined. Like other species of termites, or white ants, the indivi- duals of Termes gestroi constitute several different forms or castes. Those commonly found in the nests are workers, soldiers, and young. There is also, somewhere in the neigh- bourhood, a queen, with the usual abnormally distended abdomen, and a much smaller king, while at certain times the nests contain, in addition, winged insects. The latter are the males and females, the workers and soldiers being neuters. When the winged insects leave the nest, they set up fresh colonies elsewhere, if they escape the attacks of their numerous enemies. The identification of the very numerous species of ter- mites is not an easy matter, and to the ordinary layman they all look very much alike. It is based, in general, on the form of the soldier. There is no difficulty in determining which is the soldier, in the case of Termes gestroi, as it possesses a pair of strong mandibles, and if one puts his finger in the nest it Mnll bite and remain attached. The mandibles are slender and red-brown, \yith black tips ; the head is oval and yellow- brown ; and the body white and somewhat parallel -sided. When the soldier bites, it exudes a drop of white milky fluid from an opening on the anterior part of the head. None of these points is pecuUar to Termes gestroi, but they may serve to prevent confusion with some of the common harmless species. The nests of Termes gestroi which are found in Rubber trees never contain queens or eggs. They are not the main 228 THE RUBBER TREE ' . chap. nests, but subsidiary nests. Hence it is of relatively little use to devote attention merely to the Rubber trees attacked, for that will leave the main nest untouched, and its in- habitants wiU invariably attack other tfees. The principal nest, the one which contains the queen and eggs, is situated in some dead log in the neighbourhood, and from it galleries ramify underground to the subsidiary nests in the living trees. These galleries run at varying depths, according to the character of the soil, being, on flat alluvial land, usually one to two feet below the surface ; they are about a quarter of an inch high, and an inch broad, and are lined with a thin layer of some red substance. The method of dealing with Termes gestroi, which was formerly proposed, was to follow up the underground run- ways or galleries from the free attacked to the log in which the principal nest was situated, and then to destroy the termites in the log by fumigating with the Universal Ant Exterminator. That was subsequently modified in the following manner. The nest having been located in a log or stump, presumably by examination of all the logs in the neighbourhood, this was isolated by a trench, three feet from the log, cuttiug across aU the run-ways. Tlie trench was then left open for a few days, during which time the insects rebuilt galleries connectiag the run-ways on either side of the trench. The log was then fumigated by boring auger holes ia it and pumping in sulphur-arsenic fumes, and each run-way on the outer side of the trench was also fumigated. Finally the attacked trees were fumigated, if the fumes pumped into the run- ways had not already reached them. The foregoing method failed to eradicate, or to stop the attacks of, Termes gestroi. It failed because it was a " piece- meal " method which did nothing to prevent attacks, and because it ignored facts of primary importance in the Ufe history of the insect. Termes gestroi does not live solely, or principally, on living trees. It feeds on dead wood just as well as on living wood. And its presence in a Rubber plantation is not due to any modern development on the part of the insect of a preference for Hevea, but to the abundance of dead timber and rotting stumps which are to be found there. vm PESTS 229 Both in Malaya and Java Termes gestroi is a compara- tively rare iasect in the jungle, where it inhabits dead or dying trees. Winged individuals from such localities, during their brief nuptial flight, reach a Eubber plantation, and settle down to found colonies in the rotting logs which so frequently abound there. In course of time these colonies produce other winged individuals, which establish new nests in other parts of the estate ; and iu a year or two numbers of colonies may be present before there is any evidence of their existence by attacks on the Rubber. Obviously, the only method of preventing this is the removal of all fallen timber and decaying stumps, i.e. the method of clean clearing. The piecemeal method of dealing with attacks as they arise loses sight of the fact that other logs are left which are capable of harbouring Termes gestroi ; and even if every Termes gestroi was eradicated from an estate by that method, one pair of winged insects could re-infect the whole estate, as Idng as the timber remained. Selective removal of timber has been advocated, those kinds being got rid of which are known to afford favourite nestiDg grounds for Termes gestroi. The number of such timbers is, however, fairly large, and there is no evidence that the termites will not inhabit any given timber if their more favoured kinds are wanting. The only safe plan is to remove and burn all timber. The Termes gestroi question presents an exact parallel to the root disease problem. In both cases the attack on the Rubber tree proceeds from an external base of operations, and ia both the external base is the same, viz. dead timber and decaying stumps. The solution is also the same in both — clean clearing. Peaty land presents especial difficulties, both with regard to Tertnes gestroi and root disease fungi, owing to the existence of buried logs. These must also be got rid of, by probing for them, digging them up, and burning. Where Termes gestroi has become estabUshed, particularly in old Rubber, fmnigation methods should be employed, in addition to the destruction of all timber. All nests in logs or stumps should be destroyed by fumigating. Rubber trees which have been hoUowed out by Termes gestroi should be treated by boring a hole into the trunk to reach the 230 THE RUBBER TREE hollow, inserting tlie nozzle of the fumigator, and luting it in with clay. After fumigation the hole should be plugged firmly with a cyHnder of wood, the outer end of which should be left level with the cambium. It is, however, extremely doubtful whether such trees will surArive very long. Root and Stem Borer of Heve i The larva of a large longicorn beetle, Batocera rubus, has been found on several occasions boring into the tap root, or the lower part of the stem, of Hevea in Ceylon. It appears to be generally distributed through the rubber-growing areas of that country, and cases of its attack on Hevea are periodically reported, but it has not yet caused any wide- spread damage. According to the recorded instances, only a single tree is attacked in each case. In the most general case the larva attacks the tap root well below ground, and bores a large gallery more or less up the centre (Kg. 36). The tree, if of moderate size, then behaves as though attacked by a root disease. The crown may become thin and the tree ultimately die. But most frequently the tree blows over, the root breaking ofE a few inches below ground. As a rule, only one larva is found in the tap root. In other cases the tree is attacked at or near the collar. Cavities are then eaten under the bark -and in . , ^ . , ^ tlie wood, or a gallery may be bored right mto the heart of the tree. These attacks may be dis- covered by the rotting of the bark at the base of the tree, or by an exudation of yellowish matter. In a number of recent cases the borer has been found Fig. 36.— Root bored by Batocera rubus. x J. ym PESTS 231 to attack the main stem of trees about twelve years old, above the tapping surface, from a height of about three or four feet to about seven or ten feet. The effect is then quite different from that of an attack on the root, the first sign, in the instances hitherto recorded, being the sudden death of all the leaves on the tree. Within two days the leaves curl and dry up, remaining attached to the twigs and retain- ing a pale green colour for a considerable time. The effect resembles that of a root disease, though the leaves do not turn brown readily, and the tree may be too large to be affected by a root disease in that particular way. The roots on examination are found to be quite healthy, and the stem appears normal. But on cutting into the stem it is found that the bark, though exhibiting no abnormal feature ex- ternally, is decayed internally, sometimes all round the stem, sometimes only in patches, for a length of three or four feet, from a short distance above the tapped surface sometimes as far as the first fork. The branches are not affected. Under the decaying bark are found large white grubs in shallow cavities about the size of one's hand on the surface of the wood. From these cavities galleries penetrate into the centre of the stem. The grub appears to feed on the wood inunediately beneath the bark, and eats out large areas, but to no great depth. The bark over these areas dies and decays, and this decay extends until adjacent patches coalesce and the tree is ringed. The death of the crown follows, as its water supply is cut off by the ringing and perforation of the stem. The galleries in the stem are usually narrow and oval in section, with the longer axis vertical. They thus differ from the large gallery which the grub makes in the root. The explanation of the difference would appear to be that in the root the grub feeds on the wood in the centre and so enlarges its gallery, while in the stem it feeds beneath the bark, not in its gallery. In either case the gaUery which the insect makes when it emerges is circular in section. Large numbers of grubs may be found in a single stem. The larva (Plate VI., Mg. 2) is a large fat grub, up to three inches in length, creamy-white in colour, somewhat flattened above and below, segmented, and tapering from head to tail. Its head is triangular, dark brown or black, 232 THE RUBBER TREE ^"^^^ and small, and is often partly retracted and more or less hidden hj the border of the following segment. The adult beetle is large and conspicuous (Plate VI., Fig. 1). In colour it is dull olive-brown, with reddish spots on the. wing covers, which are also thickly covered on the anterior part with minute black spots. There is a small, white, shield-shaped patch at the junction of the wing covers, and a broad white band extending longitudinally along each side of the body. The antennae are long and stout, and swollen at the joints ; thsy extend backwards beyond the extremity of the body. The average length of the beetle is nearly two inches. The hf e history of the beetle, in its relation to the Rubber tree, has not yet been determined. It is assumed that the eggs are deposited in cavities or cracks in the bark, or in wounds, and that when the young larva hatches out it bores into the tree. But how it efiects an entrance, eighteen inches or so below ground, is still obscure, the only suggestion hitherto made being that the larva fails to penetrate through healthy bark at the collar, and works its way down in the soil until it finds a diseased or broken lateral root. This, however, would seem to require that root attacks should be the exception, whereas they are actually the rule. Green suggests that the normal mode of entry of the grub is through diseased bark, whether above or below ground. In many of the cases I have examined, however, the root has not been more decayed than it would be expected to be after having been tunnelled for several months. The grub has been found in roots attacked by Brown Root disease and UstuUna, but it also occurs in roots which are to all appearances sound. The attacks on the upper part of |the stem have not been 'associated with any known disease. The period taken by the larva to attain its full size has not been determined, but it is probably a lengthy one. Larvae have been kept under observation for five or six months, without any change ia size being observed. On the other hand, the final stages of transformation are rapid, the change from larva to beetle occupying about a month. The damage to the Rubber tree is of course done during the extended larval period. The larvae have been found in the roots of Hevea stimips yni PESTS 233 left in the ground after thinning out. These stumps, there- fore, afiord a breeding ground for the beetle. The afiected part of the stems of dead trees should be burnt at once. Until more is known about the mode of attack preventive measures cannot be devised. Boring Beetles in General The list of different species of boring beetles which have been found in dead stems of Hevea is a long one, but there is no doubt that, with few possible exceptions, these beetles have entered the stems after they were dead or diseased. Green, in 1914, enumerated twenty-three species, but, as far as the planter is concerned, only two of these can be said to be of importance, viz. Xyleborus perforans in Ceylon, and Xyleborus farvulus in Malaya. The bore boles made through the bark and into the wood by these species of Xyleborus are of small size, about a milli- metre (one-twenty-fifth of an inch.) in diameter. They thus resemble the boles made by the Shot-hole borer of Tea, XyMxyrus fomicatus, which, attacks living Tea stems ; and the beetles, to the layman, are very similar to the latter species. Hence their appearance in Hevea stems is liable to cause some alarm, seeing that they are so closely allied to a species which is a well-known pest of Tea. Xyleborus perforans has long been known to attack diseased stems of cultivated plants in Ceylon. It bores into the canker patches on diseased Cacao stems, and it was at first considered to be the cause of the Cacao Canker. Similarly, it soon discovers and penetrates into patches of Claret-coloured Canker, which are caused by the same fungus, on Hevea stems. It appears to have a particular liking for bark which has been attacked by that disease. It also attacks stems killed by Die-back, and, sometimes, by Pink Disease, or green twigs which have died back from any cause. Scorched trees, especially if only lightly scorched, suffer severely from its attacks, and, frequently, the presence of the borer is the first visible sign that a tree has been injured by the fire. Trees which have been injured by others ffJling against them during the process of thinning out are also liable to be attacked on the bruised area. 234 THE RUBBER TREE «=^ Wood which has been exposed by tapping wounds is not usually attacked by Xyleborus perforans, but, on the other hand, wood exposed by cutting out canker patches very frequently is. Bark killed by Brown Bast does not appear to be attacked, except in cases where the disease extends to the wood, and then the stem may be riddled. After scraping for Brown Bast the exposed cortex appears only to be attacked if it dies back to the wood. The action of Xyleborus parvulus in the Federated Malay States, according to the accounts given of it, is similar to that of Xyleborus perforans, but, in addition, it penetrates into Hevea stems through stubs left by bad pruning, or where branches have been broken off. It would appear self-evident that no beetle can bore through the healthy laticiferous cortex of Hevea without causing latex to flow ; and if latex exudes the insect must retreat or be smothered by it. Such penetration would only be possible if the beetle were furnished with some secretion which coagulated the latex in the latex vessels as it bored through them. That any of the borers known at present pos- sess that power is more than doubtful, as cases have frequently been observed where beetles which attempted to enter a tree have become embedded in rubber in the hole. In attacks of Claret-coloured Canker, where the disease does not at first extend right through the cortex to the wood, borers will penetrate through the outer diseased layers, and may continue into the healthy tissue beneath, but they are then driven back by the exuding latex. Attacks by borers on healthy bark are by no means unknown, but they are generally unsuccessful. In one instance, after thinning out, a large number of Xyleborus perforans hatched out from the felled Rubber logs and stumps, and these immediately attempted to enter the standing trees. They had apparently become accustomed to Rubber bark and wood. AJaother similar occurrence presented a peciiliar feature for which no adequate explanation can be offered. The beetles in this case did not penetrate through the outer stone-cell layer of the cortex, and consequently were not hindered by a flow of latex, but, nevertheless, each one died in its hole with half its length projecting from the stem. In general, Xyleborus only attacks Hevea when the bark is vni PESTS 235 diseased. There are, however, cases where these beetles do appear to have bored through healthy bark, and in such cases the apparent explanation is that the latex was, for some reason, stagnant, or iinable to flow, at the time of attack. Overtapping has been suggested as a cause which would produce such an effect, but that would seem extremely doubt- ful. Moreover trees often cease to yield without any evident cause, and they are not necessarily then attacked by borers. Nor are they generally attacked when they cease to yield latex because of root disease. Further investigation is required on this point. Bark which has been severely attacked and penetrated by borers should be cut out, and the exposed wood treated first with Solignum, or Jodelite, etc., and then tarred. Where exposed wood is attacked it should be dealt with in the same way. If only a few scattered holes are present in the bark each should be tarred over. Bark-eating Caterpillars Several species of caterpillars feed on the outer corky bark of Hevea, or on the lichens and algae which grow on it. As a rule, they do not penetrate into the living cortex and conse- quently do not cause any appreciable damage. One of these weaves a small silk sheet, to which are fastened small fragments of bark and the excreta of the caterpillar. This sheet is attached flat to the bark, and the caterpillar lives and feeds beneath it. The mature insect is a small Tineid moth, Comocritis pieria. Another Tineid caterpillar constructs a tube, about one- tenth of an inch in diameter, and up to four inches or so in length (Fig. 37). The tubes are formed of interwoven silk, and are covered on the outside with minute fragments of bark. At first sight the stem appears to be covered with short lengths of string. Each tube is fixed at one end in a crevice in the outer bark, but is free for the remainder of its length, and changes its position as the caterpillar, which is normally situated at the open end, moves over the bark. The caterpillaf , in fact, browses over the bark like a cow at the end of a rope. This species has apparently not been identified. 236 THE RUBBER TREE '=^- The first of the above-mentioned caterpillars can be got rid of by simply brushing them ofE ; but in the case of the second the tubes should be coHected and destroyed as the caterpillars reascend the tree. More serious damage has been caused in Malaya by a bark-eating caterpillar, which attacked both tapped and untapped bark and caused small irregular wounds. The caterpillar, which was not identified, was about one inch in length and one- tenth of an inch in breadth, brownish - red, each segment being pro- vided with a pair of long, thick, clubbed hairs, stand- ing out from the body and projecting downwards, so that when at rest it had the appearance of a small centipede. It was not, however, sufficiently numerous to warrant any method of treatment other than hand picking. In Sumatra it is re- corded that caterpillars belonging to the group usually known as Bag worms, or Case worms, have attacked renewing '^ *■ bark about a month old, two and a half to three centimetres above the tapping cut, and have caused holes resembling neglected tapping wounds. The particular species concerned in this case was Psych& {Acanthopsyche) sneUeni. It builds a conical house, about fifteen inilUmetres high, covered with minute fragments of bark (Plate VI., Fig. 3). As a rule this species feeds on the dead bark and lichens, but in the case recorded some of the caterpillars had extended their operations to living bark. The female insect does not leave its house, and the eggs are laid within the conical case. Consequently collection Fig. 37. — Tubes of a bark-eating caterpillar. PESTS 237 and destruction of the cases destroys all the females and eggs. Mites The occurrence of mites on nursery plants of Hevea was first recorded by Arden in the Federated Malay States. Some years later it was again noted by Ridley and Derry in Singapore. The leaves of the seedlings became irregularly twisted and distorted, one side of the leaflet often being shorter than the other, and the leaflet curved to one side. On examining the under side of the leaf the tissue between the veins was seen to be swollen, the veins appearing green on a grejdsh background. The mites occurred on the under side of the leaf, but were not abundant. They were white, semi- transparent, with three brownish marks on the back. The damage was confined to seedlings, especially those which for any reason were weak. Overcrowding in the nursery was said to be, in great part, a condition under which injury occurred. Frequently the lowest three or four leaves were attacked, after which the leaves which subsequently appeared developed normally. The mite was said to be rarely seen on well-grown adult trees, and it did not cause any injury on such. Bernard recorded an attack by mites on nursery plants of Hevea in Java in 1907. The leaves were distorted, one side remaining normal and the other becoming somewhat shrivelled and crumpled with its margin curled underneath. The very young leaves did not develop, and the apex of the stem was swollen. The mite was wMte, about one-hundredth of an inch in length. Bernard also recorded the attack of a different mite on trees eight years old. The effect on the young leaf was similar to that already described, while, when the leaves were older, their margins became dry and transparent. This attack occurred on trees which had wintered late, and whose new leaf, in consequence, developed during very dry weather. More recently it has been recorded that on several estates in Java mites have caused a fall of young leaf immediately after wintering. Richards states that, in the Federated Malay States, the Rubber leaf mite occurs on every estate, but it does not cause 238 THE RUBBER TREE chap. serious injury unless the plants are growing under unfavour- able conditions. The effect varies, from mere distortion of the leaves, to repeated defoliation, which finally results in the death of the plant. This variation depends on the virulence of the attack, the vigour of the plants, and soil and weather conditions. The Rubber leaf mite usually attacks nursery plants, which may be checked and stunted, or even die, in conse- quence. When it attacks plants in young clearings they may become sickly, stunted, and misshapen, so that frequent supplying is necessary, while, in one instance, several hundred five-year-old trees were lost through exhaustion and die-back following an attack by these insects. It is capable, therefore, of becoming a serious pest under certain conditions. The mites occur in large numbers on the under side of the leaves, where they feed by puncturing the epidermis and sucking out the cell sap. The life cycle of the mite is short, from five to seven days, and each female lays fifty or more eggs. Mite attacks may be followed or accompanied by the attacks of stem and leaf fungi, notably Helminthosporium, Gheosporium, Phyllosticta, and, later, Diplodia. In Java removal and destruction of all the leaves attacked, or of the upper part of the stem, is said to have checked this pest in the case of nursery plants. Dusting the plants with iiowers of siilphur has also been recommended. In the Federated Malay States emphasis is laid on the improvement of soil conditions by draining, manuring, and cultivation. Where the attack is severe, spraying is neces- sary, and it has been found that a lime-sulphur wash contain- ing two pounds of sulphur per 100 gallons gives satisfactory results. The plants should be sprayed twice, with an interval of ten days, and subsequently any nurseries or young plants which show signs of re-attack should be sprayed once in three or four weeks. Locusts In Ceylon the Spotted Locust [Aularches militaris) occasionally appears in swarms in some districts, and eats the leaves and gnaws the green stems of Dadaps. It has been reported to have attacked young Rubber in one instance, and vm PESTS 239 partially defoliated it, but injury to Hevea by these insects is practically unknown in that country. In Malaya an outbreak of locusts {Pachytylus sp.) began in 1912, and has continued up to the present time (1919). They have not, however, attacked Hevea, though some damage has been caused through the breaking of the branches of that tree by the weight of the swarms of fliers which have a tendency to settle on Rubber trees at night. This species feeds chiefly on wild grasses, and consequently weedy estates afford them suitable feeding grounds. More serious damage has been caused in Java by a locust, Cyrtacanthacris nigricornis, which, previously known to attack Cofiee, turned its attention to Hevea about the year 1914. In 1915 it occurred in large swarms, and was still abundant in 1916, but the plague ceased in 1917. Teak forests formed its headquarters, and from these the winged insects spread to adjoining estates, attacking Hevea, Castilloa, Ficus, Dadap, Coffee, and Cacao. On estates bordering on the teak forests young Hevea was eaten bare, and stood leafless for some months. The twigs were not gnawed. Some plants were defoliated twice and died. Young plants especially were killed, while trees two to three years old produced a large number of weak branches after defoliation, and consequently an abnormal crown, which, however, could be improved by drastic pruning. The damage was greatest nearest the teak forests ; as the insects travelled further afield they scattered, and the injury then caused in any particular locality was small. Locusts in the hopper stage can be combated by driving the swarms into pits, or bag traps, placed in their line of march, or by poisoning them by sprajdng the vegetation on which they are feeding with arsenite of soda. A solution which has been found efficacious in Malaya is one pound of arsenite of soda, dissolved in four gallons of water, with the addition of two pounds ©f molasses. Five cigarette tins of arsenite of soda are placed in a kerosene tin (4 gallons) full of water and boiled for ten minutes or a quarter of an hour. Ten cigarette tins of sugar, or molasses, are placed in another kergsene tin, which is then filled up with water. One-fifth of each of these solutions is poured through a strainer into a sprayer which will hold three gallons, and the sprayer then filled up with water. Vegetation sprayed with arsenite of 240 THE RUBBER TREE -^^^^ soda is poisonous, and precautions must be taken to prevent cattle, etc., feeding on it. In the instances recorded the locusts which have attacked Rubber have been insects in the final or winged stage, not in the larval or hopper stage. In such cases the foregoing methods are inapplicable. Where the outbreak is small poisoned baits may be used, placed in heaps among the plants. Green recommends a bait made of one part Paris Green, two parts of salt, and forty parts of fresh horse dung, with sufficient water to make the mixture soft without being sloppy. The bait recommended for crickets (p. 245) may be used, if horse dung is unobtainable. But in a continued plague of locusts the insects should be attacked in the hopper stage. Where locusts congregate on definite patches on cultivated land for the purpose of laying their eggs (which are laid in holes in the ground) they may be swept into bags and destroyed by sinking the bags in water. The ground should then be broken up to a depth of six inches, and quicklime forked in. Scale Insects Several species of scale insects have been found on Hevea, but few of them in any quantity ; and up to the present no serious damage has been caused by them. Green has recorded the occurrence of Asterolecanium pustulans on Hevea in Ceylon, and states that it is responsible for an unhealthy condition of the stem. The insects occupy small depressions in the bark, and, when present in consider- able numbers, the bark assumes an unhealthy nodular and hidebound condition, and tapping may be interfered with. But this occurrence would appear to be very rare. The scale insects commonly found on Hevea leaves and green stems are Lecanium nigrum, a purple-black convex species about one-fifth of an inch long (Plate VI., Fig. 8), and Lecanium viride, a somewhat flat green scale about the same length. They occur on the leaves, often congregated along the lines of the veins, or they may thickly encrust, the terminal green stems. Attention is usually directed to their presence by the growth of the black " Sooty Movilds " over the leaves and stems (see p. 94). Plate VI. PF.STS OF HFA'EA PESTS 241 It would scarcely be possible to treat these insects by- spraying methods in the case of Hevea. Fortunately they are, as a rule, kept in check in Ceylon by parasitic fungi. One fungus, Cephalosporium Lecanii, attacks the commoner species and kills them, subsequently growing out as a white fringe round each scale (Plate VI., Fig. 9). Another fungus, Hypocrella Reineckiana, grows over each scale in a hard cushion-like mass, which is at first red-brown or yellow- brown, often with a glaucous bloom, but becomes black when old (Plate VI., Fig. 10). Both these fungi are parasitic only on the scale insects ; they do not attack the tree. They should be left undisturbed when seen. Ants The red ant {Oecophylla smaragdina), though not a pest of the Rubber tree, can become a decided nuisance on a Rubber estate, so much so that coolies will refuse to work in fields heavily infested with them. This well-known ant constructs its nest in the foliage of the tree by binding together living leaves, and if the nest is disturbed it attacks the aggressor and bites vigorously. It frequents the stem of the tree on which the nest is situated, and if present in large numbers may cause inconvenience to the tapping cooly. It is, however, when the trees are wintering that these ants make their presence (literally) felt to the utmost. The nests then fall to the groimd when the leaves wither, and large areas may be covered with hordes of red ants, only too ready to attack any one who passes. These ants may be got rid of by continually burning the nests. Pests of Seedlings and Young Plants COGKCHAFER GrUBS The grubs of various species of Cockchafers, or May Beetles, have been found to attack the roots of young Hevea plants, whether stumps or seedlings. These are, in general, large, white, fleshy grubs, wrinkled towards the head end. 242 THE RUBBER TREE ™^^ but smooth towards the hinder part, which is generally swollen and curved round towards the head (Plate VI., Kg. 5). They are frequent in soil where vegetable matter has recently been buried, as, for instance, among Tea in the holes in which pruniugs have been buried, or on land formerly in grass, where the grass has been turned in. The eggs of the beetle are laid in soil of this character, and the grubs burrow under- ground to the roots of neighbouring plants. In Malaya the roots of Hevea seedlings have been at- tacked by the grub of a cockchafer beetle allied to Tricho- lepis lactea. The grub is about two and a half inches long, creamy -white, shmy, slightly hairy. The adult beetle is about one and a half inches long, snowy-white, with rather darker stripes along the wing cases. Collection of the grubs and beetles for cash has been suggested as a means of getting rid of it. In Ceylon the cockchafer grub which attacks the roots of young Rubber plants is usually the grub of Lepidiota pinguis. This was formerly known as a pest on Coffee estates, and does serious damage to Cinnamon. It also attacks Tea. The grub is of the usual shape and up to three inches in length. The beetle is rather more than two inches long, duU brown, with a covering of greyish hairs (Plate VI., Fig. 7). The beetle lays its eggs just below the surface of the ground, and the grubs burrow down and attack the roots of the plants. The tap roots of Hevea stumps have in some cases been eaten clean off up to within an inch of the surface of the soil, and in one instance three thousand plants were lost in one clearing, as many as five or six grubs being found in each hole. Older trees are apparently not attacked. Nitrate of soda, applied at the rate of one to two ounces for each plant, is said to drive away the grubs. Vaporite has also been recommended, about one to one and a half ounces forked in about six inches away from the stem of the plant. With the latter substance the grubs are said to come to the surface, and crawl away or die. Vaporite should not come in direct contact with the roots. Dead plants should be dug up and search made for the grubs round them and neighbouring plants. In Java a large number of plants a few months old vm PESTS 243 were killed in one clearing by cockchafer grubs (Oerets). The side roots were eaten off, the cortex of the tap root eaten away, and in some cases holes were gnawed in the wood. The species in this case was Hohtrichia Jeucophthcdma, a dark brown, or red-brown, shining beetle, about an inch in length. The colour is darkest on the head. The attack occurred on Hevea interplanted with Bohusta Coffee, in a clearing which was clean weeded, but had been badly burnt off. It was proved that the grub preferred Hevea, to Coffee, but would attack many kmds of plants, and more particularly favoured succulent plants, including common weeds. Large numbers of grubs were found under decaying Ficus wood and rotting bamboo leaves. The beetle flies at night, and buries itsdf in the soil, to a depth of about four inches, during the day. In the instance recorded no beetles were found in the soil in the clearing infested by the grubs, but they occurred in a neighbouring field of old Coffee where the ground was shaded. To avoid attacks of Hohtrichia leucophthalma it is recom- mended that the ground should be cleared as far as possible of all decaying branches, leaves, logs, etc., before the time when the adult beetles begin to appear, so that possible breeding places are got rid of. In Java the beetles are found on the wing durir^ the first months of the wet season, October to January. If a clearing is attacked the more succulent weeds should be allowed to grow, as the grubs wiU feed on these in preference to the Hevea ; it may be advisable to sow seeds of a succulent plant, e.g. Amaranthus gangeticus. Search should be made in liie vicinity of the clearing for the places where the beetles hide during the day, and as many as possible should be caught, so that the pest may not spreau to other clearings. Bark-eating Beetles A loi^corn beetle, Moechotypa verrucicoUis, is said to damage the stems of young Hevea trees, or of stumps shortly after planting out, by gnawing off the bark. The observa- tions on this point, however, are not in entire agreement. Green records that the injured stems showed irregular patches where the bark had been destroyed, in some cases 244 THE RUBBER TREE °^' completely ringing the tree. No latex had exuded from the wounds ; consequently, the stems had been dry when attacked, and the roots showed the presence of the root disease fungus of Rubber stumps, viz. Botryodiplodia Theo- bromae. When the beetles were placed in a cage with a healthy young Hevea, one individual climbed up the stem and fixed its jaws in the tender bark ; but when the latex exuded it abandoned the attack, and devoted itself to getting rid of the rubber adhering to it. After a week's confinement without other food the beetles still refused to touch the living bark. Rutherford recorded a case in which the beetles had attacked stumps planted out a month previously, and noted that they had chiefly eaten the bark on plants which were not likely to grow, though they had also been found on healthy stumps. From his experiments he concluded that, while the beetles can undoubtedly eat the bark in spite of the flow of latex, they prefer dry bark. The beetle is about an inch long, of a reddish -purjple colour, with a greyish area in the form of an X on the wing covers (Plate VI., Fig. 6). The under surface is pinkish. Rutherford recommended that the stumps attacked should be sprayed with Lead Arsenate. Rhinoceros Beetles The Fork -horned Rhinoceros Beetle, Xyhtrupes sp. (Plate VI., Fig. 4), attacks stumps soon after planting out, as soon as the shoots appear. The young shoots are bitten off, and the process may be repeated as often as new shoots appear, until the plants are clubbed and worthless. Pratt records that he has seen 300 acres of Rubber, eighteen months old, without a single green leaf owing to the attack of this beetle, and that on another occasion 1000 acres suffered in the samei way. The beetles rest during the day on old Rubber in the neighbourhood, or in jungle. The attacks are prevented by enclosing each plant in a cylinder made of ordinary newspaper. A full sheet is rolled up into a cylinder the height of the paper and about six inches in diameter, and fastened with three pins. These PESTS 245 are placed over the stumps, and j&xed in position by means of three thin stakes on the inside. Swarming Caterpillars Swarms of caterpillars, which had originally developed on grass, etc., have been found to pass on to Rubber after their original food had become exhausted. In the Federated Malay States an instance has been recorded where cater- pillars {Spodoptera sp.) first of all developed in an area which had previously been flooded and was consequently covered with rank grass. The resulting moths laid their eggs in a neighbouring young clearing, planted with stumps and seed at stake. The next generation of caterpillars ate up all the available grass and weeds in the clearing, and then attacked the young Rubber, defoliating it in a few days, and gnawing the green stems, over an area of several acres. Such an occurrence is not likely to happen except in young clearings. Where swarms of caterpillars appear .among young Rubber, their food plants, grasses, etc., should be sprayed with some poison which will not damage the Rubber. But perhaps one ought to regard such occurrences as an argument in favour of clean weeding. Crickets Crickets often give trouble in nurseries by biting ofi the young plants one or two centimetres above the ground. These insects live in holes in the ground, where they remain during the day, emerging at night to attack the plants. The remains of the plants may be found in their burrows. Heavy rains drive them out of their holes, and it has been suggested that advantage should be taken of that circum- stance to collect them, or the nurseries might, if possible, be flooded for a short time. Green recommends that dilute Phenyl should be poured down the burrows. These insects may be killed by the use of poisoned baits. One such, recommended in Java, is made by chopping up young maize plants and mixing a little treacle and five grams of arsenic or Paris Green with each pound of the 246 THE RUBBER TREE ^^ chopped plant. This is then placed in small heaps in the niixseries. Bran may be used instead of chopped green material. In the Federated Malay States a large cncket, Bractiy- trupes achatinus, saws through young plants, leaving a stump one to three inches high. Its attacks have been circumvented by surrounding the yoimg plants with cylinders of paper, as described for the Fork-horned Rhinoceros beetle (p. 244). Slugs Early in the history of plantation Rubber in the East it was found that slugs ascended the tree and drank the latex, either as it ran down the tapping cut, or after it had collected in the cup. In Ceylon the species which acquired this habit is a brown slug, Mariaella dussumieri, wMle in Java a different species, Parmarion reticulMus, has adopted the same practice. As long as these slugs confined themselves to drinking the latex their presence was disregarded. The chief result in the case of the Ceylon species was said to be a loss of scrap rubber. Keuchenius, however, has shown that where these slugs are abundant the loss of rubber, owing to their consumption of latex, may be fairly large. He calculates that if each slug drinks a cubic centimetre of latex per day, then ten thousand will cause a loss of 150 pounds of dry rubber per month ; and he instances one case in which over 37,000 slugs were collected in a period of three weeks. In young Rubber these slugs have caused great damage by an entirely different method of feeding. They cUmb up the stems during the night and eat off the terminal bud. New buds then develop, and these are in turn bitten off, until the plants assume the appearances shown in Fig 38, which is a photograph, nearly natural size, of the lead- ing shoots of three plants after repeated attacks. On the shoot in the centre the apex is clubbed and consists of a number of arrested shoots, while lower down the stem the leaves have disappeared, and side -shoots, some of them similarly clubbed, have developed, though the stem was stiU green. The apices of the other two are similar, but each stem has developed several side-shoots ; the tops of these side- vm PESTS 247 shoots have also been attacked, and on one of them buds have appeared lower down and are giving rise to branches. Fia. 38. — ^The eSeot of slugs. Under normal conditions each of the leaders photographed would be a straight green stem, growing only at the apex ; 248 THE RUBBER TREE but in each case the apex has been converted into a cluster of short shoots, most of which have not been permitted to develop further, while on those which have temporarily escaped injury and grown for a short distance the same process is being repeated. This may be continued until the plant dies. In any case the damage is serious, as the develop- ment of the plants is arrested, and they may be so distorted as to be worthless. These slugs feed chiefly at night. Hence they are not generally observed in the act, and the injury may be attri- buted to insects. During the day-time they may be found under dead leaves, etc., round the trees, or on the underside of living leaves on the tree itself. In Ceylon they were found climbing the stems in the evening. Plants which had branched were not severely attacked, those which suffered most being the single-stemmed trees ; the latter, after wintering, were not permitted to come into leaf again, every fresh green shoot being nibbled off, and the green epidermis gnawed. The slugs probably drink the latex because of the sugar which it contains ; and they appear to attack the buds in order to obtain the latex. Mariaella dussumieri is a yellowish-brown slug, mottled with darker dots and streaks. It is usually two or three inches long, but is said to grow to eight inches in India. The mantle, i.e. the fleshy fold which covers the middle of the body, bears two narrow ridgeg. Its minute shell is entirely hidden by the mantle. A' figure of it is given on Plate VI., Fig. 11. Parmarion reticulcdus bears a small, thin, shield-like shell on the mantle. Collection of the slugs has proved the most practicable method of dealing with this pest. Dead leaves, etc., should be raked away from the bases of the stems, and the field clean weeded. The heaps of dead leaves may be utilised as traps for the slugs. The latter may be killed by dropping them into a weak solution of Izal or some similar soluble disinfectant. CHAPTER IX miscellanea The Effect op Preservatives on Renewing Bark In the operation of tapping, the dead bark, which is the natural protective layer of the tree, is removed, and the delicate inner tissue of the cortex exposed. The tree then immediately begins to form a cork cambium a short distance beneath the exposed surface, which cuts off the outer layers of ceUs as a new protective layer of dead brown bark. This bark layer is at first about 0-4 millimetre thick (about one- sixtieth of an inch), but its thickness is subsequently increased by the action of successive cork cambiums. In alternate-day tapping at Peradeniya this bark layer is completely formed about ten days after tapping, while its thickness is about 0-4 milUmetre immediately above the cut, 0-7 millimetre one inch above, and up to 1-2 millimetre three inches above. Any preservative or disinfectant applied to the renewing bark is liable to penetrate to a depth dependent upon the strength employed, and it may penetrate right through to the wood and cause wounds. Consequently, before using any of these substances it is necessary to make experiments to determine what amount of injury they can cause. It would be expected that the area most liable to injury would be the zone immediately above the tapping cut which is not yet covered by a new bark layer. Any injury caused by the application of preservatives should, therefore, if it extends to the wood, be evident as a narrow wound parallel to the cut. Above that zone the cortex is protected by the dead bark layer, the thickness of which increases the further it is from the cut : and the substance applied must penetrate this bark layer, before it can attack the underlying living 249 250 THE RUBBER TREE ™^ tissues. Hence it would be anticipated that the further we ascend from the tapping cut the less is the probability of injury. In actual practice, however, conditions are some- what different, because the outer brown layer cracks, and consequently renders the underlying tissues more accessible immediately beneath the crack. Hence it may happen that the penetration at a height of three inches from the cut, where the brown layer is usually cracked, may be greater than ^at points below that, untU the actual cut is reached, though it may be confined to narrow Hnes corresponding with the cracks. But, owing to the greater thickness of the renewing bark, the risk of causing a wound at a distance from the tapping cut is less. The possibility of injury, i.e. of wounding, depends also on the. thickness of the layer of cortex left overlying the cambium after tapping. No wounding has been observed with the substances ordinarily in use where this layer was 1-5 millimetre thick. The phenomena observed in the treated cortex may be sununarised as follows : (1) The production of a network of shallow furrows on the surface of the living cortex, beneath the outer dead bark scale, indicating a deeper penetration through the cracks in the latter. (2) A blackening or brown- ing of the tissues into which the liquid has penetrated ; these tissues are' killed and added to the dead bark scale. (3) A general greening of the living cortex in the majority of cases ;^ this is a well-known characteristic of the action of tar pro- ducts on plant tissues. In the cases in which the penetration is greatest it is usually not uniform, i.e. not to the same depth, all j;he way down the tappiag surface. Ordinary Brimolinum, for example, when used pure, may penetrate to a depth of one millimetre, three inches above the cut, but lower down the penetration becomes less and less until the actual cut is reached, when it again increases. It would appear that the extent of the penetration is dependent on the structure of the cortex. Under the dead bark scale the stone cell layer appears to be the more easily penetrated, the layer in which the latex tubes are continuous being untouched. Hence the penetration is deeper in the upper parts where the stone cell layer is thicker, and decreases downwards. On the tappiag IX MISCELLANEA 251 cut, however, which was unprotected at the time of applica- tion, the penetration is again greater, and extends into the latex layer. Consequently, when a liquid penetrates deeply, a narrow depressed zone appears at the position occupied by the tapping cut at the time of application, and in a longitu- dinal section of the cortex the position of this zone is marked by a concavity or sinus. It is this depression which should decide the question whether a given preservative is Ukely to cause injury. A penetration of a millimetre on the tapping cut, where the remaining cortex is only 1-5 millimetre thick, is likely to prove more serious than an equal penetration into renewing cortex, 3 miUimetres thick, three inches or more above the tapping cut. The breadth of this zone varies with different preservatives, the maximum observed being 5 miUitnetres (one-fifth of an inch). The details given below concerning different preservatives were obtained by experiments on trees tapped on alternate days by a siQgle cut on one-third or one-quarter of the circumference. The thickness of the cortical layer left overlying the cambium was, in general, 1-5 millimetre. The apphcation was made after the collection of the scrap on the day following the tapping. The extent of the penetration was determined by microscopical examination and measure- ment ten days after the application, tapping having been continued during the whole time. The renewed bark was in aU cases normal, and no exudations of latex were caused. The phrase " no penetration at the tapping cut " means that the thickness of the scale formed over the most recently tapped zone after the application was not greater than that which is usually formed there, i.e. there was no extra bark formation due to tiie substance applied ; the depth of pene- tration in such cases did not exceed 0-3 millimetre (one- eightieth of an inch). Coal Tab and Tab Mixtures Above the tapping cut coal tar does not penetrate through tite dead bark, but where this is cracked it penetrates into the living cortex to a depth of 0-3 millimetre in narrow lines ; hence the surface of liie cortex is strongly furrowed. At the 252 THE RUBBER TREE °=^ tapping cut tar penetrates to a depth of 0-7 millimetre (one- thirty-fifth of an inch) : there is a distinct sinus in the longi- tudinal section of the cortex when examined microscopically. Where a layer of cortex, 1-5 millimetre thick, is left overlying the cambium, tar will penetrate half-way through it at the tapping cut, but elsewhere the penetration is negligible. A mixture of tar and taUow, in the proportion of 5 parts tar to 95 parts tallow, does not penetrate through the dead bark layer, and the surface of the underlying cortex is only slightly furrowed beneath the cracks. There is no penetra- tion at the tapping cut. Tallow has been largely replaced by liquid fuel, owing to the high cost of the former. Experiments with liquid fuel alone showed no penetration beyond the. thickness of the normal bark layer, either above or at the tapping cut. A mixture of 20 parts tar and 80 parts liquid fuel showed no penetration through the bark layer at a distance of an inch above the tapping cut, and no penetration beyond the normal thickness of the bark layer at the tapping cut. A mixture of 80 parts tar and 20 parts liquid fuel showed no penetration through the dead bark layer one inch above the tapping cut, but at the cut the penetration extended to 0-8 millimetre, and there was a distinct sinus in the longi- tudinal section. The efEect of this mixture is similar to that of pure coal tar. From the foregoing results it . would appear that the penetration of tar and Squid fuel mixtures at the tapping cut increases as the proportion of tar is increased. It may, how- ever, be noted that liquid fuel is not necessarily of constant composition, and it is possible' that different samples may vary in their action on renewing bark. Tar and tar mixtures have been applied to renewing bark as a general protective against Black Thread and other diseases. But, in general, they have been applied at long intervals, say once a month, and in that case the part most liable to infection is left unprotected between the periodic applications. It is iirged that they cannot be applied after every tapping, because they take longer to apply than the more fluid preservatives, and they may clog the tapping knife at the next tapping, and so lead to an undue consumption of bark and perhaps contamination of the latex. A mixture of MISCELLANEA 253 20 per cent tar and 80 per cent liquid fuel has, however, been used on one estate for over two years, and is applied twice a week ; and from Java it has been reported that pure coal tar has been applied regularly after every tapping. But for regular preventive painting against Black Thread the weaker solutions of Brunolmum, etc., are more easily applied. In experiments carried out at Peradeniya with tar and tar luixtures no exudation of latex was caused. Such exudation does, however, occur on estates. In one instance it followed an application of 10 per cent tar and 90 per cent liquid fuel, and in another an application of 40 per cent tar and 60 per cent tallow. This exudation of latex may occur up to a height of four inches above the tapping cut. It frequently tai^s place at the edge of small tapping wounds, but it also occurs from unwoujaded cortex. No injury appears to foUow this, and it is generally regarded as negligible. Tar and tar mixtures are often applied too thickly. AU that is required is the thinnest possible smear. It should not he so thick that it melts and rims down to the cut. WTien tar and tar mixtures are applied to patches attacked by Claret-coloured Canker, without first excising the diseased bark, the disease continues under the tar layer. That fact was well known when Cacao Canker first became prominent, and it was that which led to the universal condemnation of tar in Ceylon. • Not only does the disease flourish beneath the t&r, but the protective covering hinders the drying out of the canker which should occur in the dry weather. Tar or tar imxtures may be applied to canker patches after the cankered bark has been excised, but if efficient supervision cannot be exercised, it is better to use Brunolinum, JodeUte, etc., as scamped work is then more eaaQy detected. Old wounds which extend to the wood should be tarred periodicallY, say once a year. Tar and tallow does not prevent beetles boring into the exposed wood, especially on recent canker wounds. Where beetles bore through into tarred wood, wounds should first of all be painted with So%Dum, or Brunolinum, etc., and tarred when that is dry. 254 THE RUBBER TREE c^^ Brunolinum The original Brunolinum (ordiaary Brunolinum) was not miscible with, water alone, but required the addition of soft soap. This has now been replaced by Brunoliiium Plantarium, which mixes with water without any addition. The latter should be used, as it involves less trouble in mixing. Ordinary BrunoHnum, used at full strength, penetrates through the dead bark and into the living cortex to a depth of a millimettg;* when appUed to the renewing bark three inches above the tapping cut. It penetrates through the stone cell layer, but in the trees examined it did not enter the layer in which the latex tubes are continuous. Half an inch above the cut the penetration was only 0-3 milli- metre, while at the cut it was increased only to 0-4 milli- metre and there was no well-marked sinus. Ordinary Brunolinum, 20 per cent. This mixture does not penetrate, except through the cracks in the dead bark, and there the penetration only amounts to 0-2 miUimetre into the living cortex. Ordinary Brunolinum, 5 per cent. No penetration was observed with this mixture. Brunohnum Plantarium, undiluted, penetrates through the dead bark scale and into the living cortex to a depth of 0-5 millimetre at a height of one inch above the cut. Where the bark layer has cracked and separated from the cortex, so that the liquid can collect behind it, the penetration may amount to 0-8 miUimetre. At the tapping cut the penetra- tion was 0-6 millimetre, with a well-defined sinus. Brunolinum Plantarium, 20 per cent. This mixture showed no penetration through the dead bark layer and no sinus at the cut. Brunolinum Plantarium, 5 per cent. This showed no penetration. Tests with "double strength" Brunolinum Plantarium did not show any marked difEerences in result from the preceding. Brunolinum and Brunolinum Plantarium are not recom- mended for application in undiluted form to Hevea bark except in special cases. For example, after scraping for Canker or Brown Bast, the application of the undiluted tt MISCELLANEA 255 liquid may be advantageous, as it will kill off a thin layer of the remaimng cortex and so destroy any diseased tissue which may have been left. But they should not be used undiluted for regularly repeated applications. The 20 per cent solution of Brunolinmn, or Brunolinum Plantarium, is used to cure Black Thread. It should be apphed to diseased trees as soon as the disease begins, and the application repeated every three days for six appheations. It is to be noted that this is a treatment to be adopted when the disease is active, i.e. when the decay is progressing and the wounds, or patches of diseased bark, are gradually growing larger. The 5 per cent solution of Brunolinum, or Brunolinima Plantarium, is used in preventive painting, i.e. to prevent" the attack of Black Thread. For that purpose it must be applied after every tapping during the rainy season. Carbolineum Plantarium Carbolineum Plantarium, undiluted, has a penetration similar to that of ordinary Brunolinum. At liree inches above the tapping cut it penetrated through the dead bark and into the cortex to a depth of 1-5 TnTllimetre. Lower down the penetration was less, but at the tapping cut it increased to a depth of 0-8 millimetre, and there was a well- defined sinus up to 5 millimetres broad. Carbolineum Plantarium, 20 per cent, showed no penetra- tion. The remarks on the uses of Brunolinum Plantarium apply equally to Carbolineum Plantarium. JODELITE The penetration of Jodelite, undiluted, is similar to that of ordinary Brunolinum. One inch above the cut the penetra- tion was 0-6 millimetre. It diminished below, but increased again at the cut to 0-5 millimetre, with a sinus 1-5 miHi- metre broad. No penetration was observed with the 20 per cent solution, except to a slight depth through the cracks in the dead bark layer, producing shallow furrows on the surface of the cortex. 256 THE RUBBER TREE Tliis substance can be used for the same purposes as Brunolinum. Agrisol {Soluble Solignum) Agrisol, applied undiluted, penetrated at tlie tapping cut to a depth of 0-6 millimetre ; its penetration is therefore equal to that of Brunolinum Plantarium. In 20 per cent solution it penetrated slightly deeper than 20 per cent BrunoHnum Plantarium, the depth being 0-3 millimetre for the former and 0-2 millimetre for the latter when tested at the same time. This substance can be used for the same purposes as Brunolinum Plantarium. IzAL A 20 per cent solution of Izal did not penetrate through the dead bark layer one inch above the cut, but at the cut it penetrated to a depth of 0-8 millimetre. The penetration of 20 per cent Izal at the cut is consequently as great as that of undiluted Carbolineum Plantarium, and it is not safe for continuous use. Solignum This has been used in 5 per cent and 20 per cent solution for Black Thread. , Solignum is also recommended for painting exposed] wood before tarring it ; this treatment is said to prevent the attacks of boring beetles. Jeyes' Fluid This has been used in 20 per cent solution to cure Black Thread. If employed for preventive painting it should not, be less than 10 per cent. Creoline is similar to Jeyes' Fluid ;* it has been used in 5 per cent solution for preventive painting." Peecentage Solutions 20 per cent = 1 gallon to 4 gallons of water. 10 per cent = l gallon to 9 gallons of water. 5 per cent = l gallon to 19 gallons of wate». 2^ per cent = 1 gallon to 39 gallons of water. IX MISCELLANEA 257 Brimolinum Plantarium, Carbolineum Plantarium, Agrisol, and Izal mix with water. Ordinary Brunolinmn, Jodelite, and Solignuni do not. In making solutions of the latter, 1 lb. of soft soap must be added for eacb gallon of the pre- servative. Lime-sulphur Solution Various recipes for preparing Lime-sulphur solution are in use, one of which is as f oUows : Slake 4 lbs. of quicklime and put it in an iron drum or boiler with about 6 gallons of water. The boiler should be capable of holding about 12 gallons and should be marked inside at the 10-gallon level. Boil the bme and water mixture, and when boiUng add 4J lbs. of sulphur gradually, stirring the mixture aU the time. When all the sulphur has been added, pour in boiling water to bring the level up to the 10- gallon mark, and boil for an hour longer, keeping the total volume at 10 gallons by adding boiling water. When cool this forms the stock solution. For spraying foliage it should be diluted to a strength of 2 lbs. of sulphur per 100 gallons, i.e. it should be diluted to 22j times its volume. Flowers of sulphur must be used in preparing this solution. If it is desired to keep the stock solution for some time it should be stored in fuU, air-tight vessels. Lime-sulphur solution must not be stored in copper vessels, nor used for spraying from copper sprayers. After being used with this solution aU sprayers should be thoroughly washed out and cleaned. • Bordeaux Mixtuhe Bordeaux mixture is made by mixing together a solution of copper sulphate and rnilk of lime. Different proportions have been recommended from time to time, but it is now usual to take equal quantities of lime and copjper sulphate. 5 lbs. of lime and 5 lbs. of copper sulphate in 50 gallons of water may be xised. This gives a nominal excess of lime, which is an advantage in countries where lime is generally very impure. The Tnillr of lime and the copper sulphate solution must be made separately and then mixed. It was formerly advised that each should be made up to 25 gallons before 258 THE RUBBER TREE °=^ mixing, and the two Ohen pouied simultaneously into a third receptacle, but according to the Wobiirn authorities that is unnecessary, and better results are obtained by pouring a strong copper solution into the milk of Ume. The amount of copper sulphate which will dissolve in water depends upon the temperature. Roughly, at 50° F., 100 parts of water will dissolve 36 parts of copper sulphate, while at 70° F. 100 parts of water dissolve 40 parts of copper sulphate. As a gallon of water weighs 10 lbs., 10 gallons of water wiU dissolve 36 lbs. of copper sulphate at 50° F,, and 40 lbs. at 70° F. But in making strong solutions allow- ance must be made for the lowest temperature to which the solution will be subjected, otherwise some of the copper sulphate will crystallise out as the solution cools. In practice it is not advisable to try to work too near the actual limits. If stock solutions of copper sulphate are made, they should not contain more than 2 or 2^ lbs. to the gallon. In preparing Bordeaux mixture, dissolve the 5 lbs. of copper sulphate in 5 gallons of water. The easiest way is to tie up the copper sulphate iu a piece of sacldng and sus- pend it at the top of a tub of water. The receptacle must not be made of iron or ziuc. This solution should- be begun the day before it is required. Put 5 lbs. of quicklime into a bucket, and slake it by sprinkling it with a little water and leaving it for about half-an-hour or so to crumble down. Then mix it with more water so as to form a cream or milk, and finally pour it into a tub, adding water to make the quantity up to 45 gallons. This may also be done the day before using ; the Ume water deteriorates slightly owing to the absorption of carbon dioxide from the air, but if the liquid is undisturbed this action is confined to a surface film. When required for use, stir up the 45 gallons of milk of lime, and pour into it the 5 gallons of copper sulphate solution, stirring it just enough to secure complete mixing. This final mixture must not be made in iron or zinc vessels ; a wooden receptacle is the best. Very little stirring is required after the final mixing. If the sprayers, are not provided with strainers, , the mixture must be poured into them through a strainer which will remove any particles of sand, etc., which might block K MISCELLANEA 259 the tubes. It must be remembered that the fungicidal substance is tbe bluisb-white precipitate which is suspended in the liquid, not the clear liquid which remains after the precipitate has settled. It is customary to give tests to determine whether all the copper has combined with the lime, or whether any copper remains in solution. With the quantity of Ume stated above, it is very improbable that any dissolved copper will be left. If, however, it is desired to test the mixture, the following method should be adopted. Put a few drops of a solution of potassium ferrocyanide into a white saucer with some water, and drop into this some of the clear liquid obtained after the Bordeaux mixture has been allowed to settle. If a brown or red coloration appears there is some copper left in solution. More Tini1> of lime must then be added to the Bordeaux mixture, and tiie test repeated. WoBUKN Bordeaux Recent researches at the Woburn Experimental Fruit Farm have led to the recommendation of the following modified Bordeaux mixture, knoAvn as Woburn Bordeaux. With this mixture much less copper is required, and clear Ume water is used instead of Tnifk of hme. The quantities required are 1 lb. of copper sulphate to 13^ gallons of clear lime water, with the addition of soft water sufficient to bring the whole to 76 gallons. Dissolve 1 lb. of copper sulphate, as directed above, in a gallon of water. Slake about a pound of quick- lime, and put it in a tub with about 30 gallons of water ; stir up the mixture two or three times and leave it to settle until the liquid becomes quite clear. The clear Uquid contains lime in solution and is lime water. Run ofi 13 J gallons of the clear lime water, and mix it with the copper sulphate, not in an iron vessel. Finally, add soft water to bring the whole mixture up to 76 gallons. As the lime in this preparation is reduced to the minimum, the liquid should be tested by the ferrocyanide method, and if the test shows that some copper stUl remains in solution more lime water must be added. The advantages of the Woburn Bordeaux are: (1) It 260 THE RUBBER TREE °^- ^ requires a smaller quantity of copper sulphate and is there- fore cheaper ; (2) lime water is used instead of milk of lime, and, with the poor quality of lime which alone is available in many districts, the former is more easily obtained in a satisfactory strength. If soft water is not procurable, hard water may be softened by adding Kme water to it. Water in a chalk district may be softened by adding about 26 fluid ounces of Ume water to every 10 gallons, and even in the case of soft water, or rain-water, 4 or 5 fluid ounces of lime water may with advantage he added to every 10 gallons to remove the carbon dioxide in it. This should be done before adding the water to the copper sulphate-lime water mixture. The preparation of these spray fluids is no doubt a trouble- some process, but it is within the capacity of the average dispenser. Attempts have been made to avoid all the trouble by manufacturing a paste which has merely, to be mixed with water before using, and these have been success- ful, as far as temperate countries are concerned. But these pastes invariably decompose under tropical conditions, and up to the present no method of overcoming that appears to have been discovered. CHAPTER X FUNGI ON HEVEA The following teclinical descriptions of tlie fungi which, have been referred to in connection with the diseases of Hevea are included here for convenience of reference. Hymenomycetae Marasmius equiarinis, Mull. — ^Pileus up to 8 mm. diameter, hemi- spherical, umbilicate, deeply radially sulcate, somewhat membranous, yellow-brown, red-brown, or. ochraceous, with a minute black umbo at the base of the umbilicus ; gills distant, five to eight, white then cream-coloured, broad, attenuated behind, united into a coUar round the stalk ; stalk black, shining, up to 2 cm. high, 0-25 mm. diameter, insititious, or arising from black, shining, rhizomorphic mycelium ; spores white, narrow-oval, inequilateral, or clavate, 10-14 xi (i. Fames lignosus, Klotzsch. — ^Woody, imbricated, sometimes per- ennial ; pileus dimidiate, usually about 10 x 6 cms., often larger, orbicular, at first red-brown with a yellow margin, becoming pale yellow-brown, with concentric red-brown lines, smooth, feebly sulcate, faintly radially striate and siUcy ; thickness (with two pore layers) 1-1-5 cm. ; pore surface at first orange, becoming red-brown ; pores minute, 0-06-0-12 mm. diameter, 2-5-3'5 mm. long ; context white, pores red-brown in section. Fames lamaoensis, Muxrill. — ^Applanate, rather thin, hard, frequently concentrically grooved, purple-brown, glabrous, with a hard outer crust ; internally yellow-brown, often with concentric growth zones, composed of two kinds of hyphae, the one thin-walled, the other thick- walled and resembling the setae. Pore surface dark brown or purple- brown ; pores minute ; setae numerous, obtuse. Fames pseudo-ferrms, Wakefield. — ^Pileus sessile, dimidiate, ungulate, or irregularly undulato-applanate, sometimes imbricate, glabrous, not zoned, with a rigid crust which cracks when dry, ferruginous becoming dark brown, the sterile margin whitish and swollen. Context floccose, cinnamon becoming brown. Tubes concolorous with the context, 261 262 THE RUBBER TREE whitish within. Pores minute, roimded, thick-walled, whitish, becoming yellow when bruised. Poria hypohrmnea. Fetch.— Effused, at first pale ochraceous, then pinMsh-red, becoming brownish-red, and finally slate-coloured ; margm at first white, tomentose. Basal layer blackish-brown, stout and compact when developed on a level surface, but loose and woolly when on an irregular surface or on soil, etc. Thickness of the compact form about 1-5 mm. Pores small, 0-1 mm. diameter. Cortidum salmonicolor, B. and Br.— Membranous, effused, rose- pink, or ochraceous, inseparable from the substratum, waxy when moist, finally cracked and areolated ; basidia clavate, tetrasporous ; sterigmata slender, 4-6 jn long ; spores pyriform, hyaline, apiculate, 9-12 X 6-7 /x. Gyphella Heveae, Massee. — Cups minute, 0-5 mm. diameter, scattered or gregarious, sessile, cup-shaped and expanded when moist, con- tracted and subglobose when dry, externally ininutely pulverulent, honey-coloured ; hymenium smooth, pinMsh-white ; spores elliptical, hyalme, 7-8 x 5 /u,. Phycomycetae Phytophthora Faberi, Maubl. — Mycelium richly branched, inter- and intracellular, aseptate in the early stages, becoming septate later. Sporangiophores sympodially branched, b'earing up to twenty sporangia or more. Sporangia ovate, or elongated ovate, 26-90 x 18-37 fj,, average 50 x 28 /i ; spherical resting conidia 23-50 fj, diameter. Phytophihora Meadii, McRae. — Mycelium branched, at first con- tinuous, then septate ; hyphae 3-6 to 10 fi diameter, inter- and intra- cellular. Sporangiophores branched, 10-200 /x long, but sometimes short ; sporangia obpyriform but variable, terminal or lateral, on the fruits 33-67 x 14-28 ju, in water 20-44 x 16-29 /x ; zoospores ovate or ellipsoid, biciUate, cilia 16-26 fj, long, spores globose, 7-10 fi ; oogonia pyriform, hyaline, smooth or rugose, on the fruits 20-48 x 20-40 /x, in culture 22-49 x 20-45 /x ; antheridia persistent, hyaline, circular or ovoid, smooth, 8-16 x 10-16 /x, surrounding the base of the oogonium and part of the oogoniophore ; oospores spherical, on the fruits 18-28 X 18-26 /x, in cultures 16-32 x 15-32 /x, wall 2-4 /x thick, yellow or yellow- brown, smooth. Pyee nom ycetae Meliola Heveae, Vincens. — ^Mycelium scanty, forming small patches about 2 mm. diameter, dichotomously branched, 7-9 jj, diameter, closely septate, constricted at the septa. Perithecia globose, up to 250 fi diameter, black ; asci elliptic, two-spored, 60-70 x 40-50 /x ; spores brown, narrow-oval, four-septate, constricted at the septa, 45-50 X 16-18 fj, ; setae brown, rigid, abruptly inflated at the base, 60-55 X 9-12 fx. On leaves of Hevea hrasiliensis. Para. FUNGI ON HEVEA 263 Cha^opeltopsis fcmiissiim (Petcli), Theiss. = .4s ^ . Additions to Ceylon fungL Annals, Royal Botamc Gardens, Peradeniya, vi. pp. 195-256 (1917). , , „ Sphaerdia Seveae, Aposphaeria Heveae, Ascochyta Heveae, etc 272 THE RUBBER TREE Hevea bark disease. Tropical Agriciilturist, 1. (1918), pp. 14-17. Brown Bast. The application of preservatives to renewing bark of rubber. Leaflet No. 9, Department of Agriculture, Ceylon (1918). Brown Bast. Leaflet No. .12, Department of Agriculture, Ceylon (1919). Brown Bast. Tropical Agriculturist, liii. (1919), pp. 133-138. Peteks. tJber eine Fruchtfaule von Hevea brasiliensis in Kamerun. Bericht ii. die Tatigkeit der Eais. Biolog. Anstalt f. Land- u. Forstwirtschaft im Jahre 1911. Mitt, aus der Kais. Biolog. Anstalt, etc., 1912, No. 12. Phytopkthora fruit rot. Pkatt, H. C. Preventive measures against Bla<:k Thread. Agricultural Bulletin, Federated Malay States, v. pp. 180-182 (1917) ; also itt Tropical Agricul- tiirist, xlviii. (1917), pp. 304-306. Apparent relation between height of tapping cut and Black Thread attacks. Tropical Agriciilturist, xUx. (1917), p. 7. Rauds, R. D. De bruine binnenbastziekte van Hevea brasiliensis. Archief voor de Rubbercultuur, iii. pp. 156-159 (1919). Rant, A. Uber die Djamoer Oepas Krankheit und liber das Corticium javanieum Zimm. Bulletin du Jardin Botaoaique de Buitenzore, Ser 2 No. 4, 1912. RiCHABDS, R. M. Diseases of the leaves and stem of Hevea brasiUensis in the Malay Peninsula. Agricultural Bulletin, Federated Malay States, v pp 307-317 (1917). Gloeosporium ; Pink disease ; Die-back ; Thread Bhght ; PhytopMhora sp. ; Burrs. Brown Bast and Black Thread. Circular No. 1, Malay Peninsula Agricultural Association, Myoological Department (1917). RirpDSfG, A. M. A. De resultaten van de voorgezette teerbehandeling op de gouvemements rubberondememing Kali Telo. Nederlandsch-Indisoh Rubbertijdschrift, April 10, 1918, pp. 63, 64. Use of tar as a preventative of Black Thread. RoEEB, J. B. The South American Hevea leaf disease. Bulletin of the Depart- ment of Agriculture, Trinidad and Tobago, xvi. pp. 128, 129 (1917). Fusicladium macrosporum in Trinidad. Rtjtgees, a. a. L. jffej«a-kanker. Meded. v. d. Afdeeling voor Plantenziekten No. 2 (1912). Waamemigen over Hevea-ha^ikeT U. Ziekten en Plagen van Hevea in de Federated Malay States. Meded. v.d. Afdeeling voor Plantenziekten, No. 4, (1913). Set)ea-kanker III. Meded. v.h. Laboratorium voor Plantenziekten No 28 (1917). ' Hevea-kankei. Archief voor de Rubbercultuur, Deel 1, No. 2, April 1917 Bliksemschade bij Hevea. Archief voor de Rubbercultuiu:, 3rd vear nn 163-171. •' ' ^^" Lightning injuries. Rtjtgees, A. A. L and Abens, P. Diseases of Hevea brasiliensis in Java Rubber Recueil (1914), pp. 130-139. Rtjtgees, A. A L., and Dammeeman, K. W. Ziekten en Besohadigineen van Heveabrasilvirms op Java. Meded. v.h. Laboratorium voor Pla^i^ekten, No. 10 (1914). ' Shaeplbs, a. The spotting of prepared plantation rubber. Bulletin No 19 Department of Agriculture, Federated Malay States (1914) ' Host plamts of Pink Disease in Malaya. Agricultural Bulletin, Federated Malay States, m. pp. 203, 204 (1915). Jjeueraiea Tephroaia Hookeriana ; Indigofera arreeta ; Clitoria cajanifolia. BIBLIOGRAPHY 273 Bittk scraping and bwk aflfeotions. Agricultural Bulletin, Federated Malay States, ui. pp. 420-426 (1915). Bordeaux mixtxire as a spray for rubber ti-ees. Agrioultuisvl Bulletin . Federated Malay States, iii. pp. 447. 448 (1915). Spottings in plantation rubber due to fungi. Transactions, Third Inter- national Congress of Tropical Agrioxilture, i. pp. 679-687 (1916). U^liiM eoaata on Hevea bmsilmms : preliminary note on further work. Agricultural Bulletin, Federated Malay States, iv. pp. 100-105 (1916). Scorched trees and tlieir treatment. Agricultural Bulletin. Federated Malay States. V. pp. 1, 2 (1916). U^uUna sonakt — a fungus affecting Heita brasUieiisis. Bulletin No. 25, Department of Agriculture. Federated Malay States (1916) ; also Annals of Applied Biol(^y, iv. pp. 153-17S (191S). Shsltos AuAB, W. B. Clean clearing, pests ivud diseases. Agriculturad Bulletin, Federated Malay States, v. pp. 299-306 (1917). General methods of treatment of diseases. StxHKOEK. K. L.. and Fol, J. 6. Die Zersetzung des Kautsohuks diurch Mikroben. Centralhl. f. Bakt., Abt 2. Bd. 40, pp. 87-98 (1914). SorTH. F. W. Notes on the distribution and field treatment of Fink Disease. Agricultursd Bulletin, Federated Malay States, iv. pp. 47-58 (1915). Buried coconut trunks and root diseases of rubber. Agricultural Bulletin. Ftederated Malay States, vi. p. 269 (191S). Black Thread. Malayan Tin and Rubber Journal, Jime 29, 1918. STAHKii, G. De 5ec*a-hladriekte van Zuid-Amerika. Meded. v.h. Dept. r. Landbouw in Suriname, Xo. 1 (1915). Over de bestnjding der Zuid-Ametikaansche £^«i«a-bladziekte. Paramaribo, 1916,-2 pp. Treatment of the Fiif^icladium leaf disease. De Zoid-AmerikaAnsolie Ifetvo-bladziekte. Department v.d. Landbouw in Suriname, BuUetin No. 34 (1917). Swart, X. L. Een en ander over Heveaziekten. Nederlaadsch-Indisch Rubber- tijdschrift, AprU 1. 1918, pp. 27-33. Diseases in West Java. VsRNST. G. Rapport de mission sur quelques maladies d'Hteea et iusectes nuisibles. Saigon, 1912. Aceount of Fames Kyuosus, Cortitdtim salmonicolor, Botryodij^odia Theobmmm in the Federated Malay States. ViscBJfs, P. Contribution 4 F6tude des maladies de VHrnva brasiliensis. Bulletin de la Soci^te de Pa^dogie v^tale, ii. (1915). Leaf and stem diseases in Bn^. PESTS Ardsn. S. Mites in rubber nurseries. Agricultural Bulletin, 8ti«its and Federated Malay States, iv. pp. 229, 230 (1905). Ar£n^ p. Een vocur Hevea sohadelijke oeret {Hohhidiia leueoph^alma, Wied.). Aarohief voor de Rubbercuttuur, Jahr. 3, No. 10 (1919). BAs^tARO, B. H. F. Damage caused by wild elephants to agricultural property. Agricidtund Bulletin, Federated Malay States, t. pp. 61-63 (1916). Bkkhakd, C Sur quelques maladies de Thaa assamica, de Kidaaa ehstica, et de Hetta bntsSuHsis. Bulletin du D6partemeut de FAgricuItuie aos Indes ntorlandaises, vi. (1907). Mites in Heita nurseries. Sur quelques maladies des plantes a oaoutohoua Bulletin dn D6partement de TAgriculture aux Indes n^rlandaises, sii. (1907). JkGtes on Hevea, T 274 THE RUBBER TREE Dammebman, K. W. De Hevea-termiet op Java. Meded. v.d. Afdeeling voor Plantenziekten, No. 3 (1913). Dammbrman, K. W., and Roefkb, W. Die tierisohen Feinde der Kautschuk ■ und Guttaperoha-Gtewaohse. Rubber Reoueil (1914), pp. 105-116. Geeen, E. E. Animals associated with the Hevea rubber plant in Ceylon. Circulars and Agricultural Journal of the Royal Botanic Gardens, Ceylon, vol. iv. No. 12 (1908). The rubber slug (Mariaella dussumieri. Gray). Circulars and Agricultural Journal, Royal Botanic Gardens, Ceylon, vol. v. No. 22 (1911). On some coccidae affecting rubber trees in Ceylon, with descriptions of new species. Journal of Economic Biology, vi. pp. 1-37 (1911). Stem and root borer of Hevea. BiiHetin No. 3, Department of Agriculture, Ceylon (1913). On some animal pests of the Hevea rubber tree. Transactions, Third Inter- national Congress of Tropical Agriculture, i. pp. 608-636 (1916). Haoendokn, M. Borkenkafer (Ipidae) welche tropiso^e Nutzpflanzen bescbadigen. Der Tropenpflanzer, vol. 17, pp. 157-160, 211, 212. Keuchenius, p. B. Een slakkenplaag in de Hevea. Meded. v.h. Besoekisch Proefstation, No. 10 (1914), pp. 7-9. Pratt, H. C. Notes on Termes gestroi and other species of Termites found on rubber estates in the Federated Mala,y States. Bulletin No. 1, Department of Agriculture, Federated Malay States (1909). Observations on Termes gestroi as affecting the Para rubber tree, aryi methods to be employed against its ravages. Bulletin No. 3, Department of Agricul- ture, Federated Malay States (1909). Termes gestroi as a pest of the Para rubber tree. Transactions, Third International Congress of Tropical Agriculture, i. pp. 637-640 (1916). RiOHAiiDS, P. B. A note on the sulphur-arsenic mixtures for fumigating Termes gestroi. Agricultural Bulletin, Federated Malay States, iii. pp. 225-229 (1915). The history and present position of white ant treatment in Malaya. Agricul- tural Bulletin, Federated Malay States, v. pp. 338-348 (1917). Notes on Entomology in the Federated Malay States during 1917. Agricul- tural Bulletin, Federated Malay States, vi. pp. 411-414 (1918). INDEX Abnormal le&f-fall, 88, 100, 105 ActaMopsyche sHtikni, 236 AeUoomyces dastica, 216 Actinomyces fitscus, 216 Ahdia palembanica, 3o iL^Jsol, 256 JMzzia, 13, 45, 62, 151 Anatto, 135 Antelopes, 223 Ants, 241 wMte,225 Aposphaaia Htveae, 73 Apos^aeiia Vlei, 83 Arrowroot, 68 Aiseuite of soda, 239 Ariocarpus inte^foUa, 35, 45, 68 Asc^sonitt, 95 AscoAyta Seveae, 84 Ascoc^)ta rim blight, 84 AUerolecanium pustnUms, 240 Avlardes mUUaris, 238 Bacterium pndigiosum, 210 Bag worms, 236 Buts, poisoned, 240, 245 Bamboo, 35, 40, 243 Bandicoots, 224 Badc-eating caterpillars, 235 Bark rot, 119 Batoeaa Tvbus, 230 Benzene-resin sdution, 126 Berrya ammonina, 35, 55 Bird's-eye spot, 81 Black line canker, 119 Black lines in wood, 58 Black patches in wood, 200 Black scrap, 218 Black spots on rubber, 210 Black Stripe, 119 Black Thread, 119 Blue-black spot on crepe, 211 Bois Immortelle, 35 Bombas, 35 Bordeaux mixture, effect on rubber, for Fink disease, 140 preparation of, 257 Boring beetles, 232 221 Botryodiphdia Tlteobromae, Die-back, 148 on crepe, 211 root disease, 71 Brachytrupes achaiiHus, 246 Branches, death of, after thinning, 6 Breadfruit, 45 Brown Bast, 169 Brownea grandiceps, 45 Brown Boot disease, 41 Bnmfelsia americana, 45 Bmnolinnm, 254 efiect on scrap, 124 Burrs, 180 Cacao, 35, 45, 135, 151 among rubber, 10, 36, 46, 62, 114, 117 Cacao canker, 114, 117, 131, 233 Cacao pod disease, 114 Cambium rot, 119 Camphor, 35, 45, 135, 155 Canker, 111, 205, 233 CaraTonica cotton, 45 Carbolineum Plantarium, 255 Case worms, 236 Cassava, 35 Cassia javanica, 55 CasHOoa, 45, 135, 151 Catatauma Hubert, 83 Caterpillars, bark-eating, 235 swarming, 245 Cattle, 223 Cavities, treatment of, 19, 26 Ceara rubber, 13, 35, 45 Ciphalatros, 88 CepAoIosporium Leeanii, 241 Chaetopdtopsis tenuisHma, 95 Change-over tapping, 128 Chinosol, 180, 214 Chrmnosporium cmstaceum, 211 Cinchona, 135 Cinnamon, 135, 242 Ciimamonatm Cassia, 45 Claiet-coloured canker. 111 Clean clearing, 4 Cleaning-up forks, 20 aose planting, 5, 12S Cockchafer grubs, 24 275 276 THE RUBBER TREE Coconut, 35 Oodiaeum variegatum, 45 Co£Fee, 35, 45, 135, 243 among rubber, 11 Collar rot, 56 OoUetotrichum Heveae, 86 Oolocaaia, 131 Coloured latex and scrap, 218 Coloured spots on rubber, 208 Gomocritis pieria, 235 Copper and rubber, 218 Cork warts, 195 Gorticium caiceum, 134 Gorticium javanicum, 134 Gorticium lilacinofuscum, 135 Gorticium Zimmermanni, 135 Cover-plants, 9 Cowdung and cla.y, 15 Crickets, 245 Grotalaria fulva, 12, 55 Crotalaria striata, 11, 135 Croton, 45 Gyphdla Heveae, 156 Gyrtacgmthacris nigricornis, 239 Dadap, 13, 35, 37, 45. 67, 68, 135, 151 Dark blue spots, 211 Decay of renewing bark, 119 Deer, 223 Dendrocdlamtcs, 35, 40 Derris, 35, 55, 69 Die-back, Botryodiphdia, 148 Phytophthora, 106 Diplodia cacaoicola, 151 Diplodia rapax, 151 Disinfection of tapping knives, 129, 154 Distances, planting, 7 Djamoer oepas, 135 Dothidella Ulei, 81 Durian, 135 -Dry root and collar rot, 58 Dry rubber, spotting of, 214 Ebony, 55 Elephants, 223 Eriodend/ron, 11, 46 Erythrina, 13, 35, 37, 45, 67, 68, 135, 151 Erythroxylon Coca, 45, 135 Eugenia, 57 Euphorbia hirta, 93 Euphorbia Rothiana, 93 EutermAs inanis, 225 Examination of roots, 25 Exudations of latex, 204 Fasciation, 188 mcua, 35, 39, 151, 205, 243 KUing cavities, 18, 26 Fires, 200 Flush, red, on sheet, 213 violet, on sheet, 213 yellow, on sheet, 213 I'om,ea lamaoensis, 41 Fomes lignomis, 27 hosts of, 35 Fom^s pseudo-ferreus, 50 Forking, 17 Forks, cleaning up, 20 Formalin for prevention of spots, 214 Formalin sodium bisulphite, 124 Fruit disease, Oloeosporium, 89 Phytophthora, 100, 103 Fusarium Heveae, 83 Fusicladium macrosporum, 78 Fusicladium stem disease, 153 Globular shoots, 188 Gloeoaporvum alhorubrum, leaf disease, 89, 90 fruit disease, 89 stem disease, 146 Gloeoeporium elasticae, 90 Gheosporium Heveae, 90 Goats, 223 Greasiness of sheets, 217 Green manure plants, 11 Green twigs, death of, 145 Grevittea, 13, 45, 62, 135 Grey bUght, 86 Grooming, 16 Guignardia Heveae, 85 Guignardia rim blight, 85 HalmiUa, 35, 55 Heart rot, 23 Helminthosporium Heveae, 81 Hibiscus, 56 Holotrichia leucophihalma, 243 Horse-hair blight, 160 Horses, 223 Hura crepitans, 45 Hymenochaete noxia, 48 HypocreUa Beineckiana, 96, 241 Indeterminate leaf spots, 86 Intercrops, 9 Izal, 256 Jak, 25, 35, 45, 68, 135 Jatropha Curcas, 94, 131 Jeyes' Fluid, 164, 256 Jodelite, 255 Jungle stumps, 2, 35 Kapok, 136 Kapok stumps, 11, 46 Knobbed trees, 196 Kola, 136 Koompassia malaccensis, 35 Kreizschmaria miisropus, 144 Kumpus, 35 Lasiodiplodia Theobromae, 151 Lateral roots, wounds on, 72 Latex, exudations of, 204 Latex tubes, formation of; 175 INDEX 277 Leaf diseases, general, 77 summary of, 96 Leaf -fall, abnormal, 88, 100, 105 climatic, 91 Oheosporium, 89 PhytopMhora, 100, 105 Leaf pits, 200 Leaf spots, indeterminate, 86 Lecanium nigrum, 240 Lecanium viride, 240 Lepidiota pinguis, 242 Lightning, 201 Lime and fungi, 24 Lime (citrus), 135 Lime-sulphur solution, 257 Liming for root disease, 24 Liquid fuel and tar, 125, 252 Livistonia cochin-chinensis, 35 Locusts, 238 Loranthus, 164 Lunumidella, 55, 62 Maorophoma vestita, 151 Malformed stems, 196 Mango, 135, 151 Manihiot dichotoma, 205 Manihot piauhyensis, 205 Maranta arundinacea, 68 Marasmius equicrinis, 160 Mariaella duasumieri, 246 Megalonectria pseudotrichia, 67 Melanopsarmnopsis Heveae, 81 Melia dubia, 56 Meranti, 35 Merbau, 35 Mesua fetrea, 45 Mildew, 91 Mites, 237 Moechotypa verrucicolUs, 243 Monaacits heterosporus, 210 Moulds on rubber, 219 Mouldy rot, 153 Mycogone sp., 213 Na, 45 Necator decretus, 136 Nibong, 35 Nodules, 172, 180 on leaves, 95 Nurseries, care of, 163 Nursery plants, leaf injuries, 87 Nutmeg, 131, 135 Oecophylla smaragdina, 241 Oerets, 243 Oidium sp., 93 Oncosperma filamentosa, 35 Opaque spots on sheet, 212 Orange, 135 Pachytylus sp., 239 Panax, 55 Papaw, 68, 161 Paraffin wax, 126 Paris green, 246 Parmarion reticiilatus, 246 Parodiella perisporioides, 11 Passalora Heveae, 81 Patch canker, 111 PeniciUium maculans, 213 Pepper, 135 Percentage solutions, 257 Permanganate of potash, 219, 221 Pestahzzia palmarum on leaves, 86 on stems, 163 PhyUanth/us Nwwri, 94 PTvyllanthas reticulatus, 94 Phylloaticta Heveae, 86, 87 PJiyllosticta ramicola, 146 PkytopMJiora diseases, 100 summary, 132 Phytophthora Faberi, 131 Phytophthora Meadii, 131 Phytophthora, species of, on Hevea, 131 Pigs, 223 Pink disease, 134, 205 Planting distances, 7 Pod disease, Oheosporium, 89 Phytophthora, 100, 103 Poisoned baits, 240, 245 Polyporus rugulosus, 72 Polyporus zonaUs, 33 Porcupines, 223 Poria h/ypobrunnea, 52 Poria hypolateritia, 50 Preservatives, action of, on renewing bark, 249 Protection of wounds, 15 Pruning, 13 Psyche snelleni, 236 Pumelo, 55 Purple canker. 111 Ramie, 135 Red flush on sheet, 213 Red root disease, 52 Red rust, 88 Red spots on rubber, 210 Renewing bark, action of preservatives on, 249 Resin-benzene solution, 126 Resin-wax mixture, 126 Rhinoceros beetles, 244 Rim blights, 83 Rodents, 224 Root and stem borer, 230 Root diseases, diagnosis of, 27 effect on latex flow, 22 general efiect of, 21 general treatment, 24 summary of, 74 Rubber, dry, spotting of, 214 effect of spotting, 215 Rubber logs, 7, 54, 62 Rubber pads, 121, 127, 206 Rust on sheet rubber, 217 278 THE RUBBER TREE "Sakit Mtam," 43 Scale insects, 94, 96, 240 Scolecotrichum Heveae, 83 Seolopia, 55 Scorched trees, 199, 233 Scraping, 16 Scraping for Brown Bast, 177 SeeoUiiigs, stem disease of, 163 twisted, 191 Serdang, 35 Shorea sp., 35 Shot-hole leaf disease, 82 Slugs, 246 Sodium bisulphite, 213 Soft soap, 257 Solignum, 256 Sooty moulds, 94 South American leaf disease, 78 Sphaerella Crotala/riae, 11 SphaereUa Heveae, 85 Sphaerella rim blight, 85 Sphaeronema, 153 Sphaerostilbe repens, 64 Spodoptera sp., 245 . Spondylocladium maculans, 211 Spots, black, 210 blue-black on crepe, 211 dark blue, 211 on rubber, 208 opaque, on sheet, 213 prevention of, 213 red, 210 . traUsparent, 212 Spotting, effect of, on rubber, 215 of dry rubber, 214 Spraying for leaf disease, 78 Stem disease of seedlings, 163 Stem diseases, summary of, 165 Stem, twisted, 197 Stems, malformed, 196 Sterilisation of soil, 164 Stilbum oinnabarinum, 67 Stilbum nanum, 67 Stockholm tar, 15, 224 Stripe canker, 119 Stripping, 177 Strobilanthes, 135 Stump extraction, 4 Stumps, Albizda, 13, 62 Cacao, 10, 13, 33, 46, 62 Hevea, 13, 33, 62, 232 jungle, 2 root disease of, 71 Tea, 11, 13, 33, 62 Sugar-cane, 151 Swarming caterpillars, 245 Tacky rubber, 218 Tallow and tar, 125, 252 Tapping knives, disinfection of, 129, 154 Tar, 125, 251 and Brown Bast, 179 and Uquid fuel, 125, 252 and Pink disease, 140 and taUow, 125, 252 on canker, 116 on wounds, 15 Tea, 35, 41, 55, 135, 151, 158, 160, 242 in Bubber, 11, 36, 62 Tephrosia Candida, 12, 55 Termea gestroi, 226 Termes obscuriceps, 225 Termea redemanni, 225 Termites, 225 Thespesia populnea, 45 Thinning out, 5, 36, 54, 62 Thread bHght, 155 Thyridaria tarda, 151 Tobacco, 131 Top canker, 160 Transparent spots on sheet, 212 Tree surgery, 18 Trenching for root disease, 24 Trichoderma Koningi, 211 Tricholepis lactea, 242 Twigs, green, death of, 145 Twisted seedlings, 191 Twisted stem, 197 UstuHma zonaia (root disease), 55 XJstulina zonaia (stem disease), 142, 205 Vaporite, 242 Violet flush on sheet, 213 Water-logged bark, 169 Wax on renewing bark, 126, 179 Wax-resin mixture, 126 Wet rot, 22 of Bevea roots, 50 White ants, 225 White lead paint, 15 White stem blight, 158 Wobum Bordeaux, 259 Wounds on lateral roots, 72 treatment of, 15 Xyleborus parvulus, 233 Xyleborus perforans, 233 Xylotropes sp., 244 Yellow flush on sheet, 213 Yellow latex, 218 Zygosporium paraenae, 83 Printed by R. & R. 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