CORNELL UNIVERSITY LIBRARY FROM Cornell University Library QK 725.M69 1852 PrIncI of the anatomy and Dhyflg 3 1 i 924 024 759 346 olin PEOCIPLES OF THE ANATOMY AND PHYSIOLOaT OF THE YEGETABLE CELL. BY HUGO YON MOHL, DOCTOU OF PHILOSOl^HY, MEDICINE, ANB feURGEUY; KNIfSITT OF Tim 0R1>ER OP THE WUlirEMBURGH CliOWN" ; ORDINAIIY PROCESSOR OF BOTANY IN THE UNIVKU&TTY OP TUBINGEN J CORREfePONT>IN« MEMBER OF THE DUTCH INSTITUTE ; 03^ THE AOADEMT OF SOIFN( E> OF STOCKHOLM; MEMBER OF THE IMPBRIAL LEOrOLD-CAROI;. ACADEMY OF NATURALISTS ; ("ORHESrONDlNC^ MEMBER OF TUB INSTITUTE OF FRANCE: OF THE ACAPEMIES OF SCIENCES OF BERLIN, MUNICH, TURIN, AND VIENNA. TRANSLATED (With the Aiithor''^ per7}US'iion) BY L^efiirer on Bofmijf at St, Georges JfoqnUd; AM or of Outlines of Anafomical and Pli'l/shhffkai Bofanij ; I^mimmits of Botany; etc, etc. it!): m. MmXx^ikz Plate anti numerous OToatrcuts. LONDON: JOHN YAN VOOKST, PATERNOSTER ROW, MDOCaiJI. LOITBOH T E Mrtoait, PmNTER, 63, Snow Hilt AUTHOR'S PREFACE 10 THE ENGLISH TEAKSLATIOK Me. Arthur Henfrey having informed me ttat lie intends publishing an English translation of the pre- sent treatise, I take this opportunity of making known to the English reader the purpose I had in yiew in the preparation of the book. The following pages were not originally intended to appear as an independent work, or to give a summary of the wide subject of the Anatomy and Physiology of Plants, but appeared as an article, in the ^^ Cyclopaedia of Physiology" published by Dr. Rudolph "Wagner, of Gottingen, drawn up to furnish students of Animal Physiology, and more particularly the Medical Profession, with a review of the Anatomical and Physiological conditions of Vege- tables (of the Cell), in order to enable them to form a definite judgment upon the analogies which might be drawn between the structure and vital functions of animals and plants. This intention, together with the circumstance, that I was compelled to crowd the whole exposition into the space of a few sheets, rendered it necessary to direct especial attention to the individual cell, as the fundamental organ of the Vegetable Orga- nism. Since, however, the cell only presents itself in anatomical and physiological independence in the lowest IV PREFACE. l>laiitS; and sincC;, in the more highly organized plants, both the structure and the physiological functions of tlie individual cells become subject to greater depend- once upon the other parts of the plant, in proportion as the collective organization of the vegetable is more complex ; moreover, since functions then present them- selves, of which no trace can be found in the lower plants, it became requisite to take account of the plants of higher rank, and of the various organs which these possess. The treatise, therefore, contains, if an imper- fect, still in many respects, a more extensive resttmS of Vegetable Physiology, than might be conjectured from the title. Unhappily, the Physiology of Plants is a science which yet lies in its earliest infancy. Few of its dog- mas can be regarded as settled beyond doubt ; at every step we meet with imperfect observations, and con- sequently with the most contradictory views ; thus, for example, opinions are still quite divided regarding the doctrines of the development of the cell, of the origin of the embryo, and of the existence of an im- pregnation in the higher Cryptogams. Both in these and in other cases, the small compass of the present treatise forbids a more extensive detail of the researches upon which the opposing views are founded ; I hope, however, that I have succeeded in making clearly pro- minent, the chief points upon which these contests turn, and thus, in facilitating the formation of a judgment by the reader ; and, I have never neglected to indicate the literature from which furt.her instruction is to be derived. TiruiHCxEJs^, Odobor VJlhj 1851, CONTENTS. iitiXKluciory Remarks ... . . 1 I — The Anatomical Condition of tlie Cell . . 2 A. Form of Cells . . . . > ib. B, Size of tlie Cell .... 8 C The Cell-membrane ... .9 a. Physical Properties ... ib. h. Structure . . . .10 c. Chemical Conditions ... 24 D. Cells in their E-eciprocal connexion . , 30 E. Contents of Cells . . , . 36 a. Primordial Utricle, Protopkbm, and Nucleus ih, b. Cell-sap ..... 40 c. Granular Structures . . . .41 cl Compounds dissolved in the Cell-sap . 47 F. Origin of the Cell . . . .49 a. Division of the Cell , . 50 b. Free Cell-formation . . . .57 1 L — The Physiological Conditions of the Cell . . 61 A. The Cell as an Organ of Nutrition . . 65 a. Absorption of Watery fluids . . iK b. Diffusion of the Sap in the Plant 70 e. Nutrient Matters . . . . 77 d Elaboration of the Nutriment . . 88 e. Secretions . . . . 93 / Evolution of Heat . . . .101 f> The Cell as an Organ of Propagation . 104 a. The Multiplication of Plants by Division . ik k Piopagation by Spores and Seeds , 110 a. Propagation by Spores . . .111 * Propagation of Thallophyi^es . ih. Propagation of the Cryptogams ) ^^^j having Stems and Leave J b. Propagation by Seeds . . 125 ' The Pollen . . .127 « The Ovule ... 129 ' / The Origin of the Embryo . 131 C The Cell as an Oi'gan of Motion . . 139 •55-% AKATOMY 8c PHYSIOLOGY OF THE VEGETABLE CELT 9i> a'O. ■S5 iaL., ., i-MwC— 3*^-'-'^t. SSTVj^'^Jj. ^ tm W\ II ,M^i. ^ y ^ 4 4 •■*' ""N ^U ,-^. J *^ I .:-s &■ f'yi J- ' "^v./ ^ i:? ■A- 2 I I 4 8 / i# / .- ..."-' ""'N JlO %f \ ^1?/ ^/ /.-■■"■•'"■--J w r * it i!c-5 P Ir. % Z4r a£^. ANATOMY AND PHYSIOLOGY OF THE VEGETABLE CELL. INTEODUCTOEY EEMAEKS. If we examine the texture of plants with a powerful microscope, we find that it does not consist, as appears to the naked eye or under slight magnifying power, of a homogeneous substance per- forated by a greater or less abundance of cavities, but is composed of minute portions, of definite form and organization, separable from each other (the elementary organs). Observ. Universal as the agreement among pliytotomists has been for some thirty or forty years on this fundamental proposition of vegetable anatomy, it was a long time before it acquired general recognition. The very founders of the anatomy of plants, Leeuwenhoek, Malpighi, and Grew, were, indeed, led by their researches to the detection and distinc- tion of the elementary organs as organized parts, but the real conditions were again misconceived throughout the whole of the eighteenth century. On the one hand, Ludwig and Bdhmer, seeking an analogy with animal cellular tissue, described vegetable cellular tissue as a mass of irregular fibres and lamellae interwoven together ; on the other hand, C. P. Wolff (theoria gemratlonisj described vegetable substance as a homogeneous mass hollowed into holes and canals, a view which still found an active defender durmg the first ten years of the present century, in Brisseau de Mirbel, and is even now held by him to be the condition in the earliest stage of development of vegetable tissue, if not that of the subsequent stages. More correct views were first substantiated by German pliytoto- mists of the present century. The primary form of the elementary organ of plants is that of a completely closed, globular, or elongated vesicle, composed of a solid membrane, and containing a fluid (utricle, utriculusj. If this remains still closed after its development is completed, it is called a cell, cellula ; but if a row of utricles arranged in a line become combined, during the course of their development, into a tube with an uninterrupted cavity, through the absorption of their cross walls, a compound elementary organ is produced, — ^the vessel (spiroid of Link), Ohserv. The tracing back of the whole of the elementary organs to the primary form of the utricle, has been accompHshed only quite recently. The earlier phytotomists, who took the elongated cells for long tubes, overlooked their analogy with the short cells, believing that they were rather to be compared with the vessels, and they described them as a special anatomical system under different denominations (fibres, lympha- tic vessels, &c.), in which error they were followed even by Treviranus B 2 ANATOMY AND PHYSIOLOGT OF (" Physioloy.''' i. 64), altliongb Sprengel, Ruclolphi, Link, and Kieser had already recognized that they all were modifications of the cell. Far less than this was the true nature of the vessels perceived hj the earlier phy- totomists j and I believe that I was the first to detect their origm from rows of closed cells [^^ Memoirs of the Acad, of Munich^' i. 445. De struc- tura imlmcwum, § 26 — 39). ISTo sharply defined line can be drawn be- tween vessels and cells, for reasons which will be hereafter discussed. Whether the milk-vessels^ which indeed occur only in a comparatively small portion of plants, and play a very subordinate part both in ana- tomical and physiological relations, originate in an analogous manner from rows of cells, or are to be regarded as a system essentially cliiferent from the rest of the elementary organs, is a question upon which no opinion has yet acquired an universal acceptance. Unger asserts the former (^^ Annals of the Vienna Museum^' ii 11) ; but it is more than doubtful whether his observations were accurate, and it seems that the milk- vessels ought to be regarded as membranous Imings of passages wliich appear be- tween the cells. {See an anonymous memoir in the ^^Botanische Zeitumj^'' 1846, 833, entitled "The Millc- vessels : thek Origin, t&c") The basis of the substance of all vegetables consists of tlie cells, since even in the most highly developed plants all the organs are in the youngest condition com|)osed of cells alone, and the vessels only appear during the subsequent development. In the lower plants (Fungi, Algse, Lichens, Liver-mosses and Mosses) all the elementary organs persist in the organization of the cell. Ohserv. The circumstances, that a plant is composed of cells alone, or also possesses vessels, have not that importance either in a systematic or a pLysiological pohit of view wliich De CandoUe attributed to them, when he used them for the piimary division of tbe vegetable kingdom^ into Cellular and Vascular plants, for these condition^) do not run parallel with the total organization of plants, since there exist both Cryptogamic and Phanero- gamic plants with and without vessels. I THE ANATOMICAL CONDITION OF THE CELL. A. POKM OF CELLS. The forms under which cells present themselves are so manifold, that a special examination of all would occupy a far greater space than can be devoted to it in this place ; I therefore confine my- self to a few observations. In the first place, in examining the form of the cell, we have to take notice that it depends upon two circumstances. On one hand the form of the cells is determined, like that of every organic body, by its indwelling laws of development ; on the other hand, the individual cell, in the fixr greater majority of cases, cannot follow those laws uninterruptedly, because it forms part of a com- pound tissue, and is compelled by its intimate connexion with the surrounding elementary organs, to accommodate itself to the space thus determined for it, and in consequence of the pressure to which it is exposed laterally from the surrounding elementary THE TEGETxlBLE CELL. 3 organs, to er-cell of Cooos hotryophora,. THE VEGETABLE CELL. 5 (fig 8) are, as a rule, distinguished from the short parenchymatous ceils, not only by their elongated, often fibrous shape, but also by the two ends being attenuated to points. In this case they are not arranged end to end in lines, but their attenuated extremities are interposed between the lateral surfaces of the cells situated above and below them; while the parenchyma cells, if, as is usual, they are arranged in lines, stand one upon another with flattened ends, their cavities being thus separated by partitions directed at right angles to their longitudinal axes. Link founded upon this differ- ence of the ends the distinction between parenchymatous and pro- senchymatous cells, a distinction which is indeed well grounded when we compare extreme forms, but which is by no means to be carried through, since the most manifold transitions occur from parenchymatous cells, with more or less oblique cross-walls, to perfect prosenchymatous cells. In many Thallophytes, especially in many^Fungi (e. g., Boletus iijniarms) and Lichens (e, g., in Evernia), isolated portions of the substance are found of fibre-shaped, frequently irregularly interwoven cells (IrregalaT cellular tissue of Kieser). Gradual transitions also occur from tliis form of cell to the form of the parenchymatous cell. The form of the parenchymatous cells is most intimately con- nected with theii' relative position. The simplest condition is afforded by such cells as lie one above another in a simple row, as the cells of the Oonfervce (pi. 1, fig. 1), articulated hairs, &;c. Here the cells become flattened on the sur- faces of contact, while the side-walls retain their natural curvature. Accordingly as these possess a cylindrical curvature, or one more approximating to a globe, does the entii^e cellular filament obtain a cylindrical or beaded shape. When parenchymatous cells lie side by side in a p. ^ simple layer, as is the case in the leaves of most Mosses and JungeomiannlcB^ and in the epidermis of the higher plants, their lateral surfaces, by which they are cohe- rent together, become flattened; while the lower and upper free sides are either more or less convex, coni- cally elongated (fio*. i), or quite flattened like the rest Ceiisofthe rn 1 ^ 111 n i n 'x j.1 j? i* epidennis of the Taken as a whole, such cells exhibit tlie lorm ol many- petal of angled plates or prisms, the shapes of which again pre- "^^'^'j^''^.^^*'" bent modifications, accordingly as the growth of the cells in the direction of the surface, which they combine to form, is uniform or irregular. The lateral faces of tabular cells are usually perfectly flat. Yet it sometimes happens, for instance in the anthers of Ghara^ and in the epidermal cells of many leaves (fig. 5), that the side-walls are curved into waving lines, or jzig- jgaggecl in sharp angles. It is not so easy to define the form of the parenchymatous cells when they are collected together in masses (fig. 6)^ as is the rule () A^STATOMY AND PHYSIOLOGY OF in the internal Mib&tance of organs, for instance in pith, in bark, &c., for here every cell is surrounded on all sides by other cells, and exhibits as many flattened surfaces as there are cells standing in connexion with it. Kie&er (^^Grundz, cler AQiatorroic der Pjimi- zen/' § 127) sought to demonstrate, that the form of the cell must necessarily be that of a rhombic dodccaheclrou under such circum- stances, since this form encloses the greatest space within the smallest amount of limits, and that their form is usually that of a ihombric dodecahedron elongated in a perpendicular direction, be- cause the primary form of the vegetable cell is not the sphere but the ellipsoid. This proposition may be admitted theoretically, but it would be a vain labour to seek actually to observe the form of the rhombic dodecahedron in a cell in nature, since the contigu- ous cells are ahvays far too unequal in size for them to become Fifj, 5 Fig 6 // 5 J A J Epilcnins of tlio lowei face of the leaf of lleUohoni&J-a^iidus PAroncliYinxtous cell«t from tho bark of Jbtijjhoi but caiim Mibih. moulded into regular mathematical forms by their reciprocal pres- sure. So that in cross sections of a parenchymatous tissue the cells very able number of sides (usually from iive to eight). It is therefore more suitable to call such cells polyhedral instead of dodecahedral On the more or less crowded ariangement of the cells it depends whether the plane surfaces of these meet at acute angles (fig. 7) ; or whethei*, when the cells are more loosely aggregated, the sur- faces of contact are but small (fig. 6), and large portions of the cell-walls between them remain unconnected with the neighbour- ing cells. In the latter case, the free portions of the cells retain their natural rounded form. In particular eases, however, the portion of the cell-wall immediately surrounding a plane surface in contact with another cell, glows out in a tubular form, so that THE VEGETABLE CELL Tvliea several such processes are formed, tlie cell acquires a stai'-like appearance. When in such cases the cells are arranged in one plane, as occurs in the cross-wallb of the aii-canals of many water- plants, all the rays of the star lie in one plane (figs. 8, 9) ; when, on the other hand, the cells are heaped together in masses, as in the pith of Jwneus efficsus, the rays project from all sides of the cell. r^r; 7. Cells of the pith of Acanthuh mollis Far more jErequent than such re- gularly branched cells, are those of a roundish form, exhibiting a shorter projection at one or more points, and so having a moder- ately irregular form ; the paren- chyma of the lower side of the leaves of most plants is com- posed of such cells (fig. 10). r,f/ 8. Stdlaic cellular tissue ftom the leaf s»tvlk of Ahi6a. V-TniJ ^.1 c-«« Partition "boundrng an air-canal m the loaf-stalk ot Bagittana sagittifoha. Fig. 10. •\ -0 \ rf^'k k^O >pi ParenclijTiiato^i's cells fi'om the leaf of Orehts mmcula* Ohserv, Some pliytotomi&ts have distinguished a greater immber of tissues according to the forms of the cellb, applying partictdar names to 8 ANATOMY AND PnYSIOLOGY OF tliem, especially Hayne {^' FIoqxo''' 1827, ii. QOl^Mejen ('' Fhytotomie'' 57, " Phjsiologie'' i, 12), and Morren {^^ Bulletin de VAcad deJBruxelles" V, J!^o, 3). The arrangement of Hayne, wMcli did not attract tlie least notice, I may pass over here. Mey en distinguished: \, Mere^icliyma — tissue composed of spherical cells, the cells only i^artially in contact ; 2, Parenchyma; 3, Frosenchyma — ^this name was applied by Meyen to the woody tissue of the Coniferse ; 4, Fleurenchyma, which was the name by which he distin- guibhed the prosenchyma of all other plants. The division of merenchyma from parenchyma was superfluous, and cannot be carried out, because there are so many transitional forms ; the alteration of the established term prosenchyma into pleurenchyma was altogether inconvenient, and was not adopted. But the wilderness of botanical terminology would have been increased beyond all reasonable measure by Morren, had not his subdivi- sions been passed over unregarded ; for he divided the parench3?Tna alone into no IckSs than eight tissues, which he named, merenchyma^ conenchyma, onenchyma, atractenchyma, cylindrenchyma, colpenchyma, cladenchyma, and j9r'i*s?>^e^^c/My??^o^. AH such far-fetched subdivisions of the cellular tissue are wholly valueless, because no exact connexion exists between form and function, and frequently enough the same organ is formed of cells differing considerably in form, — ^in two closely allied plants. B. SIZE OF THE CELL. Important as the accurate determination of the size of the indi- vidual elementary organ is, in many special researches, particularly those relating to the history of development, yet in general the knowledge of the size of cells is of very subordinate value ; and this the more that not only do the cells of the same organ exhibit extraordinarily great variations in respect to their size, but the contiguous cells of one and the same organ not unfrequently differ considerably from each other. Pollen grains afford a very striking example of the former ; their dimensions are tolerably constant in each species of plant ; but their diameter varies from 1-3 00th of a line in Myosoiis to 1-1 5th of aline and more in Ciicurbita, Sire- litcia, (ic. The cells of a single organ often dijBfer to the extent of some being twice or thrice as large as others. The diameter of the cells of parenchyma may be stated at a general average of from l-20th to 1-lOOth of a line ; but in paiti- cular cases (e. g , in the spores of many Fungi, in the yeast cells) it fells to less than l-500th, and in other instances it rises, 6. ^., in succulent parts, in the pith of the elder, &c,, to 1-1 0th of a line and more ; so that in such cases the individual cells are actually visible to the naked eye, which is not generally the case. The dimensions of many elongated cells form a striking contrast with this small magnitude of the majority of parenchymatous cells, since while the transverse diameter of the former is usually consi- derably smaller than the diameter of the parenchymatous cells, the longitudinal extension is very remarkable. In regard to the majority of elongated cells, especially the prosenchymatous cells of the wood and hast or liber of most plants, we should be very much THE VEGETABLE CELL. 9 deceived if we deduced from the fibrous structure of these organs a great length of the constituent cells ; yet, on the other hand, cases do occur when particular cells exhibit an astonishing length. The prosenchymatous cells of wood generally exhibit only a length of l-3rd to one line, exceeding this last dimension but seldom; as a rule, the bast cells attain abont the same length ; yet in some cases they occm- of far more considerable length, for I found them 1*6 to 2*6 lines long in a Palm (a species of Astrocaryum). The bast cells of flax and hemp are considerably longer, but difli- cult to measure, since it is often impossible to ascertain the com- mencement and termination of a cell Many hairs formed of simple cells also exhibit a very considerable length, especially cotton, the longest fibres of which do not, however, exceed one to two inches. Among the cells of the higher plants the pollen grains are the most striking for their great longitudinal growth, the fili- form prolongation penetrating into the style attaining in long- styled plants like IfiraSiKs longijiora, Oactus grandifiorus, <&c., a lenefth of three inches and more. The most striking examples of large cells are found in the family of the Algse, in many uni-cellular plants, as in Vaucherla, Bryopsis, and especially in Ghara, in the larger species of which the great cells forming the interior of the stem attain the length of several inches, and a diameter of l-3rd of a line and more. C. THE CELL-MEMBRANE. a. Physical Froperties. In most cases the membrane of cells possess a considerable de- gree of stiffness and solidity. But in tliis respect extreme dif- ferences occur between the cells of different plants and of their different organs ; and, moreover, this condition may exhibit ex- treme variations at different periods of the growth of the same cell. The membrane of young cells, also the cells of many lower plants, for example of most Algae, Fungi, Lichens, and the cells of fleshy leaves and fruits are very soft ; while the cells of many woods, e. g., in Palms and Tree Ferns, and those of the albumen of many fruits, exhibit a bony hardness ; and finally, the cells of the epidermis of Eq'wis&t'wm% and Calamus possess such solidity, that it scratches metal, and strikes fire with steel. All membranes are readily penetrated by water, and in the operation become more or less softened and swollen up. The latter phenomenon occurs in a higher degree the younger and softer the cell is ; whether, however, as ScHeiden states, the membranes of nascent cells are actually soluble in water, is more than doubt- ful to me. The swelling up occurs strongly in many thick-waUed cells which in a dry condition have a horny consistence, as in Lichens, Fucoidese, and in certain gelatinously soffc cells (the so- called coUenchyma cells) lying beneath the epidermis of herbace- ous plants. In the short parenchymatous cells no great difference 10 ANATOMY AND PHYSIOLOGY OF appears to occur in the strength of the expansion in the different directions; but in the elongated cells of the bast and wood, the swelling up resulting from moistening takes place principally m the direction of the breadth, and only in a very small degree m the longitudinal direction. The cell-membrane of young cells is completely colourless and transparent ; in fall-grown cells it is frequently imbued with yel- low, red, or brown colouring matters, whereby in many cases the transparency is importantly interfered with. This alteration is very striking in the change of the sap-wood into heart- wood, for in many trees, e. g., in the ebony and yew, the white is converted into a more or less dark colour, without the cell-membrane m- creasing in thickness, while at the same time it acquires a far more considerable solidity and independence of the influence of mois- ture. Ohserv. It is difficult to conceive how some phytotomists (Link, ''Ele- ment. Phil BoC 1824, p. 366 ; Meyen, ''PhysioU i. 30) came to the opinion that cells contract in the direction of their length when moistened, and again expand when dried, since, on the contrary, all cells expand in every direction when moistened. In the elongated cells of the wood the con- traction by drying in the direction of the length is, of course, but small, yet it occurs constantly. In wood of Dicotyledons the longitudinal con- traction from the wet to the perfectly air-dried condition amounts to only 0-072 to 0-4 per cent., while the contraction in tlie direction of the breadth is as much as 4 to 9 per cent. According to Schleiden's experiments, the bast-cells of flax expand only about 0-0005 to 0-0006 ; hut he considers it possible that there was an important error here {Beitrdge, i. 69). Ac- cording to the researches of Ernest Meyer, the Manilla hemp (Fhor- mium ?J expands, when wetted, about l-50th of its length, whHe the increase of breadth amounts to l-5th. I\ Structure. In examining a transverse section of a thick walled cell^ e^g., Fig. 11. .\^ Transverse section throuu;'li the liber-celis of Cocos bo- trijophora. cavity of the cell. Fig. 12. of wood-cells of Cle- matis Vitalba, the bast -cells of Palms, (fig. II), or the thick walled pith -cells of Hoya carnosa, {^g. 12) we find by strong- ly magnifying, that the cell-membrane is not homogeneous, but composed of numer- ous super -incumbent Transverse section through a thick lavCrS COUCeutrical- walled cell of the pith of Hoi/a ^ *^ -,. ,-, carnom. \j surrouudiug the By tlie action of a mineral acid of proper ^V'">'in THE VEGETABLE UELL. 11 F((! IS. degree of concentration the membrane is caused to swell up, ifcs lamellar structure becomes very mucli more distinct, and a great number (often fifty) of separate layers may be detected. By this means the lamellar stiuctiire may be demonstrated even in those cases Id which the unaltered membrane appeared completely homo- geneous ; for instance, in the horny cells of the albumen of Fhy- tdeplias. Usually the wall of the cell is of equal thickness on all sides ; in this case the layers run uninterruptedly round the cavity and form perfect cells encased one within another. In many cases (e, jr., very fi^cquently in the epidennis-cells — fig. 1 3 — and in the brown cells which surround the vascular bundles of the Ferns) the different sides of the cell possess, on the con- trary, a very different thick- ness ; in this case the layers of the thicker portion of the wall are not continued over the thin sides, but are bevelled gradu- ally oflf! This condition alone allows us to conclude with great pro- bability, that the growth of the cell-membrane in thickness does not depend upon the thin mexnbrane of the vouns cell it- self growing thicker by the absorption of new celMo.e, bnt that it arises from a periodical deposition of new membranes upon the already completely developed wall. But the complete confiimation and more accurate knowledge of this process are only obtained through the circumstances next to be mentioned. The wall of young cells having yet very thin membranes, ap- pears perfectly smooth and uniform ; but if the tissue of the same organ is examined at a later period, the walls of its cells are found to have become thickened ; these walls are almost without excep- tion found to be covered with a greater or smaller number of pore- like points or slits, which are distinguished by the name of dots (tiipfel ox pits). A more minute examination of the cross-section of the cells (figs. 11, 12) reveals that these spots are formed by canals which open freely into the cavity of the cell, but are closed externally by the outermost thin membrane of the cell "When all these cir- cumstances are taken together, it becomes most indubitably evi- dent, that the primary membrane of the cell is completely closed and not possessed of visible pores ; that the subsequent deposits, on the contrary, have the form of perforated membranes, and that the deposition of these secondary membranes takes place in the direction from without inwards upon the inside of the primaiy membrane. Cells of tlie Epideniiis of the stem of Yuetmi album. 12 ANATOMY AND PHYSIOLOGY OF Observ, It is now no longer wortii while to give an hi&torical review of tlie opinions that had })een expres&ed as to the strticture of the cell- wall and of the spofcs, before the appearance of mj es&ay " On the Pores of Vegetable Cellular Tibsne/' in 1828. But it is necesbary to advert to the objections which have recently been advanced by Harting and Mulder against my doctrine of the structm-e of cellS; and of the gradual and successive deposition of the secondary layers from without inwards. f/See Harting " Mlhroclieyyi. Onderzoekmgen^'' &c.j in the " Tidshrift voor naturlijke gescMedemSy" XI. J (translated in the Linndia XIX. Harting : " Letter to If. v. Mohl^'—Bot. Zeitwig, 1847, 337. — Mulder '^Physiological Ghemistrij.'' — Mohl " On the Growth of Gell Membranes,'' — Bot. Zeitung, 1846j 337.) I believe I may safely leave unnoticed the objections ad- vanced by Hartig. (^" Beitrage zur Entwickelungsgesch. der PJlanzenP 1843; "Das Leben der Fflanzenzelle.''' J Mulder and Harting attack my theory on both anatomical and chemi- cal grounds, and seek to demonstrate that the cell-membx^ane increases in thickness in the direction from within outwards by the deposition of layers upon the outside of the original membrane, which process of growth is followed, in some cases, by a deposition in the interior of the cavity of the cell, while in particular instances (in the cells of horny albumen) the membrane itself grows thicker by the interpenetration of foreign matfcer. In the first place, my opponents deny that the thin membranes of the young cell are imperforate, and that only the subsequently internally deposited layers are porous, since they, on the contrary, believe, that they found the membrane of young cells to be perforated like a sieve, while a perfectly closed membrane is deposited subsequently on the outside of these closed cells. It is, of course, not for me to decide who observed most correctly, I or Harfcing ; but I must stand by the facts I have stated, and do not believe that Harting would have been deceived in the manner he has, if, instead of selecting only cells having small pits for his observa- tions, he had extended his researches also to cells with large pits, between which the secondary membranes ^i-ppear in the form of narrow fibres ; and had properly regarded the analogy which exists between the structure of the vascular utricles and cells. Harting finds a second reason for his view of the external growth in his micrometrical measurements of young and of thickened cells (Linncea, 1846, 552), by which he arrived at the conclusion that the cavity of the wood-cells expands during the increase of thickness of a shoot, in exactly the same proportion as the unlignified cells, whence he argued that the thickening of their walls is to be ascribed to a deposition taking place upon the outside of then' primary membrane. On the other hand, I consider that I have demonstrated by my measure- ments (^' Bot. Zeitung'' 1846, 358) that exactly the contrary occurs, and that the thickening of the walls is combined with a narrowing of the cavity of tbe cell. — Mulder and Harting deduce a third counter-evidence from the chemical reaction of the cell-wall (which will be sjjoken of here- after). The membrane of young cells is coloiured blue by the action of iodine and sulphuric acid ; in full-grown cells this very often happens only to the innermost layers, while the intermediate acquire a green or yellow, and the outermost membrane a brown, colour, altogether withstanding the solvent power of sulphuric acid, which is not the case with the interme- diate and inner layers. From this my opponents draw the conclusion THE VEGETABLE CELL. 13 Cells of the albumen of SagutyQ!tode^ occurred in all cells. Ho thought that this membrane was distinguishable from the intermediate layer (his Astathe) by definite chemical characters, since it was not coloured blue by iodine and sidphuric acid, like the latter, and agreed in this character with the outermost coat of the cell (which he called the Eustathe). Hartig considered this inner layer as the oldest, the outermost the youngest, of the cell-membranes. The whole of this doe* trine depends upon very imperfect observations. The tertiary membrane of TdxiM is composed of cellulose, it is therefore a true cell-mcm]>rane ; but Hartig seems, in many other cases, to have taken the primordifd ntnch (subsequently to be described) for a layer of cell-membrane, and thus to have classed together structm^es which have notliing at ail in common. Ohsevi), 2. It may not be out of place, after this exposition of the struc- ture of the secondary membranes, to cast a glance at the structure of the vascular utricle, since the different modifications of the structure of the cell-wall are met with again in the vessels, and, indeed, in many cases dis- played much more distinctly than in the cells, so that these conditions were observed in the vessels long before they were known in the cells, albeit much that was incorrect was stated of them. The vessels were divided according to the modifications of the structure of their secondary layers, into spiral, annular, reticulated, dotted vessels, &c. The most widely distributed form is the spiral mssel, for this occurs in all plants which Ftg, 27, Fiff. 28. Fiff. 20. possess vessels ; and I { particularly, in most organs the first ves- sels which appear belong to this form, so that they are met with in the hind- most parts next the pith, of the vascu- lar bundles of the stem. The secon- dary membrane of these vessels is di- vided into one or more (in Mvi^a as many as 20) paral- lel spiral fibres, which as a rule ter- minate in an annu- lar fibre attheupper and lower ends of the vascular utricle. If the vessel is developed in an organ which has already completed its c 2 Fig, 26. Spiral vessel of Jmjpcc- Spiral vessels of SamhiMcus Mhulm. 20 ANATOMY AND PHYSIOLOGY OF Fig. 30. 'INlll jiiiii"'' Mi iraiuiuiii'"'^' fllll jii until'""' h X" .jiiii""" longitudinal growtli, the turns of tlie spiral fibre lie close together (fig. 27) ; but if the organ undergoes elongation after the completion of the development of the vessel, the turns of the fibre ai^e drawn far apart (figs. 28, 29), by the stretching which the vessel sufiers ; consequently, very loosely wound spii^al vessels are usually found in the posterior first-formed portion of the vascular bundle, nearest to the pith, while those lying nearest the bark have close convolutions. The annular vessds (fig. 30) form a slight modification of the vspiral vessels, for in many cases a series of vascular utricles containing spiral fibres are regularly found followed in the same vessel by a seiies of utricles which contain annular fibres, or spiral fibres and annular fibres alternate without any definite rule, often in the same vessel The reticulated vessels occur in manifold modifications, in particular among the vascular Cryptogamia, and in tlie outer youngest parts of the vascular bundles of the Monocotyledons. In these occurs a dependence of the form and distribution of the pits upon the formation of the adjacent parts, similar to that which we have found in the pitted cells. "When several vessels lie immedi- ately upon one another, the walls by which they are coberent together {^g. 31, a) are covered with trans- verse pits, separated by narrow fibres, and these pits occupy the whole breadth of such a side-wall, but are not continued over the angles at which the several lateral faces of the vessel meet. To this form is applied the term sccdarifofiin ducts. But if the wall of such a vessel is in contact with cells by a large or small surface ^^ ^fibre! ^^^^^ (fig- 3i, 5) its pits exhibit the elliptical or rounded form of the pit of the cells, and are sometimes distributed quite irregularly, sometimes arranged in a spiral direction, and the vessel retains the name of reticulated. Yery frequently the same vessel exhibits both these modifications of structure at different points. Lastly, the fitted vessels (fig. 32) which occur in the wood of Dico- tyledons (with the exception of its oldest parts, in contact with the pith) exhibit on those points of their walls by which they are in contact with a second vessel, a more or less abundant quantity of pits surrounded by a line, while the walls borderiag on cells pre- sent the form of reticulated vessels, i. e,j possess pits without a boundary line, or are quite devoid of them. In some cases, for example in the Lime, a tertiary membrane occurs in the pitted vessels, which appears in the form of fibres running between the pits. The septa between the vascular utri- cles do not always become perfectly absorbed ; but in the reticulated^ and especially often in the pitted vessels, Ves'=?el from the stem of a Gourd, contaming both Fiff, 32. Fig^ 31. a V Eeticulated ve^el from a tree Fern. Pitted vessel firom Laarus Saasafras THE VEGETABLE CELL. 91 Fir/. 33. secondary layers are deposited in the form of a net-wurk, or of parallel cross fibres on tlie transverse or oblique partitions of the vascular utricles, while the primary membrane is regularly absorbed between these fibres, so that the open communication between the vascular utricles is not interrupted. Ohserv. 3. In the description of the structiu^e of the cells and vessels, I have mentioned the spiral and reticulated coui*se of the fibres as two distinct modifications of the structure of the secondary membrane. Since ti'ansitions between the two structures frequently occur (fig. 33), and since when the fibre is reticulated the pits are arranged more or less dis- tinctly in spiral lines ; since, moreover, the pits scattered over an uniform membrane frequently have a lungish form, and their long diameter like- wise situated in an oblique spiral direction, the thought readily presents itself that spiral structures form the basis of secondary membranes of all cells and vessels, and that the other forms owe their origin to subsequent transformation of the spiral cell and spiral vessel. The view has been expressed by most phytotomists in reference to the vessels ; but the conceptions that have been formed of the processes occurring in this metamorphosis were for the most part of rather a rough character. Thus the notion was extensively embraced, that the spiral fibre could not follow the expansion which the vessel underwent during its growth, and tore up into fiagments, wiiich again united into rings, and thus brought about the formation of annular vessels. Completely as this idea, which was a contradiction to all observation, had been refuted by Molden- hawer, it remained a standing article in all phy- totomical writings up to " MeyerCs Fhydologie,^'' Schleidon (" On the Spiral Structures in the Vege- table Cell" Flora^ 1839) sought to explain the origin of the annular vessels from the spiral vessels in a manner less easy to refute, assuming that in each case two turns of a spiral fibre grew together into a ring, while the rest of the fibre, running between ^^^iSi^sMk^S^li^S *^^ these rings was subsequently dissolved. My own hyindiim, observations ("(9?i the Structure of the Annular Yes- sekf^' in my " Vermischte Schrifien^^ 285) compel me to declare most decidedly against this explanation, since they demonstrated the rings to be primaeval, original structui-es, from their very first appear- ance, and the seeming transitional stages from spiral vessels into animlar vessels to be permanent intermediate forms between the two kinds of vessels. The idea that the reticulated vessels are produced from spiral vessels has been more extensively defended, and especially lately by Schleiden and linger (Linmmob, 1841, 394y). Nothing appeared simpler than the assumption that cross fibres were formed between the convolutions of the spiral fibre, and that the spiral was thus converted into a reticulated vessel. But two circumstances lead me to reject this notion most de- cidedly. In the first place, observation of the vessels in which the second- ary layers have just begun to be formed^ gives evidence that the delicate 22 AN"ATOMY AND PHYSIOLOGY OF fibres fir&t deposited are already connected into a net-work, as is especially Been in tlie exaaiination of tlie young roots of the PalmB. On tlie otlier hand; tliis conception of the transition of a spu-al vessel into a reticulated vessel is ineonipatil>le witli the mechanical condition of the fibre. When iwo spiral vessels lie upon one another their fibres must cross, since in the majority of cases the fibres of the two vessels run in the same direction (homodromons) ; but we find that when two reticulated vessels lie against one another, the fibres in ibe two vessels are placed transversely, and cor- respond accurately together in position; which could only result from the fibres of the two vascular utricles losing their original spkal direc- tions, and one being pressed down to the right, the other bo the left, imtil tLeir situations should exactly correspond. Who will believe in such a motion of fibres, which are not free but adherent to the vascular utricles, themselves coherent together"? and who bas seen anything of the kind'? A process of this kind might be held to be possible so long as we were ignorant of tbe true structure of the vessel, and believed that the fibre lay free in the cavity of the vessel, an error which formet-ly prevailed ex- tensively, and which one would not have expected to have still met with in a writing of Schleiden's ("^e^^?m^e," i. 188). And if the incredible statement, that the fibre performed such a journey over one side of the vessel, were actually assumed to be true, how should the prolongations of it over the other sides of the vessel behave ? Would these tear away or be pulled backwards and forwards, to restore by their more oblique posi- tion what was lost in their spiral course over the other side 1 Instead of the confusion which must necessarily arise from this, we meet with the most beautiful order. If the lateral walls of the vessel are in contact with cells, we find its pits corresponding with those of the cells ; if one part of a vessel is connected with another vessel we meet with hoiizontal, slit-like pits. Thus we see clearly that one elementary organ influences the organization of an adjacent one in a definite manner, but we are no- where able to observe, that an organ already developed to a certain extent allows its already organized parts to perform movements in order to place themselves opposite the parts of the neighbouring organs. Since none of these matters can be seen, the processes are referred back by Schleiden to a time at which the observation is impossible. Thus he says f^' Grwndz. der wiss. Botamk^' i. 228^), it seems to him very probable that the spiral is in existence long before it is visible under our optical insti^uments, since it is composed at first of a substance which does not differ optically from the ccU-wall and cell-contents ; hence, many forms might be referred to the spiral only at that epoch, if we assume that the intermediate stages were run through before the structure was yet visible. I readily allow the author to speculate as to the course of fibres which cannot be seen, but I must be excused from following him into this region. Yalentin, indeed, who originated the theory of the expansion of the spiral fibres in all directions {^^Eep,f. Anat and Fhys^ i. 88), believed that this could be demonstrated by observed facts, for he stated that he had found the secondary mem- bmne making its first appearance in the form of a granular substance, the granules of which at first exhibited no definite order, but were subse- quently arranged into spirals, and became connected into the spiral lines which might be distinguished on the completely formed membrane ; a view which has not acquired confirmation from any subsequent observer, 'HE VEGETABLE CELLf ^o It is scarcely \yorfcli mentiomng tliat; Meyen {'^ Fhysiohglep i. io) set lip the tlieory tliat not only tlie secondary layers, but also the primary membrane was composed of distinct spii'al fibres grown together. Ho was led to this opinion principally by the cells containing a very fine spiral fibre, of a Stells gathered by laini in Manilla, the structure of which he completely misapprehended, since he imagined that the fibres formed the primary membrane, while they belonged to the secondary. In conclusion, it may be remarked that Schleiden's hypothesis ("-5e^ trage^'i. 187), that in the formation of the secondary layers there exist at first, at least, two spiral bands, one corresponding to the ascending current, the other to the descending current of the mucilaginous formative sub- stance, the two extremities coalescing at the ends of the coil, and that in most cases these become blended together at a very early period, is simply to be banished into the region of dreams. The opinion which formerly prevailed widely, and which Link (" FML Botanr 1837, i. 177) still defends, that the pits of the scalariform ducts and pitted vessels are the remnants of the fibres of spiral vessels broken up into fragments, requnes no further refutation. Holes in a membrane can scarcely be considered as elevations. Ohserv, 4. In the preceding I have spoken of cells and vessels as clearly separated organs, because in most plants the fully-developed cell differs in a marked manner from the fiilly-developed vessel ; but it must not be forgotten that transitional structures occur. One form, the porous cells, has already been mentioned ; these come near to the vessels in the large open pores, by which they communicate with each other, but they are dis- tinguished from those by the fact, that they form a parenchymatous tissue in the manner of cells, lie upon the surface of oi'ffans, and, in part, in jSphagnwn (-^s^. 33, B), open eVen to the external dr/yMe thf vascular utricles are always combined into tubes, whicli ran among the cells in the interior of plants. Another intermediate structure occurs in the vas^ cular Cryptogamia, particularly in the Lycopodia and Ferns, as well as in the Coniferse and Cyca- dejB. In these plants we meet with the peculiar condition that the wood is not composed of a mixture of elongated cells and vessels, but of ele^ mentary organs of one kind, which resemble pro™ senchymatous cells in their form, and vessels in the structure of their walls, and give evidence of their near relation to the latter, in the fact that the prolongations of the vascular bundles of the stem%ntering bto the leaves, contaii perfectly developed vessels ; as also ta the fact, that in the stems of Coniferse and Cycadese, the innermost elementary organs, bordering on the pith are per- fect spiral vessels, and that in B^ilhedra particular ■wood-cells become united into perfect pitted ducts. Observ. 5, Perhaps it is not altogether superfluous, ia reference to the terminology of the pitted cells and vessels, to remark that since the struc- tui^e of the pits (tdpfel) and their distinction from actual holes have been m'\^. Porous cell fiinuslicd with am*-ular fibros from tlie leat'of 24i ANATOMY AND PHYSIOLOGY OF uiiderbtood, it is tlie more general custom to apply tlie term pit (tiipfe!) to the canals perforatmg the secondary layers, and closed externally by the outer membrane of the utricle, and the term pore to the same canals when the primary membrane has been absorbed and the orifices of the utricles open freely into each other. Schleiden, on the conti^ary, uses the name of porous instead of pitted (getupfelten) cells, calls the pits pores, and the pores holes (locher), because {^^ BeitragCj' i 189) according to Adelung and Hemsius, the word tuj^fel (dot) means a shallow depres- sion, or a slightly elevated spot upon a surface. I will not enter mto any etymological controversy against such authorities, but keep simply to my Swabian German, and am consequently of opimon that a panther's skin is geti(/pft (spotted or dotted), although its spots are neither depressed nor elevated * c. Chemical Conditions. The basis of the memlbranes of all the elementary organs of vegetables consists of neutral hydro-carbons ; in almost all cases, and perhaps "withont exception, of cellulose. Cellulose is colouiless, insoluble in cold and boiling water, alcohol, ether, and dilute acids, almost insoluble in weak alkaline solutions, soluble in concentrated sulphuric acid ; it is converted into dextrine by dilute sulphuric acid at a boiling heat. When imbued with iodine it becomes coloured indigo blue if wetted with water, this colour appears more readily under the conjoined influence of water, sulphuric acid, and iodine. According to Payen, the formula of its composition is C12 H20 Oiq. Cellulose probably does not occur in a pure condition in any cell-membrane, since a series of both organic and inorganic com- pounds are deposited within it ; in which fact is to be sought the explanation of the manifold physical and chemical differences which are exhibited by the membranes of the same cell at different periods of their age, as well as by the cells of different plants. The combination of ceU-membrane with inorganic substances is a very general condition, for the only examples of exception to this which have as yet been met with, are a few species of Mould Fungus (Mulder), into which, however, ammonia might still have entered as a substitute for the fixed bases. In all other plants a skeleton (the ash), corresponding to the form of the membrane, and composed of the alkalies, earths, and metallic oxides which had been deposited in it, remains behind after the cell has been burnt. The younger an elementary organ is, the more abundant, in general, the alkalies appear to be ; the older it is, the more exclusively the earths and metallic oxides seem to be combined * Some confusion exists also in our English terminology, the terms dotted and pitted tissues are indifferently applied to these structures, called by the Germans getvp/elt. I have used the v^ord pitted throughout this translation to express this term, because it indicates the true structiu:^. THE VEGETABLE CELL. 25 with its substance. The higher the degree in which the latter occurs, the harder the membrane becomes, as is shewn by the relation of the heart- wood to the sap-wood, and in a still greater measure in many seed-coats of a bony consistence, e, g , the peri- carp of Litfiospermum, which contains much lime, the epidermis ot Equiseturti and Calamus^ in which a great quantity of silica is deposited. However, we are without any accurate knowledge of these conditions, in spite of the countless analyses of ashes which we possess, for these give the product of ash of the cell-contents and cell-membrane together. The deposition of organic substances is not less general than that of inorganic compounds, at least in particular layers of cell- membrane. Among these the nitrogenous compou.nds are cer- tainly the most widely distributed. They do not occur in the membranes of cells which are just at the commencement of their development, for these are not coloured yellow by tincture of iodine, yet scarcely a full-grown cell is met with in which this is not the case. That these nitrogenous compounds belong, in many instances, and especially in the cells of the wood, to the series of proteine compounds, we have evidence (as Mulder pointed out) in the violet colour which hydrochloric acid produces after long oper- ation, and in the yellow colour which ammonia produces after a previous action of nitric acid. Tlie presence of these compounds explains how, accoiding to Chevandier's analysis, wood contains 0*67 to 1*52 per cent, of nitrogen. The darker yellow a cell -membrane is co- F%g,ZL loured ij nitrogen, the more Wy it withstands the action of sulphuric acid, and the more difficult it is to obtain the blue colour by the combination of this and iodine. In most parenchymatous cells, especially in the tL walfed, this blue colour usually appeal's so intensely that the original yellow tint totally dis- appears ; ink tick walled cells, on the contrary, especially those of wood, the stronff yellow colour is not altogether ^ ^ „ ^ ^ ^ *^ - , T T T - / Liber cell of Cocoa ootryophora, overcome, and the colour assumes a dirty a, PnimtiTe membrane, h, secon- green tint; lastly, in others no blue co- ^iTA'Z^X^"' lour is produced at all, and the membrane offers such resistance, even to concentrated sulphuric acid, that it either only swells up sHghtly or remains (juite unaltered, only becoming coloured deep brown ; as is the case particularly in ex- ternal layers of epidermis-cells and the outermost layers of almost aU full-grown, cells, especially those of wood. This outermost layer may readily be taken for the primary membrane of the cell ; but as a rule it is composed of several super-imposed layers, and fre- quently contains the outer ends of the pit canals (fig. 34), whence 26 ANATOMY AND PHYSIOLOGY OF it is quite clear that in an anatomical sense it is not a well-defined membrane, but tliat it is composed of the primary membrane, and a few layers which belong to the secondary deposits, and which have undergone the same chemical changes as the primary membrane itself. Besides the nitrogenous compounds and the colouring matters which are diffused thi-ough many cells, especially those of the wood, the membranes of a great number of cells also afford a series of compounds devoid of nitrogen, which sometimes have a differ- ent composition from cellulose, sometimes are isomerous with it. Compounds of the first kind in which carbon, and, still more, hydrogen, are contained in relatively greater quantity than in cellulose, occur in the cell-membranes of fully developed wood, on which account all the earlier elementary analyses of wood give a false result, since the mixture of different compounds forming the cells of the wood was taken for a simple combination (the so- called woody fibre). While it is beyond doubt that all the compounds differing from cellulose in composition, form interstitial deposits in the cell- membrane composed of cellulose, entering into it subsequently to its first production, it is on the other hand doubtful whether the compounds which are composed, like cellulose, of carbon and the constituents of water, and which are either isomerous with cellu- lose, or differ from it perhaps only in containing a smaller amount of water, are to be regarded in like manner as depositions in the cellulose, or whether they replace cellulose and form the cell- membrane itself, or at least some of the layers of it. Doubts in reference to this point are raised, especially by the cells of many of the lower plants, e. g.^ the cells of many Lichens, as of Getraria islandica, which are partially soluble in hot water, and yield a substance similar to starch ; also the cells of many Algse, as 8phcB- TocoGcus erispus, which yield a mucilage by boiling, and of which Kiitzing ("JPhycologia generalis") assumed that they were com- posed of a pecuHar compound, named by him phytogelin. In none Sf these caL can we Lte with any Ltsil/JetUr^ or what share, cellulose takes in the formation of these membranes; and as little whether or not inorganic compounds, which might modify the characters of the cell-membrane by their action, are com- bined with it. We labour under the same uncertainty in regard to the differences which distinguish young cells from those in older conditions. Thus the membrane of the former swells up strongly in water, and is not coloured blue by iodine alone (but only by . iodine and sulphuric acid). We have not at present any definite facts to enable us to express a decided opinion whether we are to assume that the compound of which the young cell-membrane is formed is essentially different from cellulose, and during the pro- gressive development of the cell undergoes a chemical metamor- phosis, a change of arrangement of its constituents or the like, or THE VEGETABLE CELL. 27 tliat this compound is replaced by cellulose, or that both are to be regarded as the same compound only distinguishable by slight differences in their conditions of aggregation ; or that the differ- ences are caused by the interstitial deposition of various foi^eign compounds. The same occurs in reference to the substance of those cells which are coloured blue "with the same facility as starch, by the action of a weak tincture of iodine, but differ from starch by their behaviour to warm water, as is the case in the horny albumen of many plants, e. g,, of Cyclamen^ in the cells of the embryo of ScJiotia, &c. (See " On the Blue Colouring of Ve- gcbahle Gell-membrane by Iodine,'' in my " Verniisckte Schriften,'' 335.) Ohserv. 1. The credit is due to Pay en (^'Memoires sur les demhppe- menu des vegetaux,' 1844) of having demonstrated that the substance of all cells, from the liiglie&t plants down to the Fungi, when pmified from foreign deposits, exhibits the same composition, and assumes the blue colour of cellulose on treatment with iodine and sulphuric acid. Accord- ing to his views the cellulose occurs in a tolerably pure condition in very- young cells^ while the membranes of older cells are combined more or less with foreign organic or inorganic compounds (which he called incrusting substances), through the presence of which tlie physical and chemical pro- perties of the cell-membrane undergo alterations. These incrusting sub- stances may be more or less completely extracted by treating the cellulose tissue with acids, ammonia, alcohol, ether, &c. Thus, according to Ms statement, nitrogenous substances and silica occur in the cuticle, pectate and pectinate of lime and of the alkalies in the thick walled epidermal colls of the Gactem, inuline in the cells of the Lichens and Algse, and in the hard cells of wood capable of being polished three or four compounds, designated by Payen lignose, lignone, lignine, and ligninose^ substances which are richer tban cellulose in carbon and hydrogen. Ohserv, 2. We owe to Mulder (^^Physiological Gh&mr ) very extensive researches on the chemical conditions of the walls of the elementary organs. He also, like Payen, arrived at the result, that the membrane of all young organs consist's of cellulose in almost a pure condition (the for- mula of which he determined as O24, H42, O21) \ but in reference to the alterations which the membranes undergo in the course of time, he pro- pounded totally different views. He here starts from the fundamental doctrine that a given layer of an elementary organ which is not coloured blue by iodine and sulpluuic acid, does not contain cellulose ; that there- fore, when the same layer can be demonstrated to consist of cellulose in the earliest periods of the growth of the elementary organ, the cellulose must have been displaced by other compoxmds, or that if this origin from a layer of cellulose cannot be demonstrated, it is a later formation, and has been composed of other compounds from the first. In this way he arrives at the conclusion, that the membrane of the elementary organs increases in thickness in three ways : — 1, By the deposition of younger layers upon the inside of the membrane ; this occurs in the vessels and in a doubtful manner in the thickened pith-cells of Koya canrnosa. 2, By the deposition of layers upon the outside of the elementary organs, which occurs generally m cells j in parenchymatous cells layers of the same kind 28 ANATOMY AND PHYSIOLOGY OF alone are generally deposited ; in wood-cells, on tlie contrary, first an outer coat is formed, and then subsequently intermediate layers of consi- derable tliickness are formed between this and the inner primary mem- brane. 3, The new substances are deposited in the cell-wall of many cells (in the horny albumen of PJiytehphas, Iris, and the so-called coUen- chymatous cells), and therefore the wall does not exhibit lamellation. The constitution of these different deposits is described as very varied. Proteine is shewn to be merely an infiltrated matter, taking no part in the formation of the cell-wall, and is wholly wanting, or only just trace- able in very young cell-membranes j but it occurs in the intermediate substance of all old wood-cells, and most old pith-cells, but not in bark- cells or collenehymatous cells. The following compounds are p>articularly noticed as forming definite layers of the elementary organs. Intermediate wood-substance (the formula of which is stated at O40; Hse? 0%), a com- pound which is coloured yellow by iodine and sulphuiic acid, swells up in weak acid and dissolves in stronger ; it gradually displaces the celhilose more or less perfectly in the secondary layer of vessels, forms the outer layers of pith-cells and the intermediate of the wood-cells, in which it becomes the more intimately combined with the cellulose the further the layers he toward the inside. Bxlernal wood-substancej which is coloured brown by iodine and sulphuric acid, and does not dissolve in the latter ; it is stated as probable that this is isomerous with the intermediate wood« substance, but (as in the woody matter of the putamen of hard fruits) is distinguished from it by containing ulmin. It forms the outer layer of wood-cells, scalariform ducts, and pitted vessels. Besides these more generally distributed compounds, there occur other peculiar, less exten- sively prevalent, compounds not yet fully characterized, one of which formitL cuticle; a^oLr tLe cel/of corkfanotler the cJUs of the horny albumen of Iris and Alstrmmeria. The following are regarded as incrust- ing compoimds, penetrating into the substance of the cell-wall : pectose in the cells of the collenchyma, of the Apple, &c. ; starch in Cetraria islan- dica ; vegetable mucilage in Sphmrococcus crispua ; and a peculiar sub- stance isomerous with cellulose, in the cells of the albumen of Fhytelephas. My own investigations {^^Investigation of the question ' Does cellulose form the basis of all vegetable membranes V^^—Botan. Zeit 1847, 497) com- pel me to declare most distuictly against the view of Mulder's, that a great proportion of the layers composing the membranes ai^e from the first composed of compounds difierent from cellulose ; and also against his opinion as to the relative ages of the layers, deduced from these pro- positions (which I have already discussed above under an anatomical point of view). I found that the application of iodine and sulphuric acid, in which Mulder places such unconditional trust, is a means in the highest degree unsafe for deciding whether a membrane contains cellulose or not. My researches shewed me that the infiuence of sulphuric acid was by no means necessary for the production of the blue colour in membranes which are not strongly incrusted, as in the parenchymatous cells of succulent organs, but that iodine and water alone are sufficient ; while in full-grown and hardened cells sometimes the primary membrane alone, sometimes even a greater or smaller portion of the secondary layers had, through the deposition of foreign substances, altogether lost the property of becoming blue on the application of sulphuric acid and iodine, although they were THE VEGETABLE CELL. 29 still composed of cellulose, and iodine alone would yqyj readily produce a blue colour in all their membranes after the infiltrated matters had been removed. The means I employed to remove the infiltrated sub&tances were caustic potash and nitric acid. The first proved to be most effective in the cells forming the surfaces of plants (such as epidermal celL, periderm and cork) ; a maceration for twenty-four to forty-eight hours in strong so- lution of potash, at common temperatures, caused iodine to produce a pm^e blue colour in all these cells. The application of potash is not so effective in the cells situated in the interior of the plant, but that of nitric acid always answers the purpose completely, either when the preparation is left to macerate for a length of time in dilute acid, or is boiled in acid of mo- derate strength until the yellow colour which it assumes at first has dis- appeared again. After this treatment, the whole of the layers of all elementary organs are coloured a beautiful blue by iodine even when they ofier so great a resistance to the action of sulphuric acid before the treat- ment with nitric, as is the case in the outer membrane of wood-cells and of vessels, and in the brown cells at the circumference of the vascular bundles in Ferns. After these experiments there cannot be any doubt, that cellulose forms the ])asis of all the membranes of the higher plants, that the greater or less resistance of many membranes to the combined action of iodme and sulphuric acid, is caused by infiltrated foreign com- pounds, and that the "substance" of cuticle, of cork, and the "outer and middle wood-substance," regarded by Mulder as peculiar compounds, are combinations of cellulose with foreign infiltrated deposits. Of what nature these deposits are, wliich interfere with the reaction of cellulose, future researches of chemists must decide. Ohserv. 3. Schleiden takes up quite a different point of view. {'^On Amyloid.'"' Beitrage, i. 168. "^ome remarks on the suhstcmce of vege- table nwrnbranmr Beitrage i. 172.) Without regarding that the cell- walls are not composed of one chemical compound, but that they have a series of substances deposited in them, possibly exerting an influence upon their properties, — ^he considers the differences which are observed in the cell-membranes as unconditional proofs of difference in the sub- stances of which they are fox^med, and believes that the compounds dis- tinguished by chemists, forming the series of hydrates of carbon, are but a very sparing selection from the infinite multiplicity of compounds belonging to this series, occurring in plants. According to his views, the plant forms a fundamental substance, wliich remains the same in re- ference to its elementary composition, *iut is capable of infinite modi- fications by internal imperceptible changes, and also, in part by the in- crease or diminution of chemically combined water : forming a series, the adjoining members of which differ imperceptibly to us, sugar being the lowest, and the substance of perfectly developed membrane the highest, of the members, which become more and more insoluble in water from below upward. Three compounds, in particular, of this series, forming ceE-membranes, are minutely characterized according to their behaviour to iodine and water: 1, Cellulose, of which it is stated that it is not coloured blue by iodine, when in a pure condition {"Grundz. der wiss, BotaniJc^'^ 3rd ed., L 172), which is decidedly untrue. 2, Amyloid; — Schleiden used this name to signify the substance, announced by himself and Yogel, composing the horny cells of the cotyledons of Scho^i Ey- 30 ANA.TOMY AND PHYSIOLOGY OF menma^ Muctma, and Tamarmdus, wliicli are readily coloured blue by iodine. According to his account amyloid dissolves in boiling water, and its compounds with iodine are dissolved in water with a golden yellow colour. The latter is decidedly incorrect, and in regard to the former, Schleiden himself says {" £eitrage,'' i. 167), only the intermediate layers were dissolved even after twelve hours boiling, and all the cellulose tissue remained. 3, Vegetable Jelly; — under this name Schleiden compiiscd a series of compounds, wliich chemists mention under different names fJBas- sorm, Cerasin, Pectin, Gelin, (fee. J, but which he united on account of their property of swelling up strongly in water and not becoming coloured by iodine. He ascribed to this substance the property of gradually be* coming difiriised in cold water, and believed many vegetable cells to be composed of this substance, transitions from it existing on the one hand (through the cells of the Fucacese) into cellulose, and on the other (by many kinds of horny albumen) into amyloid. Excepting the statements that cellulose is not coloured by iodine, and that there axist cells soluble in water, there is no doubt of tlie correctness of the anatomical founda- tions on which this theory rests. But on the other hand, there is jxist as little doubt that the whole of this representation of the infinite multipli- city of neutral hydrates of carbon and the distinction between them ac- cording to their greater or less expansion in water, and more or less facility with which they are coloured by iodine, could only be considered as estlbHshed, whe. i/was proved t J the substaace o/vegetable oeUs possessed this property in its pure condition, and that these differences were not caused by foreign deposits. Since not only is this proof wanting, but, on the contrary, the most definite evidence exists that the chemical and physical properties of vegetable membranes can be modified in the greatest degree by infiltrated matters, Schleiden's view is devoid of any solid foundation. B. CELLS IN THEIR RECIPEOCAL CONNEXION. Leaving cut of view the lowest plants, and the spores and pol- len-grains of the more highly organized, cells do not occur isolated, but grown together in great numbers in connected masses ; in this manner they form the so-called cellular tissue, contextus eellulosus (parenchyma or prosenchyma, according as it is com- posed of parenchymatous or^osenchymatous cells). From the structure of the cell, as a closed vesicle formed of a special membrane, it follows that in cellular tissue the partitions between any two cell-cavities must necessarily be composed of a double membrane, and this may be readily observed in reference to the secondary layers, in all thick walled cells, by means of the microscope, for it is clearly seen, that the individual layers of the membranes surround the cavities of the cells concentrically, and that the secondary layers of the several cells are separated from each other by the primary membrane. Observ. It is by no means so simple an affair as it seems at first sight to determine the limit between two cells. Formeidy, when observers were restricted to weaker and less perfect magnifying instruments, the bur- TFIE VEGETABLE CELL. 31 foce of the cross section of tlie primary membrane appeared as so narrow a line, tliat it was taken for the boimdary line between two neighboimng cells, and was drawn as such. Subbe(][iiently, when the knowledge of cellulose structure had progressed farther, the primaiy membrane was distinguished from the secondary layers, and the outermost layer of cell- membrane was seen under stronger microscopes to have a clearly visible breadth (or thickness), the idea remained of an easily distinguishable boundary line between the two coherent cells, and such a line was even figured. This, as Hartig correctly observed, was untrue, for om* micro- scopes, do not shew any boundary line between the two coherent piimary membranes (see figs. 21, 22, 2i5, 32, 44). When Hartig drew from this the general conclusion that no limit exists, and that the outer membrane of the two cells is common to both, his induction was too hasty. The impossibility of seeing a line of demarcation with our microscopes, war- i^ants, ct priori, nothing more than the conjecture that our present instru- ments are not yet sufficiently perfect for the purpose. It is self-evident under these circumstances that nothing has been accurately made out as to the manner in which cells are connected. The cells cobering together may be separated from eaci other; in very succulent tissues, as in the parenchyma of many juicy fruits, a slight pressure suffices for this ; in somewhat firmer tis- sues the connexion of the cells may often be so loosened by boil- ing in water or by freezing, as to become easily separable ; while in very solid tissues a long maceration in water or a short boiling in nitric acid is necessary. It might be imagined that the double nature of the outer membrane could be readily demonstrated by this separation of the cells, but wrongly, for I found that the outer membrane, when distinctly perceptible, was not split into two layers in such cases, but torn into pieces, some adhering to one and some to the other cell, so that the separated cells were composed chiefly of secondary layers.* It has been remarked already, in the description of the form of cells, that the flat faces of cells meet at sharp angles in compara- tively few cases, since the corners and edges are generally rounded off. It follows necessarily from this condition, that the cells are not, for the most part, coherent together by their whole surfaces, but leave empty spaces between them, which run along the edges of the cells in the form of triangular canals having no special walls of their own, opening into each other at the corners of the cells, and so forming a net- work of narrow and wide tubes branch- ing throughout the whole plant, to which the name of intercellu- lar 'passages has been applied {see figs. 6, 7). In living plants they are, with few exceptions, filled with air. * Schultz has lately made known a process for isolating the conjoined cells even of woody tissues. It consists in boHing them for a short time with chlorate of potash in nitiic acid. It is not clear, however, that thm does not dissolve the outer membranes. — A. II. ^9 ANATOMY AND PHYSIOLOGY OF Mg. 35. Intercellular passages occur mostly between parencliymatous cells; they are frequently absent from prosenchyma, or when pre- sent, are, at least, very narrow. They are closed in most places at the surface of the plant, since the parenchymatous cells which form the outermost layer of the plant are, in general, and in all parts growing under ground or in water without exception, accurately in contact at their angles ; on the other hand, on most organs ex- posed to the air, especially on the lower sides of leaves, there occur little ox^ifices bounded by crescent-shaped, curved cells, sto- mates or stomata (fig. 85), which allow a free communication between the air contained in the intercellular passages and the atmosphere. The more regularly polyhedral the cells are, the more do the intercellular passages take the form of regular, nar- row canals (see fig. 7) ; on the other hand, the more globular the shape of the cells (fig. 6), and in a still higher degree, the more an unequal growth has caused them to approach the form of the stellate cell (fig. 10), the more do the intercellular passages take the form of irregular cavities, and the more spongy becomes the tissue of the organ formed of such cells, since the space occupied by the intercellular passages then becomes more equal to, or in ex- treme cases, many times surpasses, that filled by the cells. The lower side of leaves and corollas are formed of such tissue, moderately spongy, the pith of Juncus effusus gives a very highly developed example. In other cases the intercellular passages lying between regular polyhedral cells become expanded at particular points into larger cavities, or into long canals, which latter are frequently interrupted at certain distances by partitions composed of stellate cells. This is the case in the stem and in the leaf-stalk of many water- and marsh-plants, in which the wide, regular air-canals are often sepa- rated from each only by a single layer of parenchymatous cells ; there also exists a roundish air-cavity (breathing -cavity, Ath- Whungshohle) beneath each stomate. Canals and cavities of this kind serve in other cases as reservoirs for peculiar fluids secreted by the neighbouring cells, e. g., for balsams in the Coniferse, for etherial oils in the IJmbelliferge, Aurantiacese, &c., for gum in the Limes, Gycadese, and for milk-sap in Bhus, In many cases the spaces between the cells are filled up with a solid matter, the intercellular substance, which is secreted by the cells upon the outer surface, and sometimes only imperfectly fills Epidenixis of tho lower face of EelU' hoTusfcetidus a, stomate. THE VJEOETABLE CELL. S3 Transverse section tliroiig^li the albumen of So- pJiGra japomca , cj, intercellular substance , by cavity of the cells. tlie intercellular passages, but usually forms a dense mass in it and quite obliterates its cavity. This occurs in remarkable quan- tity in tlie tissue of many Algse, especially of the Fucoide^, the Nostochineae, in the cortical layer of many Lichens, in i^^>. 36. the Albumen of many Legu- ,| a minos^, e, Cells of the epidenni& of tiho upper face of tlae leif of Mmia car w^a a, the portion ot tlicii wallb *ic(iiniiu„ a 3 dlow colour witli lodme Fiff. 41. the enter wall exliibitb tliese properties ilowu to a certain ileptlij so that a layer (fig 4:0, a) is thus formed, which is most {strikingly distinct from the subja- cent ceils, and when the latter have been dissolved in sulphiu'ic acid, remains behind as a continuous and apparently homogene- ous membrane. Since Ad. Brongniait (''Ami. des Be. Nat, jSer,,'' § i, 65) had dis- covered that a continuous membrane, not composed of cells, called by him cuticula, might be separated by maceration from the outer surface of the epidermis, it ap- peared natural to suppose that the layer just spoken of, which is fre- quently very thick and is coloured brown by lodme and sulphuric acid, was this cuticula, and to ascribe its origin to a secretion upon the outside of the epidermis-cells, a process of which Schleiden ev^n gave a detailed description (" Gnmdz. der wiss. Bot.^'' 1st ed. i, 2d>B). This view, however, proposed by Trevii*anus, and defended by linger, Harting, Mulder, and otheis, is in great part wx'ong. The so-called cuticle consists, with the exception of a layer extremely tlim in most plants (fig. 41, a), of the thickened walls of the cells, which are infiltrated with a sub- stance coloured brown by iodine, to which they owe their power of resisting the action of sulphuric acid. When this substance is removed by caustic potash, not only is the composition out of cell-membranes evident, since the separate layers of these become visible, but iodine now very readily produces a blue colour (^'Bot. Zeitung,'' 1847, 592). This composition of the so-called cuticle, of cell- membranes, is seen beyond all doubt in the epidermis of an old stem of Viscum alhwn {^g. 42) ; the epidermis-cells consist here of two or three geneiations enclosed one within another, of which all the thick- ened walls on the outer side have become blended together into a membrane composing the cuticle (H. V. Mohl, " Ob the Bpidermis of Viscum album;' ~Bot Zdtmig, 1849). T call these layers belonging to the epidermal cells the cuticular layers of tJie epider^nis, to dis- tingiiish them from the mass secreted on the outside of the ceUs, the true cuticle, which is soluble in caustic potash, in most cases forms but a very thin coating over the epidermal cells, and only rarely, as in the shoots of Mphedra, and the upper surface of the leaves of Ofca% forms B 2 The epideraijs of the npper si THE VEGETABLE CELL. 53 ing one or more sharply circumscribed round granules (the nucle- oli, Kernhorperchen) ; the large round bodies are called the nuclei (zellen-hern) or cytoblasts. The nuclei are usually smaller at their first appearance than they are afterwards, so that their growth is unmistakable. The surface of perfect nuclei appears smooth and clearly defined, but it cannot be decided with cer- tainty whether we ought to distinguish an enveloping membrane and contents distinct from this, or to ascribe the membranous as- pect of the outer layer to a somewhat greater density ; the nucleoli always appear solid at first ; they often become hollowed out into vesicles subsequently. The substances both of the nucleus and of the nucleolus are coloured yellow by iodine. Ohserv. OiDinions differ very much as to the mode in which the nucleus is formed from the granular protoplasm. Schleiden was the firbfc to dis- cover the import of the micleus and to trace its development. Accord- ing to Ms views (" Grundzuge^'' 3 ed. i, 208) they originate by the formation of large granules in the protoplasm (afterwards the nucleoli) and other granules becoming heaped up around these, and the whole becoming more or less blended together and united into the nucleus. According to Nageh's views (^^ ZeltscIiTifi. f. wi$s, Bot. Ill, 100, Hay /Society's FuhUca- tions,'' 1849, p. 166), the nucleus is not formed by the union of a consider- able mass at once, but appears first as a very minute structure, for tlio rudiments of the nuclear body may be distinguished while they are yet little larger than the globules of the protoplasm. He also assumes that the nucleolus is formed firsfc, and then a layer of protoplasm is deposited around it, which again becomes enclosed in a gelatinous membrane not coloured by iodine ; JEofmeister {^^JSntwich d. Pollens,^' in ^^JBot. ZeiZ^ 1848. "Die Mnstehung des Embryo,'' 1849, ^2) declares distinctly against both these opinions. According to Ms researches, the formation of the nucleus is not preceded* by the origin of nucleoli, but the nucleus presents itself first under the form of a globular drop of a mucilaginous fluid, wMch be- comes coated by a membrane over its outer surface. In many cases no trace of a nucleolus can be seen in the nucleus at first, and one or more (up to twenty) are subsequently formed in it, while hi other cases one or more granules of a more solid substance swim in the fluid of the nucleus from the very first, but not all of these are necessarily developed into nucleoli, for only some of them can increase considerably in size and ac- quire a membranous coat, the others becoming dissolved. Leaving out of the question the membrane of the nucleus and of the nucleoli, the exist- ence of wMch I never could satisfy myself, this latter view appears to me the more correct ; that of ISTageli decidedly wrong. The second mode of origin of a nucleus, by division of a nucleus already existing in the parent-cell, seems to be much rarer than the new production of them, for as yet it has been observed only in few cases, in the parent-cells of the spores of Anthoceros, in the formation of the stomates, in the hairs of the filaments of Tra- descantia, &a, by myself, Nageli, and Hofmeister ; but it is pos- sible that this process prevails very widely, since, as the preceding statements shew, we know very little yet respecting the origin of 5h ANATOMY AND PHYSIOLOGY OF nuclei. Nageli thinks tliat tlie process is similar to tliat in cell-divi- feion, the membrane of the nnclens forming a partition, and the two portions separating in the form of two distinct cells. I was quite as unable to see such a membranous septum and a mem- brane on nuclei generally, and the division appeared to me to take place by gradual constriction. According to Hofineister's descrip- tion (" Enstehung des Embryo/' 7) the membrane of the nucleus dissolves, but its substance remains in the midst of the cell ; a mass of gi'-anular mucilage accumulates around it ; this parfcs, without being invested" by a membrane, into two masses, and these afterwards become clothed with membranes and appear as two secondary nuclei (toGhter-herne), It is still an unsolved question how often the process of divi- sion of the nuclei can be repeated, whether it continue'^ indefi- nitely, or whether after one or more divisions it becomes extinct, and the formation of a new nucleus becomes necessary. In the spores of Anthoeeros I found a second division, for in the parent-cell of these a mass was formed, which first parted into two subdivisions, and then each of these divided into two nuclei. Wimmel found the same in the development of pollen-grains (" Zur EnUvhchelungs- gesch d, Pollensf' — Bot Zeit, 1850, 22o). In these cases, there- fore, a twofold division occurred. But, according to Wimmel, the case is different in the formation of the parent-cell itself, for when one of these cells is about to divide, a new nucleus is formed in it, which becomes divided and gives rise to the development of two secondary cells. When one of these secondary cells is to be divided again, its nucleus takes no part in it but becomes absorbed, a new nucleus being formed which divides, &c., so that here each nucleus is capable only of one division. The number of nuclei that are formed in a cell varies very much ; in most cases there are two, as in the formation of paren- chymatous cells in the bark and the pith, in the formation of vfood-cells in the cambium ; but in elongated cells, particularly in hairs which become articulated, half a dozen or more nuclei are often found lying in a row. In like manner varies the proportion of the size of the nucleus to the cavity of the cell j in the paren- diymatous cells of wood, in the cells of bark, and of the suberous layer of the Dicotyledons, I found the micleus relatively very small ; but in the hairs, in the cells of very small organs still con- tained within the bud, as in the young leaves, in the cells of the apex of the root, in which organs the cells divide while they aie still very small, the nuclei occupy a very considerable portion of the cavity of the cell. The formation of nuclei is soon followed by that of septa be- tween eyery two of the former, which is effected by the primor- dial utricle becoming folded inwards m the same manner as de- scribed above of Conferva glomeTuta, till a partition is formed reaching to the centre of the cell, and hy the deposition of cellulose THE VEGETABLE CELL. membranes on the outside of the primordial utricles during this process, wHch membranes form secondary layers to the parent- cell where in contact with its walls, and laminse of a partition dividing the parent-cell where in contact at the point of junction of the two secondary cells. The number and direction of their septa depend altogether on the number and position of the nuclei, since each of these becomes the centre of a secondary cell. The secondary cells accurately fill the cavity of the parent-cell, so that there is no trace of inter-cellular passages running between them, and the entire contents of the parent-cell are taken into the cavi- ties of the secondary cells. Since the membrane of the secondary cells deposited during the formation of the partition is immeasurably thin, wliile the membrane of the parent-cell usually possesses, before the division, a perceptible, often considerable, thickness, we naturally find, on examining a cellular tissue shortly after the division of the cells (fig 48), a very considerable difference in the thickness of the dif- Fig. 48 External layers of the rmd of Cereus peruv2anus —a;, cells of the rmd witli contracted pnmor- dul utricles contracted, m part contammg' newly formed septa (e) 0, Cork-cells , 5, the outer layers of tlie nnd-cells, newly-formed by the division of the latter , c, cells of the epidennig ; d, ctiticle. ferent sides of the cells composing it, for some of the walls consist of the blended membranes of the secondary cells, others of these united to the membranes of the parent-cells. This condition is in a high degree striking in the investigation of many organs in V'hich the development has just begun, 6.g., in the formation of a periderm in the outer cells of the bark, where most of the newly- formed and thin septa run parallel with the epidermis; in cam- 56 ANATOMY AND PHYSIOLOGY OF biuin, where the septa Ke parallel with the bark; in jointed hairs, &c. When the secondary cells exhibit no more, or but very little growth, this condition of the thickness of the walls is permanent, and it is possible, when the membranes of the secondary cells have been thickened by the deposition of layers, to distinguish their membranes clearly, in their whole course, from the mem- brane of the parent-cell, e,g.^ in the pith of Taxodium distichum. On the other hand, when, as is usually the case, the secondary cells increase much in si2:e after their production, this condition is changed. In these cases the membrane of the parent-cell must naturally share in the expansion of the secondary cells, and be- come thinner in proportion to this expansion ; in consequence of this the membrane of the parent-cell mostly vanishes completely from the eye, especially when the division and with it the expan- sion of the secondary ceUs is repeated. It has already been observed that the secondary cells completely fill the cavity of the parent-cell at their first origin. Thus, no traces of intercellular passages can be found in tissues in the first stages of their development. The passages are formed subsequently by the separation of the ceU-membranes at the angles of the cells, and are not, as is usually represented, the remains of free open spaces between globular cells which have been compressed together in consequence of growth. In Hke manner the stomatal pores are produced by the separation of two cells formed by the divi- sion of a parent-celL Ohserv. That the formation of ceUti in all the organs of plants (ex- cepting the cells originatiag in the embryo-sac) depends npon the division of older cells, an opinion which could not, for a long time past, "be op- posed by any carefol observer, unless he were misled by preconceived notions. Even Meyen (" Physiologiej" ii. 334) declares this process of ceU- formation to be very general; but linger {" Zinnma,'' 1841, 402; ^^ Bot Zeit^' 1844, 489), who subsequently apphed to this process the term me- rismatic cell-formation; andlsTageh (^' Zeitschr. f. wiss.Bot.^' iii. 49, 1846), who used the expression pa/rietal cell-formation^ more especially asserted the general occurrence of this process of formation ; the former declaring to be the usual mode, the latter ascribing to it the production of all vege- tative cells. But circumstances occurring iu the division of the cells were inter- preted in a different way from what I have done. Meyen assumed that the cell-membrane itself became folded inwards, and in this way formed the partition, which is decidedly incorrect. linger thought the septum to be origiaally simple, splitting afterwards into two lameUse ; NageH denied tbat the septum is formed gradually from without inwards, assuming that the membrane of the secondary cell is formed simultaneously all round its cavity, whence it would of course result, that the septum composed of the membranes of two contiguous secondary cells would be formed at once across through the cavity of the parent-ceh. In reference to tMs latter point, I, of course, readily admit that one seldom succeeds ia observing the gradual development of the septiun in THE VEGETABLE CELL. 57 consequence of the folding inward of tlie primordial utiicle, but in par- ticular cases I have seen this process most distinctly. The description giyen above rests chiefly on observations which I instituted npon the parent-cells of pollen-grains, and in the cells which separate from each other in the pore-cells of stomates. Mirbel (" Eecherches bur U MarcJmn- tia") detected, in 1833, that the parent-cells of the pollen-grains divide by septa which grow from without inward ; but the correctness of this statement was denied by Nageli {'' Untwickelungsgesch. d. Pollens^' 1849), who asserted that secondary cells (which he called special parent-cells) were formed in the interior of the parent-cells, and that the seeming septa were nothing else than the coherent walls of these cells, which were not formed in the direction from without inwards, but simultaneously all over the contents,— a view which was shared also by Hofmeister (" Entw. d. Polleoisr — Bot Zeit. 1848, 654). That these representations are incorrect, and that the septa grow from without inwards {see pi. 1, fig. 8 — 11, which represent different stages of development of the parent-cells of the pollen-grain of Althoea rosea), was akeady stated by linger (" Ueb meris- matisch, Zellenbild^mg hei der Entwick. der Follenhorperr — " Bericht. der Ver. der NaturforscK zu Gratz.^'), and no doubt remained in my mind, since I succeeded in bursting parent-cells of pollen-grains, the septa of which were but half-formed, and pressing free the primoidial utricle (pi. 1, ^g. 10), which was half constricted by folds passing inwards, into foxir globular subdivisions connected together into a common cavity in the centre. I have elsewhere (" Veron. Schrift,^^ 2d2) sought to demonstrate that in like manner in the formation of stomates, there is no production of secondary cells in the parent-cell, with an intercellular space runnhig between them, as Nageli states. The observations of Henfrey (" Annals of IF at. History y' vol. xviii, 364) are in exact accordance with mine. Of course one does not succeed in the vast majority of cases of the examina- tion of a tissue where the celL are in course of development, in observing the gradual growth of the septa from without inwards, and when I as- sume that this process occurs universally, I certainly rest upon the analogy to the fe^ case^ m wMch I have traced their gradual de^lopmeat , bft it seems to me more logically correct to lay the main stress upon a few accurately investigated cases, than to disregard such observations, and to use as the basis of the theory of the development of cells, the imperfect, though numerous, observations in which the gradual growing in of the septum was not seen, but the mode in which it really was formed was not perceived at all. h. Free Cell-formation* In free cell-formation, the cell-membrane is developed over the surface of a mass of nitrogenous substance swimming in a fluid which contains formative matter, without the co-operation of a parent-cell. In the regular course of vegetation this process of cell-formation occurs only in the interior of cells ; it may occur independently of the life of the parent plant in the creation of parasitic Fungi, Yeast cells, &c., both in the decomposing fluid of cells and in the excreted or expressed juices. In normal free cell- formation the secondary cells usually possess but a very small size 58 ANATOMY AND PHYSIOLOGY OF in comparison -with tlie parent-cell, and stand in no connexion, or, at leastj not a necessary one, with the walls of the latter. In the Phanerogamia, free cell-formation occurs only in the embryo-sac, in which both the rudiment of the embryo (the em- bryonal vesicle) and the cells of the endosperm originate in this way ; in the Cryptogamia it occnrs only in the formation of spores in the Lichens, and some of the Algse and Fungi. The formation of free cells is usually preceded by the produc- tion of nuclei. In this case more or less abundant accumulation of protoplasm in the parent-cell forms the first sign of the second- ary cells. This sometimes fills up the cavity of the parent- cell, e. ^ , in the parent-cells of the spores of the Lichens, Pezizm, &c., sometimes it occurs in relatively small quantity under the form of cloudy masses not sharply defined, and of currents, as is usual in the embryo-sac (pi 1, fig. 12, s). In this protoplasm are formed isolated points of concentration in the form of more or less trans- parent nuclei, around which accumulates ayariable portion of the burrounding protoplasm, originally exhibiting no decided outline, subsequently clearly defined by the formation of a primordial utricle over the surface, which is rapidly followed by the produc- tion of a cellulose membrane enclosing the whole nitrogenous contents (pi. 1, figs. 13, h ; 14, h), Ohsem. To Schleiden belongs the merit of dibcovermg free cell-formatioii and the depeadaiice in which the origin of a cell stands to the formation of a nucleus ; but he was led by this discovery to the misconception that this was the only mode of formation of the cell occxuTing in natiu*e. In accordance with thib hypothesis, the cells which were formed in other cells would always be much smaller than the parent-cells, and would gradually expand imtil they filled up the cavity of the parent-cells, and their walls came into contact. But as the whole process could not take place in cells which contain granular structures, such as chlorophyll or starch gra- nules, or the like, without the displacement of these structiu'es, and yet in a cell of that kind in which division occurs, all these structures are still present after the division, Schleiden invented an hypothesis to explain the ckcmnstance, namely, that these structures in the cavity of the parent- cell were dissolved outside the secondary ceU, and formed a-new inside it. But as nothing of this process can be observed hi nature, it alone suffices to refute the doctx'me of the universality of free cell-formation. Even when quite recently, in consequence of Nagelfs observations, Schleiden {"Grundz." 3rd ed. i. 213) can no longer deny that a division of cells does occur, still he is far from acknowledging the universal diffiision of this process, since he only refers to the older notion, retracted by Hkgeli himself, that this mode of formation occurs in the Pbanerogamia or in the special parent-cells of the pollen-grains, and altogether ignores the fact that llTageh and others have shewn this to be the mode of formation of all cells except those originating in the embryo-sac; consequently, Schleiden still ascribes to free cell-formation an influence on the develop- ment of the plant which by no means belongs to it. When he states that the cells are developed in this way in the embiyonal vesicle, this is THE VEGETABLE CELL. 59 cl&cidcdly false, foi^ all recent observations agree in diewing tliat the em- biyo originates from the germinal vesicle by cell-division ; not less incor- rect is it, that free cell-formation may be traced in jointed hairs, and just as little does it accord with the mode of formation of other plants that, as is stated (^' Grundz.'' L 211), cells are formed in cells, and the parent-cells absorbed, hi the i)oints of the roots and shoots of the stem of Gypri^n- cl'mm. The entire representation proves that Sclileiden has never once observed the division of a cell. The first account given by Sclileiden (" Beitr. zur Fhytogenesis^ MuUer's Archive 1818) of the process of cell-formation, was faulty m many re- spects. He altogether overlooked the important ckcumstance that the nitrogenous substances were the originators of the formation of the nuclei and the cell, for he believed the granules of protoplasm, which he denominated mucilage {schhim)^ to be identical with the granules of gum, and thought that the protoplasm might be replaced by starch, and go through similar metamorphoses ; for he expressly mentions that starch, or the granular mucilage replacing it, is present in the pollen-tubes, but those substances are soon dissolved or change into sugar or gum. In the formation of a nucleus those httle mucilaguious granules were produced in the protoplasm, then a few larger granules, and soon afterwards the nuclei shewed themselves. When a cell was foimed, it had at first the form of a segment of a sphere, the plane side formed by the cytoblast, the convex side by the cell-membrane. Originally the cell-membrane was soluble in water, but it soon expanded more and more, and acquired greater consistence ; and its walls, with the exception of the cytoblast, which always foi-med part of the wall, were composed of gelatine. The cell now bOon became so large that the cjrfcoblast appeared oiiLy as a little body enclosed in the lateral wall. The cytoblast might go through the whole vital process with a cell, if it were not dissolved and absorbed in cells des- trued to higher development, either in its place or affcer it has been cast off like an useless member, in the cavity of the cell. — The whole of this account of the relation of the nucleus to the cell-membrane is incorrect. The nucleus is not connected with the cell-membrane under any circum- stances, for it is enclosed, with all the rest of the contents of the cell, in the piimordial utricle. Its position in the newly originatiug cell is, as appearb to me, always central, and its form mostly globular ^ it does cer- tainly often lie upon the wall of the cell subsequently, and becomes fiat- tened. The distinction which iJTageli tries to carry out between central and parietal nuclei is not founded in nature. In Schleiden's more recent writings the above views are partially modi- fied. It has been recognized that the supposed gum is a nitrogenous substance, but the name mucilage (schleim) has been retained ; and it is stated of the young cell, that in many cases, after one side of it had become elevated like a vesicle from the surface of the nucleus, a second layer is deposited upon the free side of the latter, protecting it from solution ; the special statement that all cells are formed in this way is more and more extended to aU organs of plants, even to the cambium-layer of the Dico- tyledons (" Anatomie der Cacteen,'' 35). Although it is a rule, which has no exception in the normal development of the cells of all the higher plants, that nuclei make their appearance in the nitrogenous substances which give rise to 60 ANATOMY AND PHYSIOLOGY OF the formation of a free cell, yet tliis is not a necessary condition, for it appears tliat every globular mass wholly or partly composed of proteine compounds is capable of undertaking the fiinction of a nucleus, clothing itself with a membrane, and thus producing a cell. This state of things is of very frequent occurrence in the formation of the spores of the Algse, where the whole contents of an entire cell, e. g., in Vaucheria, of two copulated cells, e. g,^ in Zygnema, become balled together into a globular mass, and coated by a membrane. But it is not always such large masses, com- posed of starch and chlorophyll granules and protoplasm, which give rise to the formation of a spore ; in very many cases smaller globular masses of the green contents, produced by the union of a a few chlorophyll granules, and undoubtedly also single granules of chlorophyll, may assume this function whence Kiitzing called the granules lying in the cells of Algae — gonidia. This occurs in the most striking manner in Hydrodictyon, in every cell of which the sporidia produced from chlorophyll granules arrange them- selves in a net-work over the whole of the inner surface of the parent-cell, become converted into cells which grow together at their angles, and thus collectively form a new plant. Pollen-grains and the spores of the higher Cryptogamia exhibit a peculiar mode of formation which conuects the division of cells with free cell-foimation. After the development of four nuclei, produced by the division of a single nucleus, accompanied simul- taneously by the absorption of that nucleus which had given origin to the parent-cell, the latter becomes divided into four compart- ments (Nageli's special parent-cells) by the folding inward of its primordial utricle and the gradual formation of septa (which are four or six in number, according to the relative position of the nuclei, or, it is first divided into two segments, which are again divided into two chambers (Nageli's special parent-cells of the second degree). These secondary cells are adherent to the wall of the parent-cell wherever in contact with it, therefore up to this epoch only the common process of cell-division occurs (pi. 1, figs 8, 9:, 11). But the contents of each one of these four subdivisions now become clothed by a new membrane (the inner pollen or spore- coat), which, although in accurate apposition with the membrane of the cell in the cavity of which it lies, does not adhere to it, and subsequently secretes the outer pollen- or spore-coat. The forma- tion of this inner pollen-cell only resembles free cell-formation in tlie circumstance that its membrane is produced in the cavity of another cell, around a primordial utricle which contains a nucleus, without adhering to the parent-cell and forming one of its secon- dary layers ; it is distiDguished from free cell-formation by the fact that the nucleus and the primordial utricle around which the new cell-coat is produced, belonged previously to the parent-cell, and had caused the origin of this itself, and had not been newly- formed for the secondary cell. THE VEGETABLE CELL. 61 II. THE PHYSIOLOGICAL CONDITIONS OF THE CELL. Even as in anatomical respects the cell appears, on tlie one hand as an independent organism, self-contained, and following its own proper laws of formation in its development, and again, on the other hand, in the great majority of plants, does not appear iso- lated, but forming part of a greater whole, with which it is not merely mechanically connected, but by the influence of which its organic development is modified, so that its form, the position of its pits, &c., are dependant on the condition of the neighbouring cells, — so, in like manner, is the physiological activity of the cell, on one hand independent of, and on the other dependant on, and ruled by, the vital activity of the entire plant. The vital functions of plants are separable into two great classes, into those of nutrition and those of propagation. Both are committed to the cells. The share which the individual cell takes in one or both of these functions varies extremely according to the degree of elevation of the organization of the plant. In the lowest plants, whether, as in Protococcws^ they consist of a single cell, or as in the Confervas of rows of cells united into a thread, each cell is capable of an independent existence. It ab- sorbs fluid from the surrounding medium, respires, assimilates the absorbed substances, &c. ; in short, the simple vesicle suffices for the accomplishment of all the various functions which must co- operate in the nutritive processes of the plant. The more highly organized a plant is, the more these various functions are com- mitted to particular organs, the offices of which in this way be- come special and one-sided, thus being reduced to a dependance on the functions of the other organs. The function of absorption is committed to the root ; that of breathing and the elaboration of the absorbed substances to the cells of the leaf, &c. With the combination of many cells into a whole, leading a common life, comes the necessity of a passage of the sap from one organ to another, a circulation of the fluids, which the simply formed plant can wholly dispense with. This movement of the sap is in great part committed to particular cells, which take but a subordinate part in the real business of nutrition. Analogous to the more independent condition of the ceU. as an organ of nutrition, in proportion as the organization of a plant is simpler, the greater is its activity as an organ of propagation. In the lowest plants the same cell is an organ of vegetation in the earlier period, and an organ of fructification in the later period of its life, germinal granules (keim-kdmer) being formed in its in- terior. In the higher plants, on the contrary, these two functions are committed to different cells, in which case, at first, as in the 62 ANATOMY AND PHYSIOLOGY OF Lichens, all the oi^gans of finctification are ahke, while in the moie highly developed plants a contrast between these appears, a male and female sex, the conjunction of which is necessary for the origin of a new plant. Thus, the more complicated the structure of the entire plant becomes, the more manifold the vital phenomena of the whole display themselves, the more do we see the functions of the fun- damental organs of the vegetable become restricted to an activity continually becoming more special. The question here presents itself: In what connexion does the more manifold or more special activity of the cells stand with their organization ? To this ques- tion we have no answer. The organization of cells, the substances of which their membranes are composed, are so iiniform through- out the whole vegetable kingdom, and all the organs of the par- ticular plant, that as yet the connexion which must exist between the form and organization, and the function of the cell, is alto- e^ether unknown. The function of nutrition and that of propagation form a strik- ing contrast in all the cases in which the propagation is by spores and seeds, since the reproduction in these, through the germination of an organ furnishing a new plant, always causes the death of the organ of propagation, and in many eases of the whole plant. But there is another kind of multiplication ; the propagation by buds, which dependb on the common laws of growth, and has its origin in the organs of vegetation. This mode of increase is based on the peculiar growth of the plant. Leaving out of view the simplest forms of the vegetable kingdom, the plant does not consist of a fixed number of organs, developed together and at- taining the full-growth at the same time, so as to form a com- pleted whole, and to suffer a common death ; but the organs of the plant are developed successively in an unlimited series ; every fresh shoot has the strength of youth, and is capable, under fa- vourable circumstances, of entering on an independent life sepa- rately from the other parts, and of growing into a new plant. When even all the parts of a plant do lead a common life, they do not collectively form one individual, but separate individuals growing out of each other, and blended together in consequence of theix growth. It depends on the degree of organization of a plant what part we are to regard as a special individual. When an uni-cellular plant divides into two ceUs we must regard each cell as an individual, e, g., in the Diatomeae ; in the Thallophy tes, for instance in the Lichens, each lobe of the thallus can carry on an independent life when separated from the rest of the plant ; in the higher plants each branch forms a repetition of the stem which grew from the seed, and a ramified plant is looked upon as a col- lection of as many individuals as there are branches upon it. In this manner a branched plant (when not exhausted by the pro- duction of seed) is ever young in its fresh shoots, although one THE VEGETABLE CELL. 63 part after another grows old and dies ; new, active individuals sprout annually from the old ones, and there is no natural termi- nation to the life of the whole. At the same time, the possibility is given for a plant, in consequence of this unceasing production of shoots, to become separated into an unlimited number of dis- tinct plants, in a natural way by spontaneous, or by artificial, divi- sion. From this peculiarity of the unlimited growth of a shoot has the German language derived the expressive terms gewachs (a vegetable, from wachsen to grow). Observ. The peculiarity of their organization, and the unlimited power of growth of plants, offer many difficulties to the definition of the Jiu-a- tion of plants, and have given rise to many incorrect theories. Every individual cell, and every individual organ has a determinate end to its life, but the entire plant has not, since the individual shoots run through theh^ periods of development quite independentily, and only share in the weakness of age of the older organs when these are no longer able to convey to the young shoots the needM amount of nourishment, in which case the latter do not die from deficiency of vital energy, but are starved. It therefore depends wholly upon the mode of growth of a plant whether this occurs or not. When a plant possesses a thallus spreadmg horizon- tally by the growth of its circumference, it can annually extend itself into a larger circle, after the old parts in the centre have been long de- cayed, as is seen in old specimens of crustaceous Lichens, in the fahy rings caused by Fungi, &c. In like manner when a higher plant has a creeping stem, and possesses the power of sending out lateral roots near the vegetating points, and in this way conveys nourishment directly to the young terminal shoots, the latter are wholly independent of the death of the older parts of the stem and of the primary roots, and there exists no internal cause for death in such a plant. It is truly a different plant every new year and vegetates in a new place, but there is no definite boundary between it and its predecessors j such a plant is like a wave rollmg over the surface of a sheet of water, it is every moment another, and yet always the same. Thousands of inconspicuous plants, of Mosses, Grasses, Hushes, &c., have vegetated hi this maimer upon peat bogs and similar localities perhaps for thousands of years. Plants with upright stems are placed in much more unfavourable circumstances. It has been declared of these also, and particularly of the Dicotyledonous trees (Be Candolle, " PJiysiologie Vegetate^ ii. 984), that they have no internal cause for death, but I behove incorrectly. Examples of very old trees, such as De OandoUe collected (e. ^., Taxus 3000, Adansonia 5000, Taxodmm 6000 years old, &c.), only prove, naturally, tliat death occurs at a very late period in many plants placed in favourable circumstances, but not that it does not necessarily happen. To me there appears to exist in all trees, whether they belong to the Dicotyledons, or, hke the Palms, to the Monocotyledons, an internal cause which must produce death in time — namely, the increasing difficulty of conveying the necessary quantity of nourishment to the vegetating point, resulting from the elongation of the trunk from year to year. Even when the force which carries the sap up suffices to raise it to 200 feet or more (many Palms, as Geroxylon cmdieola^ Areca ohrmea^ ^ttdiksx a height of 150 — 180 feet; some Goniferse, 6, ^., Qi ANATOMY AND PHYSIOLOGY OF Fmus Zamhertiij Abies Dauglmii, of more tliaii 200 feefc)^ yet a maximum is reached tliere, and the terminal shoot is less perfectly nourished every succeeding year^ becomes stunted more and more, and the tree at length dies. Thousands of experiments have shewn that the young shoots of old treesj when used as grafts, slips, tance should have been abBorbed, instead of which Polygonum Fersicaria absorbed of, — Chloride of Potasbum . . „ Sodium , * . Nitrate of Lime .... Sulphate of Lime . . . Chloride of Ammonium Acetate of Lime . . Sulphate of Copper , . . Gum ... ... Sa^ussure tried to explain these differences in the absorption from phy- sical differences in the solutions, especially by the assumption that the quantity of substance absorbed, depended on the greater or less degree of viscidity which it imparted to the water by its solution. He regarded, namely, the cell-membrane as a very fine filter, through which not only would a denser solution penetrate more slowly, but which was also ca- pable of separating the solution into a more concentrated and a more diluted one. This explanation is certainly not sufficient, since we have no proof that the finest filter can effect such a separation of a fluid ; and secondly, Triiichiiietti found that the quantity of substances taken up by i^oots did not run parallel with the viscidity of their solutions. But there is nothing in the result of these experiments which would be in opposi- tion to the laws of endosmose, in particular the separation into a thinner and a denser fluid btand in agreement with these, since many observations (of Jenchau, Brucke) have shewn, that in endosmose the fluid does not necessarily penetrate the septum in toto, but that in many cases a dilute fluid or merely water goes through. "We are certainly not in a condition to state at present how one salt passes over in this, another in that, quan- tity ; to do this it would be necessary to know the contents of the vege- table cells and the relation in which they stand to the cell-membrane and to the different solutions ; but no contradiction exists between the phe- nomena referred to and endosmose. Formerly it might have been con- cluded from the different behaviour of diseased and healthy roots, that absorption was not a true physical process, but that the force of the living plant was to be considered in reference to it ; but not to speak of the above-noticed contradiction that a vital act would be exalted in a dead cell, there occur in the disease and death of a cell, two alterations which cannot be without influence on the endosmose. In the first place the living cell exhibits a certain tension, which is lost in the dead cell; in the second place the primordial utricle is very readily detached from the inside of the cell-wall m diseased or dead cells ; these two circumstances place the cell-wall in a condition essentially different from the normal one, and we may readily conceive that the endosmotic force of the cell- wall becomes essentially different, and that the dead cell-membrane is penetrated much more easily and quickly than the wall of the living cell. There are frequent opportunities of observing the more easy penetration of a diseased or dead cell, in microscopic investigations where tincture of iodine is applied ; for, in the Oonfervce. for example, where several cells r 2 68 AHATOMY ANB PHYSIOLOGY OF lie near together, some healthy, others diseased, the latter are very imioh more quickly penetrated by the tincture of iodine. An important question in absorption is this : are the different substances absorbed by different plants in equal relative quan- tity, or does one plant take up one substance, another a second in greater abundance? Saussure, who thought the latter condi- tion not improbable, could not find any confirmation of it in his experiments, for the variations which'^he found in the absorp- tion of different substances by different plants, were not more con- siderable than the variations which occurred in different experi- ments with the same plant. Trinchinetti (Sulla facolta assorhente delle radici) made experiments on this question, by ])lacing differ- ent species of plants in mixtures of two salts which do not decom- pose one another, whereby he shewed that certainly one plant ab- sorbed one, another plant the otlier salt, in preference, from a mix- ture of nitrate of potass and common salt. Thus Mercurialis annua and Qhenopodium mride absorbed much nitre and little salt, while Satureia hortensis and Solanum Lycosijersicum took up much salt and little nitre, and from a mixture of sal-ammoniac and salt Mereurialis absorbed more sal-ammoniac, while Vicia Fa a took more salt. If, however, as there is every appearance, the result obtained by Trinchinetti be correct, we can by no means deduce from it the con- clusion that the plant possesses the power of absorbing substances useful to it and excluding those Avhich are injurious, for experi- ence has amply demonstrated that it does not possess this latter power, that it can even, m Saussure's experiments with sulpliate of copper shew, absorb injurious substances more easily than those which it applies to its nutrition, and we must assume that the cause of the differences in question is to be sought in the physical and chemical peculiarities of the particular substances, and their relation to the cell-membrane and the cell-contents. ^ Observ, It is a known fact that different species of plants which grow side by side in the same soil, to the roots of which the same nutriment is conveyed, shew by analysis of their ashes a very different composition of fixed constituents derived from the soil This circumstance may be ex- plained in two ways; either through the assumption tliat different species of plants take up different constitvients in unequal quantity from the same solution, for which the experiments of Trinchinetti above-mentioned furnish positive evidence, or through the hypothesis defended by Liebig, that different plants take up equally, like a sponge, all that is dissolved in water, hut again reject all superfluous or injurious substances. The first must be regarded as hj far the more probable in the present state of our knowledge, since the second hypothesis, which is based upon Macaire- Princep's experiments, presently to he mentioned, that substances imfit for the plant can be again excreted by the roots, has not been confirmed by later researches. It is certainly not to be denied that plants possess in the fall of the leaves a means of removing a part of the substances THE VEGETABLE CELL. 69 taken up by tlieir roots, but tbis means can only act in perennial plants, and not in annuals. Since tbe roots undoubtedly possess tbe power of separating a saline solution into a dilute and a concentrated, and absorbing tbe thinner ; and since, according to TrincMnetti's experiments, certain plants absorb par- ticular salts oidy in very small quantity^, tbe question arises wbetber, in particular cases, tbe plants are in a condition to take up from a solution water alone, witb tbe total exclusion of tbe dissolved substance. We Lave no definite experience on tbis point, but sucb a thing is not impro- bable. I may mention bere tbat formation of Pungi lias been observed even in arsenical solutions, for arsenic is a substance so hostile to vege- table life, tbat it can scarcely be supposed tbat any plant could maintain its existence when it contamed arsenic in its sap. It was also observed hj Yogel (-Erdman and Marcliand. ''Journ,,'' Bd. 25, 209), tbat Cereus variabilis bad taken up no copper after having been watered for ten weeks with solution of sulphate of copper, that the copper penetrated just as little into the leaves of Stratiotes ahides, and that Chara vulgaris vegetated for three weeks ui a solution of sulphate of copper without taking up this metal. If the experiments mentioned in the foregoing cannot be ex- plained in every single detail through the laws of endosmose, yet there is a great probability that this will be possible in time. "We must not forget, in considering this absorption, that in the majority of plants we have to do with an apparatus in wliich the laws of endosmose cannot display themselves clearly. These can only be seen undisturbed v/here no other force is acting upon the two fluids separated by a partition. But only the comparatively few plants growing totally under water occur in this condition, while the physical conditions in which the great majority of plants are placed, must give rise to impoitant modifications in those of their phenomena depending upon endosmose. Since the leaves have a large surface with a comparatively small mass, and are provided with numerous stomates on the under side, they are fitted to evaporate a great quantity of water. This does occur in a surprising degree when external circumstances do not repress the foi*mation of vapour; thus, for example;, in Hales' experi- ments, a sun-flower 8| feet high lost on an average a pound and four ounces of water daily in this way, the loss rising to a pound and fourteen ounces on a warm and dry day, from which Hales reckoned that in comparison of the surfaces, the evaporation was some three times as strong in this plant as in man, and in comparison of volume seventeen times as strong. So consider- able a loss of water cannot remain without re-action upon the absorption of the root-cells. For since the sap in the cells of the leaves becomes so much more concentrated through the loss of water, their power of inducing endosmose will increase in propor- tion, they replace the water taken from them, from the cells of the stem, and so tliis action is continued through the whole tissue of the plant down to the i-oots, which strive to absorb water from 70 ANATOMY AND PHYSlOLOGr OF witlioutj in the same proportion as it is evaporated from the leaves. A proof that the evaporation of the leaf actually in- creases the absorption, is again furnished by the experiments of Hales, according to which the quantity of water that a shoot ab- sorbs is in direct proportion to the number of its leaves, and the quantity of water absorbed sinks to one half when half the leaves are cut off the shoot ; the experience also speaks in favour of it, that during winter the root of a plant standing in the open air, for instance, a vine or a hazel bush, begins to absorb if one of its shoots is introduced into a hot-house, and the unfolding of its leaves caused by the action of heat. Liebig (" Researches on the Movement of the Juices in theAnimctl Organism/' Untersiick hher Safibewegung^ cfcc, 68) has also shewn the influence wliieh is exerted by evaporation at one point even in apparatus artifi- cially contrived, and which, when it is assisted by the pressure of the atmosphere, is capable of causing the fluid to flow through the membrane against the laws of endosmose. In plants, this in- fluence not only suffices to increase the absorption, and cause it to commence under circumstances in which it did not otherwise occur, but is even powerful enough in plants which have been poisoned, to carry the poisoned fluid in great abundance upward through the already dead lower part of the plant. Ohserv, I hei^e refer to experiments "wMch I have made both on Firs and Dicotyledonous trees in regard to the absorption of pyrohgnite of iron, the diffusion of which through the plant is readily perceived by the dax'k colour. Young trees sawn off and placed with the cut surface in the fluid, became filled with it, when they had white wood like the Bnch, in all their parts from below upwards, and continued to convey the fluid upwards in this way through the lower part of the stem, after all their ceils were saturated with it and their cell-membranes were infiltrated with it through their entire thickness : under which circumstances we can certainly not imagine them to have retained a remnant of vitahty. a. Diffusion of the Sap in the Plant The mode in which the fluid taken up by the cells situated at the surface of the rind of the root becomes diffused in the plant, is a subject which lies in far deeper obscurity than the absorption of the cells in contact with watery nutriment In the lower 'plants which are composed of single cells, as Protococcus, there can be no movement of the sap, and even in such as are com- posed of simple rows of cells, like the Confervas, each cell seems to elaborate independently the nutriment it takes up. In the Lichens we have already an indication in the different structure, and especially in the green colour of the internal layer, that here, where indeed no distinct organs exist, the different layers of the thalius are endowed with unlike physiological functions ; we can scarcely imagine this without an exchange of the juices of the THE VEGETABLE CELL. 71 different layers, without a movement of the Rap ; but we are wholly ignorant of all that relates to this. The case is differeDt with the Phanerogamiaj in which the different processes connected with the nutrition are committed to different organs ; here we at least know somewhat more accurately the course which the sap describes, at all events in the Dicotyledons A few simple experiments leave no doubt about this. The watery fluids are, as we have seen, absorbed by the cells lying at the surface of the rind of the root, they flow no further, however, in the rind, but pass into the wood, even in the small roots, and ascend in this through the stem and branches. The proof of this is fm^nished by two facts : if the bark of a plant, best of a tree, is cut tln'ough in a ring down to the wood, there is no interrup- tion of the flow of sap to parts situated above the wound ; but if the wood is cut through, the greatest care being taken to avoid injuring the bark, that portion of the plant above the wound dries up at once. From the wood of the stem and branches the sap flows onwards into the leaves, and in these into their paren- chymatous tissues, as is proved by the powerful expiration of Water vapour from them. Before the sap has reached the leaves it is incapable of being applied to the nutrition ; conseq^uently, the vegetation of a plant comes to a stand still when it is de- prived of its leaves. The sap ascending from the root to the leaves is thence termed the crude sap. It undergoes a chemical change in the leaves, rendering it fit to be applied to the nutrition of the plant. To this end the sap flows backwards from the leaves through the bark, to the lower parts, as the following cir- cumstances testify. If the bark is cut off the stem in a ring, the grbwth of that portion of the plant below the wound stands as it were still, the stem becomes no thicker, in the Potato plant no tubers are produced, &c. ; but on the other hand, the growth above the wound is increased beyond the usual measure, very tliick layers of wood are deposited, more fruit is perfected, these ripen sooner, &a The deposition of starch which occurs in the cells of the medallary rays in Autumn, goes to prove that the portion of assimilated sap which is not used for nutrition on the way to the root, runs back to the wood through these horizontal medullary rays, and thxis the sap describes a kind of circle, not, indeed, in determinate vessels, but in a definite path leading through the different parts of the plant. Observ, It is difficult to conceive how in recent times the results of these experiments (for the details of which reference should he made espe- cially to Buhamefs ^^ Physique des arhres'^ and Cottars ^^ N aturheohmh- twhgen uh. d. Bewegung des Sa/ies") could have been questioned, and the existence of the descendmg current of sap in the hark denied. Certainly it is no improvement on the theory cast aside, when the increased growth above the annular wound is explained by artificial interruption of the upward current of crude sap, in consequence of which the sap coutaiaecj 72 ANATOMY AND PHYSIOLOGY OF in the upper part of tlie plant, must soon become greatly concentrated and potential for development (Sclileiden, " Gruiich.'' 2iii(l ed. II. 513). Wlien we can succeed in fattening an animal by depriving it of a portion of its accubtomed food, t3ii& explanation may be received as satisfactory. Mulder bIbo {" Fh^siolog, Ohem.'") denies tliat iliere exists a downward current of tlie sap, aitbougli lie does not call in question the fact that the nutrient matters formed in the leaves do descend. That is to say, he assumes that the substances which the sap carries upwards are exchanged, according to the laws of endosmobo acting in the ascending sap, with those substances which are elaborated in the leaves. If this were the case, the latter nutrient matters must descend in the same coiu'se and through the very cells in which the sap ascends, i e., through the wood; the above- mentioned experiments demonstrate that they certainly do not, but remain in the upper parts of the plant when this path is freely open to them. The diiferont layers of the wood do not convey the sap in ^qnal quantity ; the outermost, youngest layers, and in stems not more than two years old also the mea"allary sheath, principally preside over the conveyance of the sap. The older a tree becomes, and the harder the wood it possesses, the less share do the older layers take in the conveyance of sap ; hence, trees with hard wood, like the Oak, where the sap wood exists in a circle round the stem, dry rapidly; while in trees with soft wood, like the Bii'ch, the central layers of wood still carry sap, even in thick trunks. When the question arises as to which elementary organs the sap ascends in, and by what force it is lifted upwards, we arrive at a region wherein a]i is still obscure, but in which so many the more hypotheses have been ventured. In the first place, two views stand diametrically opposed to each other ; according to one, the conveyance of the sap is committed to the vessels ; according to the other, these ca^ry air, and the sap flows in the cellular tissue. The adherents of the first opinion (to which belonged Malpighi, Duhamel, Treviranus, Link) chiefly de- pended upon the circumstance that when cut plants were placed in coloured fluids, these became diffused through all parts of the vascular system, a conclusion which, while referring to processes occurring in healthy plants, takes its stand on plants placed in most unnatural circumstances, and is now not considered valid by any one. In like manner, no great weight can be laid upon the phenomenon of the sap flowing from the cut vessels when trees such as the Birch, Maple, Vine, &c., are wounded in Spring; since these plants are in such diflerent conditions before the un- folding of their leaves and in later periods of their vegetation, that a conclusion from one to the other must be regarded as inadmis- sible. More important to the theory of the conveyance of the sap are the experiments of Link Q^Ann, de sc, natnr, XXIII f' 144 — - " Varies m. KrauPTku^idc" i, 116), according to which, plants which have been watered for some days with a solution of ferro ^THE VEGETABLE CELL. 73 cyanide of potassium, and afterwards with a solution of sulphate of iron, had prussian blue precipitated in the vessels and not in the wood-cells. If this result proved constant, the experiment must be acknowledged as a conclusive evidence for the conveyance of the sap by the vessels, but although these experiments were con- firmed by Eoininger (" Bot Zeit" 1843, 177), and also have been made repeatedly by myself with the same results in many other cases, with Hoffman Q'kk cle Organe d. Safibewerjung/' — Bot Zeit ISoO ; Scient Memoirs, Series 2, Vol. J.), they furnished diametri- cally opposite results, without our being able at present to deter- mine with certainty the cause of the difference, which po&sibly may have depended on accidental injmies in the plant where the saline solutions penetiated into the vessels. The defenders of the idea that the vessels carry air, as the chief of whom in recent times Schleiden is to be named (" Grundz,'' 2nd ed. II. 505), stand simply upon microscopic investigations, since in these air is always found in the vessels. This statement, special exceptions excluded, is undoubtedly correct. In the first place, in regard to these exceptions, our woody plants furnish them during the time preceding the unfolding of the leaves in Spring. During the winter a portion of the cells of the wood are filled with sap, the vascular system with air. Dur- ing the rising temperature of Spring the cells become gradually fuller and fuller of sap, and this subsequently enters the vessels also ; noA^ the sap flows freely from wounds in the wood, which is not the case so long as this is contained in the cells alone ; after- wards, when the unfolding of the leaves increases very much the evaporation of the plant, the wood is again partially emptied of its sap, and air re-enters more particulaiTy into the vessels. This condition of a special fulness of sap, in which the vessels also con- vey it, seems to be a constant condition in certain tropical climb- ing plants, especially in Phytocrene and certain species of Cissus (see Gaudichaud, " Obscrv. sur V Ascension de la s^ve dans uns Li/me f — Ann. des.sc. nat 2nd ser. VI. 138 — Poiteau, "Sur la Liane des Voyagcurs;" — Ann. des. sc. nat VII. 233), The sap is exposed to a more or less considerable pressure in the vessels, so that it mostly flows with force out of a wound ; the force with which this takes place was first determined by Hales, in his cele- brated experiments on the Vine, which afterwards were fully con- firmed by other experiments, more particularly by those of Briicke Q' Fogg Ann." 1844, No. 10). Hales found that the presence of the sap flowing out under favourable circumstances balanced a column of mercury twenty-six inches high. In the observations made by Gaudichaud on Cissus hydrophora^ and by Poiteau on an unknown Oissus, the sap did not flow free from either the upper or lower piece of the cut stem, but only out of pieces of stem which were separated completely firom the parent plants, so as to present two open ends ; here evidently the vessels were not over-filledi 74i AKATOMY AND PHYSIOLOaY OF witli sap, and this was retained in tlie cut plant by the pressure of the atmosphere. If we take into consideration that the vessels, save in the said exceptions, convey air, that in the Vine and other woody plants, before the bleeding begins, tho cells are filled with sap, which is only afterwards taken up by the vessels, that after the unfolding of the leaves and the great evaporation resulting from this, the ves- sels are again emptied of sap, we cannot doubt that the cellular tissue of the plant is the primary and principal system to which the conveyance of the sap is committed, and that the vessels take part in the function only under special circumstances, when the plant is temporarily overfilled with sap, or in some very succulent plants perhaps throughout the whole period of vegetation. All parts of the plant do not play an equally active part in the conveyance of the sap, for many experiments go to shew that the organs situated at the two ends of the plant are especially active at least in the ascent of the sap, the root fibres on the one hand driving sap upwards, and on the other hand the leaves attracting it. That the ascent of the sap in Spring, before the unfolding of the leaves, is chiefly caused by the roots driving the sap up- wards, might be partly deduced from the fact, that the force with which the sap flows from a wound in the stem of the Vine, is de- pendant on the temperature in which its roots are placed (Dassen, ^^ Froriep's Neuen Notizen^" B 39, p. 129), partly also from the fact that the sap does not flow merely from the cut stem of a bleeding Vine, but the same phenomenon is displayed in the roots down to their most slender ramifications. But that in many leafy plants, in which the attraction of the sap by the leaves is active as a second cause of the motion of the sap, the impulse exercised by the roots upon the mass of the sap is also frequently necessary, for the conveyance of a sufiicient quantity of sap to the leaves, follows from the experiments of Dassen, according to which, in N'yonphcea alba and other plants, the leaves dry up, when they, or the stems to which they belong, are placed with their cut sur- faces in water, but they remain fresh, under similar surround- ing conditions, when the fibrils of the roots are uninjured. Yet that the leaves, even when only a comparatively small number of them are left at the top of a plant, are in a condition to lift fluids to a very considerable height in the stem, independently of the influence of the root, follows from the experiments made by Boucherie (^'Gompt rendus,'' 1840, ii. 894) upon trees, in which a solution of pyrolignite of iron was applied to the lower ends of the sawn-off stems. Observations on bleeding woody plants, especially on the Vine, prove that the activity of the roots is capable of causing the sap not only to ascend in the cells of the stem, but also to enter into the vessels. In like manner the activity of the leaves causes THE VEGETABLE CELL. 75 fluids, ill which the open orifices of a cut stem dip, to ascend in its vessels. At first sight it seems very easy to give an explanation of the ascent of the sap, both before the opening of the buds at the re- commencement of vegetation, as well as during the period in which the plants are clothed with leaves. DuriDg the period of the rest of vegetation, the cells of a perennial plant are filled with a great quantity of organic compounds, under the form of proteine substances, sugar, gum, and more paiticularly of starch, which latter is converted into sugar at the re-commencement of vegeta- tion. In consequence of this, the cell-sap becomes capable of setting up a powerful endosmose, and nothing seems more natural than that the cells of the roots should absorb the water which exists around them, and that the sap diluted by this should be taken up by the cells above, and so be carried gradually up- wards from one cell to another, whence the notion that endosmose is the sole and sufficient cause of the motion of the sap, counts many adherents even in recent times. But on closer examination the matter appears less simple than it seemed at the first glance. The organic compounds, especially the starch, are not, for the most j)ai t, contained in the elongated cells of the wood, in which the sap ascends, but more particularly in the cells of the me- dullary rays and in those of the rind of the root, while in those Monocotyledons, which, like the Palms, lay up a store of sugar, gum, starch, &c., before the time of flowering, these substances are deposited in the parenchymatous cells of the stem. Thus the substances which cause the setting up of the endosmose, occur in cells which do not preside over the conveyance of the sap, while in the elongated cells of the wood, substances which would cause endosmose exist only in inconsiderable quantity, and in the ves- sels not at all. How then does the sap reach the wood -cells and vessels, and how is its motion imparted to it? I consider these questions as unsolved at present, Briicke (1. c. 204) has indeed promised to demonstrate that this process depends on the laws of endosmose, that the parenchyma- tous cells first become densely filled with water by the help of the soluble and expansible substances contained within them, and then since they continually attract water, pour out that which they cannot make room for in their cavities, with a portion of the soluble substances, as sap, into the neighbouring vessels; but Briicke has not yet furnished the demonstration of this. But even if we would assume such an excretion from the cells causing the endosmose, to be founded on the laws of that phenomenon, it still would remain unexplained why this emptying of the paren- chymatous cells does not take place by the most dii^eet path, into the intercellular passages running between them, but into the wood-cells and vessels. The influence which the leaves exert upon the ascent of the sap, 76 ANATOMY AND PHYSIOLOGY OF is connected with the strong evaporation; this not only causes the sap within them to become more concentrated and thus more capable of attracting to itself, through endosmose, the sap con- tained in the cells of the stem (a property which the sap contained iB the leaves acquires the more since its organic, especially gummy, compounds are formed out of inorganic substances), but, as Liebig has shewn, the evaporation from the superficial cells causes the flow of sap towards them by itself, and independently of the en- do&mose they exert. The ascent of the sap through the cells of the stem to the leaves is indeed explicable in this way; but in what way does the activity of the leaves cause fluids in which the open ends of the vessels of a cut stem dip, to be absorbed by the vessels and conveyed upwards in them? That endosmose has no share in this is self-evident, for all the conditions to induce it are wanting. Equally insufficient is the explanation given by L. W. Th. Bi&choff ("De vera vasor. spiral, natur. etfunct/' 62). Accord- ing to his view, the air contained in the vessels is absorbed by the sap of the cells in the different parts of the plant, and used for the chemical transformation of their contents, consequently a fluid which is in contact with the open mouths of vessels must be driven into them by the pressure of the atmosphere. Were this correct, a shoot of which the end was cut off and its vessels there- by opened at their upper extremities, or a tree from which many branches have been cut off, so that the vessels are in communica- tion with the external air in many places, could not absorb fluid into these vessels. But in the ascent of the sap there occurs another phenomenon, which cannot be explained by the endosmose exercised by the cells; namely, the endeavour of the plant to carry up the sap more especially in a perpendicular direction. It is a well-known phenomenon that the bud which stands upon the end of a shoot receives the most sap ; that it grows out into a stronger shoot than those situated lower down; that of two shoots of which one is brought into a vertical position, the other bent sideways or down- wards, the growth of the former is favoured, and that of the other interfered with. The endosmotic force of its cells cannot be altered by this change of position, and yet the strength of the current of sap going to the shoot is altered. All these explanations of the movement of the sap bear reference only to its ascent, not one of them applies at all to the descent of the elaborated nutrient sap. If the bark and the cambium layer attract the nutrient matter from the leaves because their cells contain a more concentrated sap than the cells of the leaves, it is not evident why they cannot draw the sap directly from the root and the wood, instead of by the long circuit through the leaves, and why the bark is wholly incapable of carrying sap up- wards. Gathering all these circumstances together it seems to me to THE VEGET2IBLE CELL. 77 follow from tliem, that the discovery of eadosmose has not solved the problem which lies in the movement of the sap of plants, that in all probability it really does play an important, perhaps the principal, part in the absorption and carrying onward of the sap ; but that as yet we have no definite experiments to enable us to determine accurately the share in the phenomenon which is to be ascribed to this force, and that a series of phenomena exist which are at all events at present inexplicable by endosmose. c. Wutrient Matters. The question, what substances serve for the food of plants, includes a two-fold one : 1, What elementary materials are made use of by the plant in the formation of its substance ? and 2, What are the combinations in which those elementary materials are taken up by plants? The number of elementary substances which occur in plants constantly, and, therefore, must be looked upon as necessary con- stituents, is very inconsiderable, viz.: 1, Oxygen; 2, Carbon; 3, Hydrogen; 4, Nitrogen; 5, Sulphur; 6, Phosphorus; 7, Chlorine; 8, Iodine ; 9, Bromine ; 3 0, Fluorine ; 11, Potassium ; 12, Sodium; 13, Calcium; 14, Magnesium; 15, Aluminium; 16, Silicium ; 17 Iron; 18, Manganese. Observ. These eighteen elements are not all combined in any one plant, for not only can one be substituted for another, which is chemically nearly allied, e, g., potassium for sodium, magnesium for calcium, &c., but al&o particular of them, such as iodine and bromine occur only in certain plants, of which they certainly appear to be necessary constituents. Under these circumstances, these eighteen elementary subbianees are not all of equal importance ; we must evidently lay the greatest weight upon those which occur in all plants, since these are to be regarded as the absolutely ueces&ary constituents. In this respect the firbt fotu' mentioned stand highest, since the principal mass of vegetable substance is composed of them, the first three furnish the material for the formation of cell-mem- brane, and nitrogen is a prmcipal constituent of the proteine substances; sulphur and phosphorus, although contained in inconsiderable quantity in plants, play a most important part, since they in like manner appear to be necessary constituents for the formation of particular proteine compounds. It is different with the radicles of the alkalies and earths, for not only may one basic body be replaced by another m many cases, but even a sub- stitution of ammonia for a fixed base is perhaps often possible. At all events, the latter appears to have been the case in certaia Mould Fungi in wliich Mulder foimd no fixed basic substance; but yet in any case tbis condition must be regarded as a great exception, since alkalies and earths, and indeed particular earths, are necessary to the well-being of all other plants. The universally distributed chlorine is a necessary constituent of certain plants, while iodine and bromiae play in general a very sub- ordinate part. Snicium, iron, and manganese are veiy generally diffused, but in respect to their importance to the life of plants very little is known. 78 ANATOMY AND PHYSIOLOGY OF Tlie questions, whetlier plants iniibt take up from witlioiit the element- ary substances wloicli analysis discovers in them, or wlietlier tliey liave the power of transforming the elements one into another, to live upon pure water, &c., are no longer worth discussion in these days. Whether it be thought probable or not, that the elements of modern chemistry are actu- ally elementary substances^ it has been placed beyond doubt, from Saus- sure's researches onwards through all accurate subsequent observations, that no other substances occur in plants besides those which they take up from without (.ee, especially, Wiegmann and Polstorff " Ueher d, anorgmi, Bestcmdih. d, Fflanzerh'). Of all the elementary substances which enter into plants, oxygen is the only one that is taken up in a pure condition; plants can only appropriate the others out of chemical compounds, which they for the most part decompose. Here at once arises the question, whether the elementary substances when they are to serve as food for plants, must be abeady combined into oiganic compounds, or whether plants possess the power of feeding upon inorganic compounds? On no question of vegetable physiology has so active a strife existed as on this, especially since Liebig (" Ghe-mistry applied to Agricultitre and Physiology ") appeared as a defender of one of the extreme answers to it. No universally valid answer can be given to this question. It is beyond any doubt, that plants, if not as a whole, yet in an overwhelming majority, possess the power of forming organic out of inorganic substances, and that inorganic substances mostly play the principal part in the nutrition. This is evident, both from observations made on a large scale in free nature, and in small artificial experiments. It is a perfectly universal expe- rience, repeated in the same manner in the primaeval forests of the tropics, on the peat bogs, meadows, and heaths of temperate regions, and on the rocky soil of the Alps, that where the vege- tation is left to itself upon a particular soil, and its products are not removed from the ground, masses of decaying organic sub- stances are formed, in consequence of the death of the plants, accu- mulating from year to year, which can of course only be the case through each generation of plants producing a greater quantity of organic substances than it consumes. In a similar way, when an estate is cultivated on proper principles, a certain amount of organic substance is taken away, in the form of grain, cattle, &c., having its origin in the plants grown upon the estate, without the necessity of adding organic matters from elsewhere, and without diminishing the fruitfulness of the soil. The experiments of Saussure also, which are above all to be de- pended on in questions relating to the nutrition of plants, shewed that plants which he grew with water, in a closed space, in an atmosphere rich in carbonic acid, increased their organic substance. He calculated in a manner which does not indeed admit of exact- ness, but still of an approximation to the true condition, that a THE VEGETABLE CELL. 79 plant wMcli stands in a fruitfal garden &oil, cannot owe more than l-20th of its weight to the absorption of organic sub- stances ("Recherches/' 268). An abundance of .experiments which have been made by the greatest variety of observers, have shewn that plants grown in sand which has been heated to red- ness, in metallic oxides, frc, all organic substances being excluded, exhibit growth, stunted though it be, and in many cases form flowers and fruit. It is not requisite to demonstrate more minutely how these circumstances shew the total error of the view, supported, indeed, less by vegetable physiologists than by agriculturists and foresters, that plants subsist solely on the mouldering remains of former plants and animals. But on the other hand, it is not yet proved, 1, that all plants possess the power of living upon inorganic substances, and 2, that the inorganic substances are the sole food of plants ; that the organic substances of humous onlj^ furnish a contribution to the food of plants, in so far as they are separated into inorganic substances by decomposition. This theory which, set up by Ingenhouss, has found its most active supporter of late years in Liebig, must in its one-sidedness be rejected in just the same way as the opposite. In the first place, it is opposed by the no small number of para- sitic plants, which are capable of using for food the sap of living plants, and indeed, in very many cases, only the sap of a particular one, or at all events of very nearly allied plants. A very large portion of the parasites (the Loranthacese) agree with common plants fully in their habit, colour, &c., another portion consist, on the contrary, of leafless plants not of a green colour, which bear the same relation to the plants which feed them, as the flowers and fruit of other plants do to their vegetative oi'gans. In the second place, there exists a very large number of plants, which in part resemble parasites in their exterior and in the want of the green colom^, in part possess the usual aspect, and which derive their nourishment only from vegetable or animal substances in a state of decomposition. To these belong, besides the numerous class of the Fungi, many Orchideas, bog-plants, &c. Thirdly, the majority of other plants exhibit a stunted growth when raised in soil totally deprived of organic substances. In this respect, however, as the experience of agriculturists and foresters has proved, different plants manifest extraordinarily different necessities. While one plant, such as the fir, buck- wheat, Spergula, Sarothamus^ Erica, &c., flourish in a soil which contains only traces of organic substances, others, like the Cereals, require for their vigorous growth, a more or less abundant admix- ture of mouldering substances with the earth. These circumstances indicate that dififerent plants have a dif- ferent behaviour in regard to their nutrition ; that ^ in some the power of living upon inorganic substances prevails, while 80 ANATOMY AND PHYSIOLOGY OF otliers require a mixed food, and, finally, to the parasites are assigned solely the still undecomposed saps elaborated by other plants. Ohserv. From such experime^its made in the rough, of course no accurate bcientific result can be deduced, these can be derived only from experiments carefully made upon a small scale. "We are by no means without experiments on a small scale of this soi^t, but unfortunately most of them have been made in a manner which renders them incapa- ble of furnishing any useful result. To these belong all earlier attempts to grow plants with distilled water, or water containing carbonic acid, in &and, pieces of marble, (fee, in which plants of course would not flourish, but from which no conckision can be drawn, since not merely the organic matters, but all the earths, salts, ko., which they required, were with- drawn from the plants. In order that these experiments sliould furnish any certain result, they woidd require to be made in such a way, that the same species of plant would be grown in a soil wliich contained organic substances, and in artificial mixtures wliich contained all the inorganic constituents of the fertile soil, without the adinixture of any organic constituents. In respect to this, Wiegmann, at my suggestion, made experiments {'' Bot. Zeit,'' 1843, 801), according to which, plants raised in soil devoid of humous grew very poorly and mostly soon died. Mulder made a larger series of analogous experiments (" Fhys. Clmnr\ which like- wise lead to the belief in the use of the organic substances contained in arable soil, as well as of the humic acid and ulmate of ammonia arti- ficially added to it. Even if* these experiments were still far from having decided the ques- tion of the necessity of organic food in a definitive manner, the results are so very concordant with those of experience on a large scale, that there can be no doubt of their general correctness, the more, that these expe- riments made on the smallest scale, obtain a confirmation through the extraordinary small results which manuring with Liebig's solely inorganic manures has everywhere had, when comparative experiments have been made. Instead of reforming agricultui-e by his manures, Liebig has caused them to demonstrate the incorrectness of his theory of the nutri- tion of vegetables. Yet the humous substances in vegetable mould, do not derive their im- portance to plants from an immediate applicability as food, but exercise their great influence on plants principally through their relations with the alkalies and earths, and especially with ammonia. I shall take the liberty of giving some of the principal results of Mulder's researches, since these open out a series of new points of view, which promise to become of the greatest importance to the theory of vegetable nutrition. According to these investigations, the substances beginning to undergo decomposition in the earth are gradually converted into a series of chemical compounds, first into ulmine, then into ulmic acid, humin, humic acid, geic acid, apocrenic, and finally into crenic acid. With the exception of the first and third, these compounds* play the part of acids, and combine in the soil with its alkalies and earths. These acids, con- taining no nitrogen, possess a particularly strong affinity for ammonia, which is always met with, more or less abundantly, in combination vdth them. The compounds of these acids with alkalies are readily poluble THE VEGETABLE CELL. 81 in water, those with earths and metallic oxides little or not at all so. On the other hand, their compounds with the alkalies and ammonia readilj form double salts with the earths aad metallic oxides (apocrenic acid is penta-basic, crenic tetra-basic) ; the alkalies are therefore not only a means of rendering these acids readily soluble, but they assist in conveying the earths into plants by absorption. Alumina plays a special part in reference to crenic and apocrenic acids, since it forms perfectly insoluble compounds with them, in wliich the acids are preserved from decomposition, and cannot be washed away by water, yet they are not thereby completely withheld from plants, since these compounds are capable of decomposition by ammonia, which is thus a means of conveying these compounds into plants very gradually, by continuous decomposition. Most important as the above described relation of the humous acids to ammonia is, since their great affinity for it places them in a condition to attract this body, so important to vegetation, from the air and from tbe animal substances decomposing in the soil, and prepares them for absorption by the roots, yet they acquire still more importance from the fact that, according to Mulder's researches, the continuous decom- position of the humous sul^stances is connected with formation of ammonia, since the oxygen of the air is used for the higher oxidation of the rest of their substance. The evidence that niti^ogen is also con- veyed to plants in tliis way, lies in an experiment of Mulder's (" Fhys. Chemistry''), according to which, young Bean-plants which were raised in an atmosphere free from ammonia, in ulmic acid prepared from sugar free from ammonia, and in wood-coal, with water free from ammonia^ yielded, on analysis, twice or thrice as much nitrogen as the seeds fi*om which they were raised. That the solutions of humous substances in water are absorbed by the roots as ^uch, and not the products of their decomposition, it would cer- tainly be difficult to prove, since these subhtances cannot be demonstrated to exist as such in the plant, but undergo a transformation directly they are absorbed. But in spite of the opposite results obtained by Hartig (Liebig's '^^ Agricidtural Chemistry,'' 1 ed.) and linger {^^ Flora'' 1842, 241), after Saussure's experiments (Liebig ^'-Annal." xlii. 275), Johnson {^^ Mitth. d (Econ, Ge' sells, zu Petersburg," 2 heft 162, extracted in "Wolfi's '^Chem. Forschungen," 202), and Trinchinetti's (^^ JSul facoUa assorhente della radici," 55), the assumption of such absorption is the less unsafe, that it has been long demonstrated, that roots have the power of absorbing dissolved vegetable substances, e.g., tannic acid, narcotic extracts, &c. {See Mulder, " Fhys. Chem.") The inorganic compounds vp-hich are taken up by plants as food, and which furnish them with the four principal elementary bodies which tliey require for their formation, are water, carbonic acid, and ammonia. As the absorption of watery fluids Ixas already been discussed, I now turn to the consideration of carhoniG acid. This, it is well known, exists universally diffused in atmospheric air and in water. Simple experiments prove that plants do not absorb the carbonic acid dissolved in water, with the latter, by means of their roots; 82 AKATOMY AND PHYSIOLOGY OF tat that their green-coloured organs, consequently their leaves in particular, possess in a high degree, so long as they are exposed to lisfht, the facnltv of absorhins^ carbonic acid from the medium, be it air or water, in which they are placed, and of secreting oxygen gas in its place. We owe the more accurate knowledge of this process espe- cially to the admirable experiments of Saussure, which have been fully confirmed by later ones of Grischow, Boussingault, and others. The phenomena may be summed up in the following statements- When green-coloured plants are exposed to the influence of sun- light, under water containing carbonic acid, they exhale oxygen gas. This exhalation of oxygen does not take place in boiled water, "When plants are exposed to the influence of sunlight in atmos- pheric air to which carbonic acid (up to l-12th of its volume) has been added, they remove the carbonic acid and exhale oxygen in its place. This absorption of carbonic acid takes place very soon. Boussingault Q^ JEconomie rurale" i 66) placed a shoot of a Vine bearing twenty leaves in a glass globe, and while the sun shone upon the apparatus, drew through it in an hour fifteen litres of atmospheric air which contained ,0004 to ,0004i5 of carbonic acid, and at the exit of the air firom the globe, the carbonic acid was diminished to ,0001 or ,0002. According to Chevandier's calcu- lations, the trees of a forest, during the five summer months in which they bear leaves, withdraw from the column of air standing above the forest l-9th of its contents of carbonic acid. When a leafy shoot with its lower end dipping in water con- taining carbonic acid, is enclosed in a glass globe, its leaves exhale more oxygen than when its lower end is dipped in common water. A leafy shoot still connected with a tree, enclosed in a glass globe, increases the oxygen gas in the globe. Therefore in both cases the carbonic acid carried up with the ascending sap into the leaves is retained by the latter, and oxygen gas given oif in proportion to it. The exhaled carbonic acid is not contained in the plant in the form of gas, before its separation, for plants which contain no air, like Confervmi or leaves from wliich the air has been exhausted by the air-pump, exhale oxygen in like manner. Pieces of torn leaves possess this function as well as entire leaves; leaves, on the contrary, which have had their organization destroyed by pres- sure, give gS no carbonic acid, neither does the epidermis of the leaf. The quantity of oxygen gas wMch leaves give off depends upon their superficial extent and not on their mass. The secretion of oxygen varies much in abundance under illu- mination by different rays of the solar spectrum. According to the researches of Draper (" Treatise on the forces which produce the organwationof plants/' Appendix, 177), the following amounts THE VEGETABLE CELL. 83 of gas are set free : ia red ; in red and orange 24, 75 ; yellow and green 43, 75 ; green and blue 4, 10 ; blue 1, ; indigo 0. The light here acts according to the intensity of its illuminating power ; the chemical and heating rays of the spectrum are without effect. Ohserv. The amount of oxygen given oJQf is determined by the amount of caii)onic acid furnished to the plant ; the volume of the gas given off from the plant also corresponds to the carbonic acid taken up by it, but the gas exhaled does not consist of oxygen alone, a more or less consi- derable quantity of nitrogen being intermingled with it Draper Q, c. 180) obtained the following results : — > Finns Tmda. Experiment. 1 2 3 Oxygen. 16, 16 27, 16 22,33 Foob annua. Nitrogen. 8. 34 13, 84 21, 67 1 2 90, 77,90 10, 22, 10 When the experiments are made by exposing plants to the sim xinder spring-water, a part of the nitrogen is doubtless derived from the water, as well as another part from the ah' contamed in the air-cavities of the plant; but these circumstances do not explain the exhalation of nitrogen completely, for according to Draper's experiments, it takes place when plants totally deprived of air by the air-pump are experimented on in water containing no nitrogen, and the quantity of nitrogen exhaled in- creases in proportion to the amount of oxygen during the experiment, while the reverse must occur if this intermixture depended on a diffusion taking place between the oxygen exhaled by the plant and the nitrogen contained in the water and in the plant. Draper draws from his experi- ments the conclusion that the exhalation of nitrogen, is a constant pheno- menon, connected necessarily with the exhalation of oxygen, and conjec- tures that it is even the primary pi^ocess which fix^st sets in operation the decomposition of the carbonic acid, that it is to be ascribed to a decompo- sition of a nitrogenous substance in the leaf, which exercises the function of a ferment in the decomposition of the carbonic acid. Boussingault (^^Economie Murahf' i. 5) drew the opposite conchision from the results of Saussure's experiments, since in particular experi- ments the exhalation of nitrogen was so considera«Me, that the nitroge- nous contents of the plant did not suffice for it; he therefore thought we could scarcely assume otherwise than that the nitrogen was derived from the air contained in the water and the plant. Under these circum- stances, a trial of these conditions by accurate experiment is greatly required. The reason that the quantity of oxygen gas given off by the plant is uneqtial to the carbonic acid taken up, is doubtless that a portion of the oxygen gas set free in the green parenchyma of the plant, enters into combiaation with oxidable substances contained in it. Many phenomena a 2 84i ANATOMY AND PHYSIOLOGY OF speak ia favour of tMs. Wlien. cut leaves of water-plants, sucli as YalUs- nerla, Potamogeton, Nymphma, Hydrocharis, &e., lilie tissue of which is traversed by wide air passages, are exposed to light under water, the oxygen does not flow from the surface of the leaves, but from the cut surfaces. It is therefore evident that the gas has to overcome a certain resistance to penetrate the epidermis, and we may fairly conclude that ill many uninjured leaves, a portion of tlie oxygen excreted in the green substances is carried by the intercellular passa-ges and vessels into the Su'^m and roots of the plant, and consequently arrives at parts not green^ which as will appear presently absorb oxygen; consequently a portion of the oxygen must be deficient, on the determination of the amount formed. For this process bpeaks Dutrochet's observation ("ilfe??2oir" i 340), that in Nifmiyh(Ba lutea the air contained in the interior of the plant contains less oxygen the further from the leaves it is taken ; in the roots, eight per cent ; in the stem, sixteen per cent. , in the leaves, eighteen per cent. In accordance with this, stands the fact, that the vessels of the stem of the gourd contain 27*9 to 29 8 per cent, of oxygen by day (Bischoff '^de mra vas spir. naturaj^' 83), while by night no oxygen but much carbonic acid is formed in them (Focke, " de respirat. 'oeget ^' 21). It may be mentioned as a curiosity, that, according to Schultz's state- ments Q^Dle Entdeckung der wahren Pflanzennahmng^^), the whole theory, that plMits exhale oxygen in place of the carbonic acid taken tip, rests upon an error, for the green parts of plants do indeed decompose vegeta- ble acids, and salts of these acids, under the influence of light, but carbonic acid forms an exception to this. Wonderful to relate, hydro-chloric acid; which contains no oxygen, is named among the acids yielding most of it. It is unnecessary to remark that the repetition of the experi- ments by Boussingault, G-risebach, and GrischoWj fully sustain the experi- mental skill of a Saussure against that of the Berlin physiologist. The absorption, of carbonic acid, and exhalation of oxygen by the green parts of plants, nnder the influence of light, are but a part of the complicated relations in which plants stand to atmo- spheric air. In order to form a conception of these, we must at the same time investigate the behaviour of the green parts in darkness, and of organs not of a green colour, Saussure is again the chief guide here. As soon as green-coloured parts are withdrawn from the in- fluence of light, their action upon the surrounding air is converted into the opposite, they now absorb oxygen, and exhale carbonic acid. The amount^ of oxygen taken up varies in the leaves of different plants : within twenty-four hours, from half to eight times the volume of the leaves. The volume of the carbonic acid exhaled, is somewhat smaller than the quantity of oxygen taken up; wlxen the leaves are again brought to the light, they again exhale the oxygen which had disappeared. All parts not coloured green (Fungi, roots, stems, flowers, &c.), whether exposed to light or not, take up oxygen and exhale carbonic acid. It is usual to apply to this absorption and exhalation of parti- THE VEGETABLE CELL. 85 cular kinds of gas, the term respiration. Many Lave regarded the term as inapt, because plants have no organ of respiration, and the like. Let us not contest words, but enquire in what relation these processes stand to each other and to the life of the plant. Plants, from what has been said, have a double respiration, one consuming carbonic acid and exhaling oxygen by day in the green coloured organs, and one connected v/ith a consumption of oxygen and a formation of carbonic acid in the green organs by nighty, and in those not green by day and night. The question, which of these processes predominates, whether, on the whole, the plant consumes or forms a greater quantity of carbonic acid, whether consequently the respiration of plants is on the whole a deoxidating or an oxidating process, is again fully cleared up by Saussure's experiments. When a plant is confined in a definite volume of air, the air is found unaltered in volume and composition after an equal num- ber of days and nights ; thus the plant has formed just as much carbonic acid by night as it has consumed in the day. But if carbonic acid is added to the atmospheric air in which the plant vegetates, or the plant is caused to absorb water containing car- bonic acid, it exhales oxygen into the surrounding air. There can be no doubt that plants in open air are in the same position as those in the last experiment. A very considerable quantity of carbonic acid is continually being added to the atmo- sphere through putrefaction, combustion, the respiration of animals, volcanic eruptions, mineral sources, &c. ; this constant addition of carbonic acid above the usual amount, is again removed from the air by plants and replaced by oxygen. Consequently, plants do not purify the air by increasing the proportion of oxygen in it (if we do not take into account that carbonic acid which is not formed at the expense of oxygen of the air, such as that derived from vol- canic sources), but by the removal of the carbonic acid constantly flowing into the atmosphere, formed at the expense of atmospheric oxygen. In order to become acquainted with the influence which these two kinds of respiration exercise upon the vital operations of plants, we must investigate the phenomena that present them- selves when one or other of these breathing processes is inter- rupted. When plants are prevented, by keeping them from the lights from absorbing carbonic acid and exhaling oxygen, their nutrition suffers and they become etiolated. They do continue to form new shoots at the expense of the nutriment contained in their older parts ; these are even larger than those developed under the in- fluence of light, but weak and soft; the leaves remain small and do not become green, the normal qualities of the saps are not pro- duced, bitter, milky plants remain sweet, &c. Some plants will 86 ANATOMY AND PHYSIOLOGY OE exist for months in tHs sickly condition, but they cannot bear it permanently. On the other hand, when the respiration connected -with the consumption of carbonic acid is stimulated by affording to the plant, while exposed to light, an unusual quantity of carbonic acid, its nutrition is rendered more active. Even when nothing but water and carbonic acid are given, they are able to increase their organic substance, and the weight of this increase amounts to somethinpf like double that of the carbon which is contained in the absorbed carbonic acid. Ohserv. In an experiment of Saussure's, little plants of Vinca appro- priated 217 milligrammes of carbon from the carbonic acid absorbed, and their organic substance was increased about 531 milhgrammes ; two plants oi Mentha sativa consumed 159 milligrammes of carbon and in- creased m weight about 318 milligrammes ('^JKechercheSp^ 226). When the respiration of plants connected with absorption of oxy- gen and formation of carbonic acid, is interrupted by placing the entire plant in air containing no oxygen, for example in nitrogen, or by placing the plants under the air-pump, all their functions at once become paralyzed. The unfolding of the leaves and buds is cheeked and they rot, the leaves no longer turn towards the light ; they no longer exhibit the alternate movements of waking and sleeping; sensitive leaves lose their irritability (Dutrochet, "Me- TnoiTes'' i> 361, 483) ; even single organs cut off fiom air decay while the rest live on : for instance, roots which are covered too deeply with earth. Plants die particularly soon when kept in air devoid of oxygen, in the dark; for example, a Cactus — a plant generally so obstinately retentive of vitality — died in five days (Saussure, I. c. 87). Plants bear being placed in such an atmosphere better when they are exposed to the alternations of day and night, since they exhale a small quantity of oxygen from their own substance by day, and from this form carbonic acid at night, which is again consumed ty day. Plants are capable of holding out in this way a long time, although certainly in a very miserable way and with- out manifesting growth ; but if the small quantity of oxygen which they form is removed by sulphur and ii^on filings, or the carbonic acid by lime water, they are unable to form these gases a second time, and die. It is clear, from the preceding facts, that the respiration of green coloured parts during the action of light is related to the nutrient processes of the plant, since these become abnormal when the function is interrupted, but yet the plant can maintain its existence a long time under these conditions. But that which occurs in common to all parts, and which consists of absorption of oxygen and exhalation of carbonic acid, stands in immediate rela- tion to the life of the plant. If the chemical process, which goes on unceasingly in all the organs of plants, through the action of THE VEGETABLE CELL. 87 oxygen gas upon vegetable substance, be interrupted, tlie plant, just like an animal, becomes asphyxiated, and death, follows quickly. If we wish to speak of a respiration in plants, this oxygen-consuming breathing deserves the name far more than the exhalation of oxygen by the green organs, connected with the nutrient processes. In this immediate relation to life the respira- tion of plants corresponds completely with the respiration of ani- mals ; oxygen gas is a true vital air to plants. But the behaviour of the plant towards the atmosphere becomes the more compli- cated, that it does not merely absorb oxygen from without, like the animal, but also a part of that prepared in its own green organs. Obser^. Liebig must shut Ms eyes to facts lying open before Mm, wlien lie persists {^^Agricultural Chemistry,'' 6th ed.) that the respu'aiioa consum- ing oxygen does not exist, that the absorption of oxygen has notMng to do with the life of plants, but is a process of oxidation, which occurs in dead wood as in the hvmg plant, and that the exhalation of caibonic acid stands m no connexion with the absorption of oxygen, but that the car- bonic acid simply rises in the stem with the water taken up by the roots, as m a cotton wick, and so passes out into the air. Although the great diffusion of water and carbonic acid almost everywhere give full opportunity to plants, of appropiiating the three principal elements of their substance (carbon, hydrogen, and oxygen), they have not always the opportunity of absorbing the quantity of nitrogen requisite for a vigorous development, whence the important part which nitrogenous substances play in manur- ing. The nitrogen of the air is a perfectly indifferent body to- wards plants. Even Saussure indicated that plants can only take up nitrogen in the form of solutions of organic substances or of ammonia ; the latter has been especially maintained by Liebig, and his was the merit of demonstrating by experiment that ammo- niacal vapours exist in atmospheric air, and that ammonia occurs in all rain and snow water ; and on the other hand, of directing attention to the presence of abundance of ammoniacal salts in the ascending sap of the Maple, Birch, &;c. "Whether, however, as Liebig assumes, the ammonia contained in atmospheric air suffices to furnish the nitrogen contained in wild plants, and that^an abundant supply of ammonia from the soil is necessary to culti- vated plants, only because it is desired to stimulate them to the production of a great mass of the constituents of blood, is quite a different question. In the first place, no experiment has shewn that plants are capable of applying to their nutrition the ammo- niacal vapours contained in the atmosphere ; secondly, it is even doubtful whether this is the case with the ammoniacal salts which they take up by their roots, for, according to Bouchardat Q' Re- cherches sur la Vegetation,'' 24), these salts, when absorbed by plants in watery solutions are poisonous to them in a state of 1000 or 1500 fold dilution. But it is proved by abundant expe- 88 ANATOMY AND PHYSIOLOGY OF rience that ammoniacal salts mixed witli the soil, greatly further the growth of plants. These diffeient results render it in the highest degree probable tliat tlie ammoniacal salts enter into com- binations ^-vith the constituents of the soil, which exercibe a dif- ferent action upon the plants, from that of the pure salts. In this respect the investigations of Mulder upon the humous substances are of the highest value. Accoiding to these, carbonate of ammonia cannot exist for any time as such in humous, but is decomposed by the organic acids of the soil; since therefore compoiinds of ammonia with sulphuric and hydrochloric acids, fee, must be converted by the carbonate of lime in the soil into carbonate of ammonia, there exists the highest probability^', that plants always receive ammonia in combination with the organic acids of the soil, which would explain the difference between the poisonous action of pure ammo- niacal salts and their favourable influence when mingled with the soil. Moreover, it is not by any means proved that the air con- tains enough ammonia for us to regard it as anything like a suffi- cient source of nitrogen to plants, while Muldei's experiments point to a production of it in the soil ; in any case the amount contained in the soil is very considerable, according to Kidcker (Bei'zelius, " JaliresheTicht," xxvi. 265) it amounts to 4045 pounds in a layer ten inches deep extending over a hectare in sandy soil, 2 OS 1 4 in argillaceous soil. From these ciicumstances as well as from the expermients of Boussingault and Mulder, it in any case follows, that the roots and not the leaves take up the substances which furnish plants with nitrogen, while, on the con- trary, the leaves play the especially active part in the absorption of carbonic acid. d. Elaboration of the Nutriment, "We know scarcely anything of the chemical processes in the interior of plants, on which depend the assimilation of the nutrient matter taken up, and the gradual conversion of this into the various compounds which the plant contains. In considering the nutritive processes of plants, two circumstances first strike us. 1, The uncommonly great agreement of all plants in lespect to the prifduction of a series of neutral hydrates of carbon, which furnish the material for the solid parts of plants, as also in respect to the formation of proteine-substanees which play an active part in the process of development of the cell ; 2, ^n infinite variety of chemi- cal compounds, which are deposited in the different organs of particular groups of plants, in spite of the uniform structure and the agreement in the nutrient process, so far as relates to growth. The chemists of our days, especially Mulder, have sought to make comprehensible the formation of such a surprising abundance of products by bodies so simply and uniformly organized as plants THE VEGETABLE CELL. 89 are. Since the plant is a complex of closed vesicles filled with fluid, the contents of which stand in reciprocal connexion by en- dobmose, this structure alone affords the possibilitj^- of tlie forma- tion of the most varied chemical coiiipouiids. Even if we would suppose a plant to contain a fluid of the same composition in all its cells, this equilibrium could not last a moment ; for on the one side the sap in the cells of one organ would acquire more con- sistence through evaporation, and tlicrchy call into existence an opposition toward the otlier cells, while in the cells of anotlier organ endosmose might cause the absorption of a thinner fluid, and thus give lise to a flowing of tlie sap from this organ to the former, — wliich would at once cause a nuiltiforjuity of the compo- sition spreading bhioughout all tlie organs. Wbcn we take into consideration, that on one side ammonia with organic compounds are taken up by the cells, while on the otLer side carbonic acid is decomposed, its caibon appropriated, and its oxygen given out, moreover that the cell-walls act by contact upon the contents of the cells, and that this action again differs according to the differ- ent chemical qualities of the cell-wall and contents, — ^it becomes explicable how the most manifold transformations of cell-contents and the formation of abundance of pi o ducts come to pass in the Vegetable Kingdom, the only limitation that exists being the fact that the elementary substances do not combine together under all conditions. This is all correct enough, but it does not advance us one step in the knowledge of the processes of vegetable ixutrition. When we place the contents of all the vessels in a chemical laboratory in a condition of reciprocal connexion, we certainly expect that an innumerable series of chemical processes will result, but what they will be we know not, unless we know what the contents of each vessel consist of, and in what order and under wliat circum- stances the contents of one come into operation upon the contents of another. It is of this that we are ignorant in plants, and so long as it remains uninvestigated, we can only set up more or less probable conjectures. These circumstances will be my apology for treating this sub- ject as briefly as possible. One of the most general phenomena, since it occurs in all green-coloured plants, is, as we have seen, the absorption of car- bonic acid, and the exhalation of oxygen gas. The experimen'ts of Saussure demonstrate that this process stands in most inti- mate connexion with the formation of organic substances; no- thing seemed easier than to explain this process. The neutral compounds of the plant (sugar, gum, starch, inuline and cellulose) are composed of carbon and the elements of water; it was only requisite to assume that the carbonic acid was decomposed in the leaves, its oxygen given out as gas, its carbon combined with water, which is never wanthig in the plant, and the entire pro- 90 ANATOMY AND PHYSIOLOGY OF cess was elucidated in the simplest way. This theory conse- qiiently met with "universal acceptation, and in all books the decomposition of carbonic acid, taking place in the leaves, is spoken of as a settled fact, but we are without one proof that such is actually the state of the case. Liebig remarked, that it was far more probable that it was not the difficultly deconiposable carbonic acid, but the readily decomposable water which was separated into its elements, and its oxygen given off, while its hydrogen entered into combination with the carbonic acid. The result was of course the same. There is no means of testmg the correctness of either of these theories. But it is possible that they are equally false, that the carbonic acid does not enter into combination with the hydrogen of the water, but with another substance contained in the plant, and that oxygen becomes free by the decomposition of an organic substance previously formed. The latter is the opinion of Mulder, who assumes that the plant does not decompose carbonic acid because it is green, but while it is becoming green; new chlorophyll is constantly forming under the injluence of light, with this originate the wax and starch associated with it, and an excretion of oxygen is necessarily con- nected with this ; and this oxygen goes off partly in the form of gas, and in part oxidizes the colourless chlorophyll, and converts it into green. On the other hand, Draper, on account of the ex- halation of nitrogen which he regards as necessary, assumes that chlorophyll acts the part of a ferment in the process of decompo- sition of carbonic acid, and in this itself suffers a decomposition, in consequence of which nitrogen is set free. Thus, at the very first step of the nutrition of vegetables, which was supposed to be the most thoroughly investigated, opinions become divergent; each has a certain probability, not one is proved. The only cer- tainty is, that carbon and water remain within the plant, and are applied to the formatiou of its organized, substance. ^ On the question of the combinations into which the absorbed nutriment first enters, the views of chemists stand in no better agreement. Saussure's experiments shewed that plants to which cai^bonic acid and water were afforded, acquired increase of weight equal to about twice the weight of carbon taken up. It may be considered probable, as Davy assumed, that the car- bon absorbed enters at once into a neutral combination with the elements of water; in all probability this compound is soluble in water; since, therefore, dextrine is found in all green coloured organ>s, it is not unlikely that this, or in other cases, sugar is the form under which the said inorganic substances combine into organic substance. But another probability is opposed to this notion, that the con- stituents of water and carbon enter at once into a neutral com- bination. All plants contain, besides the neutral substances, organic acids, in which the oxygen bears a greater proportion to THE VEGETABLE CELL. 91 the hydrogen than in water. Among these acids, oxalic is one of the most widely diffused, — scarcely a plant being without it. This acid stands very close to carbonic acid, since — supposing it anhydrous — it contains no hydrogen, and differs only from car- bonic acid, by containing less oxygen. It may, with Liebig {^'Agricult. Ghem ,"' 6th ed.), be considered very probable, that the deoxidizing process connected with the respii^ation of the green organs, does not convert the carbonic acid and water at once into neutral compounds, but first only a partial separation of oxygen takes place, and the carbonic acid is changed into organic acids, fi.rst of all into oxalic, the hydrate of which, by separation of greater amounts of oxygen gas, can be transformed into malic, citric, and other acids. It may be assumed of all these acids that they are capable of conversion iuto sugar, starch, &e., by the addition of hydrogen. If this conception is adopted, the con- stant occurrence of vegetable acids appears a necessity for the nutritive processes of plants ; and it will explain why plants will not flourish when they do not take up a certain quantity of basic substances, to combine into salts with these acicls. On the con- version of an acid into a neutral substance, the base becomes free again, can unite with a new portion of acid, and so in the course of time, a comparatively small quantity of base may bring about the formation of a very great quantity of neutral compounds. Observ. This notion of the importance of acids in the vegetable eco- nomy, has something very attractive about it, since it appears to solve a series of questions, but on closer examination a number of doubts present themselves. On the one side, the assumption that the acids are foimed by a decomposition of carbonic aeid, appears in any case too general, since in many plants with fleshy leaves, an acid is formed every night (thus at a time when no carbonic acid is decomposed), which acid is again decomposed by day. Here the acid is doubtless formed through oxida- tion of a neutral compound. On the other hand, that theory does not perfectly explam the case of the basic substances. If these had no other destination in the plant than the purpose of fixing free acids, it would be all one to plants whatever base was absorbed from withotit ; any one could be substituted for any other. This is certamly, in some degree, the case with regard to bases which are very closely chemically allied, like potash and soda, or lime and magnesia, but this substitution is only coiBpatible to a certain extent with the healthy growth of the plant. Particular plants require particular bases, lime, potash, &c., and die when they do not find them in the soil. Therefore, the specific properties of the bases stand in a definite relation to the nutritive processes of plants, albeit, the grounds of this relation are still unexplained. If, moreover, the acids form these transitional stages between carbonic acid and the neutral compounds, it is remarkable that so many plants produce an acid, and especially carbonic acid, in far greater quantity than is neces- sary for this purpose, depositing it, ia combination with lime, in an in- soluble condition, crystallized in the celK, and yet do not subsequently 92 AK ATOMY AND PHYSIOLOGY OF re-dissolye these crystals. It is true tliat nutritive substances (starch, fixed oils, &c.) are frequently produced in greater abundance than the i^equirements of the moment demand, and are deposited in the cells of particular organs, but these deposits are only temporary accumulations of food to be made use of subsequeiitly; those deposits of insoluble salts appear much more likely to be intended to remove from the circuit of active juices, compoundb which are superfluous to the plant. Again, this theory does not explain the exchange of different bases at different periods of the age of the same organ. From the analyses of Saussure was deiived the general rule, that young organs are espe- cially rich in soluble alkaline salts, older plants in earthy salts and metals. A second doctrine propoimded by Liebig, is connected most closely with this opinion as to the office of the alkalies to neutralize the organic acids, namely, the notion that for every species of plant, the amount of oxygen of the carbonic acid contained in its ash, in the combustion of salts originating from vegetable acids, is constant, xio matter what soil the plant may grow upon (^^AgricuU, Chem,'' Qth ed ). For Liebig assumes that a plant forms no more of the acids which it produces, than is directly requisite for its vital operations, and that these thei'efore take just so much alkali as will fix these determinate quantities of acid. But weighty objection's may be opposed to this doctrine. I have already ob- served that many plant*^ do not produce the organic acids in that quan- tity which they would require were these converted into neutral com- pounds, but in very coubiderable &U2)erabundance, as for example, all specimens of Gaotus unceasingly deposit extraordinarily large masses of tartrate or oxalate of lime in their cells, as insoluble crystals; the oxalic acid of these crystals is wholly withdrawn from the nutrient operations, yet elementary analysis would make its lime appear to exist in the state of carbonate, while at the same time, no conclusion could be drawn from its quantity, as to the amount of acid neces'^ary in the nutrient processes of these plants. Moreover, all the alkalies which appear in the ash as carbonic salts, are not combined with organic acid in the living plant, but in many plants crystals of carbonate of lime occur ; carbonic salts are deposited in the sxibstance of many cell-membranes, and all cell-mem~ branes are combined with alkalies and eaiiihs ; consequently, we cannot draw from the analysis of ashes, as Liebig assumed, a proof of that law, and this is the less possible since, moreover, the fixed alkalies may be replaced by ammonia. Whatever may be the character of the chemical action to which neutral compounds ovt^e their origin, it is at all events, beyond doubt that they are produced by a deoxidizing process taking place under the influence of light. The effect of the deoxidation extends still further, for there can scarcely be a plant which does not contain compounds in which the oxygen is not contained in smaller quantity, in proportion to hydrogen, than in water, even if it be not altogether wanting. To this class belong chlorophyll and the wax connected with it, the incrusting substances of the wood-cells, the fixed and essential oils, resin^ caoutchouc, &:c. "With the exception of the fixed oils, wMch doubtless originate THE VEGETABLE CEIL. 93 from starch, we are ignorant from what other compounds all these constituents are derived ; yet there can be no question that theii' hydrogen is originally obtained from "water, and tliat their origin is connected with a separation of oxj^gen. It is remark- able of many of them, especially in the formation of essential oils, how much their production is favoured by the action of strong sunlight. The compounds containing nitrogen stand in opposition to those devoid of it. Though in quantity they may stand far behind the latter, their importance in the vital phenomena of plants is not less ; nitrogenous substances, as we have seen, line the cell as the prhnordial utricle, and consequently the contents of the cells are ordered under their immediate influence ; they originate the de- velopment of new cells, and set in action the decomposition of carbonic acid. Doubtless these constitute but a few fragments of the great part wliich these substances play in the Living plant ; for many chemical processes, such as fermentation, the formation of hydrocyanic acid and amygdalin, the conversion of starch through diastase, &c., indicate that the iirst impulse to the transformation of all vegetable compounds, is principally given by the proteine substances. The great importance whicli these substa^nces have in the vital economy of plants, is also denoted by their anatomical conditions, since they are contained in great abundance in all organs destined to farther development, and which are endowed with more important physiological activity ; e. hoThha^ mucilaginous from the Legwminosw, &c. At the same time, he be- lieved that he found acetate of lead taken up by the plant, again excreted in this way, further, that in water whereinto these secro- u 98 ANATOMY AND PHYSIOLOGY OF tions liad passed, plants of the same species would not flourish, while other species conld absorb it with impunity. From these experiments, De Oandolle drew the conclusion that these excre- tions were to be compared with the urinary excretions of ani- mals, and explained from the doctrine, that no organized being could use its own excrement for food, the fact of experience, that cultivated plants, the Cerealia for example, would not flouiish for any long uninterrupted period upon the same soil. The repetition of these experiments by others, left no doubt that Macaire had not gone to work with the requisite circumspec- tion in making them, Braconnot (" Ann, d. Chimie. et d Physf' torn. Ixxii.p. 32) shewed that milk-sap was effused into water from the roots of plants of Lactwoa which had been dug out of earth, partly in consequence of laceration, partly in consequence of irritation; buit that earth wherein Neriiim, JEtq^horhia^ Asclepias, and Papaver^ had grown, some of them for a series of years, was totally devoid of such excreted matters, and that merely traces of organic substances, neither bitter nor acrid, were met with in it, and these he attributed to the decomposition of the rootlets. The experiments of Walser ("Unters, UK d, WuT^elausscheiduti- gen" Dissert. Tubingen, 18S8) likewise gave a completely negative result, as did also Boussingault's (^^Ann. d. Ohim. et d. Physf' 1841, torn, i,, 217). Moreover that the noxious salts absorbed are not excreted by uninjured roots, but only extracted by the water from injured roots, was shewn by the experiments of linger ( " Ueb. d. Vegetat v. KitzbuheV 149), and Meyen (^^Pliysiologf' ii. 530), on Lemnaj and Braconnot demonstrated that Macaire had made a clumsy mistake in his expeiiments, to prove the excretion of an absorbed salt of lead, since he overlooked that the close bundles of roots carried the solution of the lead salt over, into the vessel of water into which another portion of the roots of the same plant dipped, by capillary attraction. Under these circumstances, we must regard the secretion of an excrementitious fluid by the roots as not proven. At the same timej it is certainly no evidence that the roots do not excrete at all. I lay no weight upon the reason mentioned by Schleiden, that the endosmose of the roots must be accompanied by an exosmose, for it is too hazardous to deduce the existence of a second phenomenon from one of which so little is known in regard to the forces active in it, as is the case of the absorption of the roots. A few other circumstances perhaps speak in favour of it. Many experiments shew that the roots of living plants exert a chemical influence upon organic substances placed in contact with their roots. Trinchinetti (^^svM.fac, absorh d. radioi." 57) observed, that a decoction of humus underwent foetid putrefaction when left to itself, but this did not take place when the roots of living plants were placed in it. In many cases it is observed that the roots exercise a solvent action upon solid organic substances; thus THE VEGETABLE CELL 99 Ga^^zeri saw this in Clover ; Trincliinetti saw a root of Xepefa CuMria grow throiigli tlie midst of a peacli-stone, and the roots of VisGum penetrate into the periderm and bark of a tree. There can be no donbt, that these effects are produced by a sub- stance excreted from the roots. Of what kind this is, we know not; yetBecquerel (Guillemin, ^^Archiv. deBotanique,'' 1 398) has given an indication in this direction, since he found that roots ex- creted a free acid (probably acetic acid), or a substance which was converted into an acid in air. This circumstance reminds us that Lichens which live upon limestone dissolve the latter, and form their fruit in excavations of it, which can only be through secre- tion of a free acid. Whether the above-mentioned effects are to be ascribed to the free acid excreted by roots, or to the secretion of other compounds is not made out. According to BecquereFs researches, this excretion of a free acid occurs not only from the roots, but from the other parts of plants — ^the bulbs, tubers, buds, and leaves. Becquerel brings it into connection with the evapo- ration of acetic acid in human perspiration ; if this analogy were recognized and the secretion thus interpreted as a true excretion, there would still be no inconsistency in imagining it to exercise a function, contributing towards the accomphshment of the pur- poses of the living plant, even in its excreted condition. Ohserv. Moldenbawer (" JBeitrage z. Anatomic d, Pflanzen^' 320) ex- pressed the opinioiL that the organic stibstances used by plants for their nutrition, underwent a chemical decompositioii by a iiuid secreted from the roots, and wei'e thus prepared for assimilation. This theory has been revived, in recent tunes, by Schultz (" I)iQ Entdeckung d&r ivahren PJfanzennaJiTuyig''). He believes that he found living plauts (roots a"=t well as leaves) decompose solutions of the most varied organic substances with evolution of oxygen, before they absorbed them; thus humous- extract becomes acid, milk-sap decomposed, and cane-sugar converted into starch-gum. From this he concluded that plants act on the assimi- lated compounds m. a manner analogous to that of the uxtcstinal canal of animals upon their food. How much of truth or error there exists on this matter must be decided by future researches of chemists. "While some discover a removal of excrements in the secretion of a watery fluid by the roots, others ascribe the same purpose to an aqueous secretion through the leaves. Isolated observations had long ago indicated that water is excreted, during the night and morning, in the form of drops of liquid, if not from all, yet from a great many leaves, since the drops of water which are formed at the points and serrations of leaves, owe their origin to a secretion, and not to the dew. This subject was especially fol- lowed out by Trinchinetti (" On a hitherto imdescribed fit notion of the Plant" — Literal hlait ^urLinncea, xi 66) ; he found little glands (which he called glaiodulm periphyllce) at the spots where the excretion took place ; the fluid secreted from these, though it H 2 100 ANATOMY AND PHYSIOLOGY OF appeared at firbt like pare water, contained organic sub&tances, and passed into foetid decomposition. Similai observations were made by Eainer Graf (" Flora;' 1840, 433), ^ Wliile this excretion of water occurs only in very small amount in most plants, manj;^ of the family of the Aroide^e, especially Galla mthiopica (Gartner, ^^Beihlatter zut Flora" 1842, 1), Arura Colo- c isia (Schmidt, in Limicea, vi. 65), evacuate water in larger quan- tity from the points of their leaves, so that it flows off in diops ; this occurs in the most striking degree in a plant described as CaladiuTTi destillatorum (" Aom, of Nat Hist" sec, ser. i. 188), in which each leaf — it is fcrue, of colossal size — gave off about half a pint every night. The water flows here (as in Arum Golocasid) from an orifice in the neighbouihood of the point of the leaf, upon the upper surface, in which terminates a canal running along the border of the leaf, while smaller canals, running along the prin- cipal nerves, open into this. The water secreted, in all these cases, contains but an extremely small quantity of organic substance in solution. It is probable that the secretion of water in the pitchers of Nepenthes, Sarracenia, and Gephalotus, should be reckoned with the above. According to Volcker s account (" Ann. of Nat Hist" sec. ser, iv. 1 28), the fluid secreted by Nepenthes contains only 0,27 — 0,92 per cent, of solid matter, consisting of citric and malic acids, chlorine, potash, soda, lime, and magnesia. We have no data which would enable us to determine accu- rately how far this secretion of drops of fluid water is (as accord- ing to Trinchinetti) for the purpose of evacuating substances, which, if they remained in the plant, would exercibe an injurious influence upon its health; yet this hypothesis hardly appears probable, when we take into account the extraordinarily small quantity of organic compounds removed in this way, together with the circumstance that they bear none of the characters of a substance beginning to sufler decomposition. The same holds good, also, in regard to the water excreted from the leaves in the form of vapour. This likewise contains, as the observations of Senebier and Treviranus shewed, an ex- tremely small quantity of organic matter, but is nevertheless capable of putrefaction. Experiments which were m ade by Bonnet, Duhamel, and Treviranus {'' Phys!' i. 494), to hinder the evapora- tion, by smearing the leaves with oil and other substances, shewed that the leaves died. This result may, however, be just as well attributed to a positive injurious effect of the oil, in withholding PIT, as to a suppression of the evacuation of injurious matter. Manifold experience puts it beyond doubt that repression of the evaporation from the leaves by unfavourable conditions of weather, produces disease, often connected with the formation of Fungi, but this result may be caused quite as much by a disturbance of the normal nutrient processes of the plant connected with the evapora- THE VEGETABLE CELL. JOl tion of a Large amount of aqueous vapour, as by the retention of an organic substance which should have been excreted by the leaves. f. E'volution of heat With the nutritive processes of plants is connected their power of producing heat. That plants possess this power may be de- monstrated by simple observations, but these require great ac- curacy and certain rules of precaution, to avoid arriving at false conclusions ; for in determining the proper heat of plants, not only does the mostly very small amount of heat which is capable of raising the temperature of the plant a little above that of the air, render great caution necessary in making the experiments, but, under common circumstances, so much heat becomes latent, through the active excretion of aqueous vapours from the leaves, that the temperature of the plant, in spite of the latter producing heat, sinks below the temperature of the surrounding air. Theie- fore to arrive at accurate results, it is not merely necessary to use a very sensitive thermometric apparatus, but also to cut off the refrigeration by evaporation. That seeds when germinating, as they lie heaped in large masses, evolve a considerable degree of heat, is a fact long known from the malting of grain, but the cause of it was incorrectly sought for in a process of fermentation. To Goppert f'" Ueher Warmeen- hvickelung in der lehenden Pflanze") is due the merit of having demonstrated that such is not the ease, but that the evolution of heat is connected with the process of germination. Seeds of very different chemical composition (of different grains, of Hemp, Clover, Spergula, Bmssica, &c) made to germinate in quantities of about a pound, became heated, at a temperature of the air of ^S°— 66°, to 59—120° Fahr. It was likewise shewn by Goppert, that full-grown plants, also, such as Oats, Maize, Gyperus esculentus, Hyoscyamus, Sedum acre, &c., laid together in hcaps^ and covered with bad conductors of heat, cause a thermometer placed among them to lise about 2° — 7^" (Spergula ate much as 22°) above the temperature of the air. Dutrochet succeeded, with the help of BecquereFs thermo- electiic needle, in demonstrating an evolution of heat in plants standing alone (" Ann. d. sc, not" 1 8S9, ii. 77) ; but here the cold of evaporation must be cut off by placing the plant in an atmosphere completely saturated with water. Under these circumstances, the temperature of all vegetating parts, the roots, the leaves, the young juicy shoots (but not those of hard wood), were elevated from about one l-6th to 1-1 2th of a degree. The evolution of heat exhibited a daily maximum and minimum ; the latter oc- curred about midnight, the former about noon, yet not at the same hour in different plants, for the time varied from 10 AM.. to 2 P.M. 102 ANATOMY AND PHYSIOLOGY OF Ohserv. Tlie earlier expcrinients to determine tlie temperature of plants, by sinking tliermometers in holes bored in tbe triinkb of trees, were completely incapable of giving a decidre answer to the question whether plants evolve a proper heat, since a number of ciicumstances, the effect of which cannot be taken into account, are influential upon the temperature of the tree, namely, the direct warming action of the rays of the sun, the cooling influence of evaporation, the sometimes warm- ing, sometimes cooling communication of the temperature of the soil, through the medium of the ascending sap, which exercises an influence according to the time of year, and the difference of depth to which the roots penetrate, not to be accurately determined in isolated cases. Under these circumstances, it is readily explicable that the experiments made by different observers do not agree. While I^au found that the mean tem- perature of the tree agreed with the mean temperature of the air, Schubler found the tree 1^" to 2f ° colder than the air in summer, and in spring, on the contrary (March, May), about ll** to 3° warmer. While in the experiments of Schubler, made on pretty thick trees, the temperature of the latter never attained the extreme of the temperature of the atmosphere, Beaumur saw slender trees heated 18° to 29° above the temperature of the aii', in the sun. Under these- circumstances, the slight evolution of heat of single plants must vanish without leaving a trace, in. the considerable, and, in some cases, discordant variations of temperature, dependent on external influences. A very great evolution of heat occurs in the blossom of the Aroidese. This is considerable even in our Arum maculafum, and, according to Dutroehet^s researches (" Go')nptes rendus" 1839, 69 o), rises to 25" — 27° above the temperatnre of the air. But this phenomenon is seen 7"^ far higher degree in Golocasia odora, in wliicli plant it has been investigated by Brongniart (" Nouv, Ann. d. Museum," in.), Vrolik and Vriese (" Ann, des Sc. Nat!' sec, ser, V. 134), and Van Beet and Bersgma ("Obs, ihermo-eleet s. Velev. de teonpcrat dee fleurs d, Oolocas. odor" 1 838). These last ob- servers found the maximum of heat 129*", -when the temperature of the air was 79°. The seat of the strongest evolution of heat alters during the time of flowering ; namely, after the spathe has opened, the antheis manifest the greatest heat ; they begin to cool down with the emission of the pollen, after which the upper part of the spadix, covered with abortive stamens, grows warm. Similar observations — ^not, however, made with the thermo- meter, and therefore not fitted to give an accurate determination of the heat given off by flowers — ^liave been made on Arum italicum, A. Dracunculus, Galadmm viviparum, G pinnati- fidum, and Galla cethiopica, by Sausa^ire, Goppert, Schultz, Tre- viranus, Gartner, and others. The evolution of heat in the blossom of the Aroidese exhibits a daily maximum and minimum, which, howevei^, it is remarkable, that different observers found to occur at different times of the day ; thus, in A, ^niaculatum, the maximum occurred in the morning (Dutrochet), wliilst Senebier found it occur after six THE VEGETABLE (JELL. 103 o'clock ia the evening ; in Golocasia odora, Brongniart found the maximum at 5 A.M ; Vrolik and Vriese, as well as Van Beek and Borgsnia, about S P.M. ; and Hasskoii, in Java, at 6 A.M. (" Tldschr. V. naturl. Gesch." vii letterkund Berir/t 26) ; as also Hubert found, probably in the same plant, the greatest heat after sunrise, in Madagascar. In very few cases has evolution of heat been observed in the blossoms of other families. Saussure, by means of an air-thermo- meter, found tlie flowers of Gourds V to 3°, those of Bignonia radioans V, of Polijanthes tuberosa J-°, and Mulder those of Cactus grandifioTiis i° — 2° Fahr. warmer than the atmosphere. There can be no doubt that the evolution of heat frorti flowers results from the respiratory process connected with the formation of a large quantity of carbonic acid. Saussm^e found that a blossom of Arum ^inacidatuon consumed in. twenty-four hours, before its heating, or after it had ceased, five times its own volume of oxygen, while a warmer blossom consumed thirty times, its spathe five times, the bare portion of its spadix thirty times, and the part covered with flowers 132 times its volume of oxygen. Yrolik and Vriese (" Ann, d. Se, Nat sec. aer" xi. 62) found the heat of a blossom of Golocasia odora increase about 9° to lO"", when brought into oxygen gas, while no evolution of heat took place at all in carbonic acid. In like manner, there can be no doubt that in germinating seed, the respiration of which is equally connected with the con- sumption of oxygen and the exhalation of carbonic acid, the evo- lution of heat stands in connection with the formation of carbonic acid ; but whether this source furnishes all the liberated heat, or a part of it depends upon the vegetative process of the germina- ting seed, cannot be determined in the present imperfect state of our knowledge of the chemical transformations of the substance of the seed connected with germination. In vegetating organs the source of heat is evidently different. It is true, as we have seen, that oxygen is consumed and carbonic acid formed by all organs, but since on the whole a greater quan- tity of carbonic acid is decomposed in the green- coloured organs, than is formed in the remaining parts, more heat must be consumed than produced in the respirating process of vegetating organs. But evolution of heat must be connected with the nutxient process, for the plant forms its organic substance, if not wholly yet in great part, from gases and liquids. Since then the growth of the plant exhibits a daily exaltation, occurring about noon, it is quite m accordance that the evolution of heat also should occur in in- creased degree at the same time. \0h ANATOMY AND PHYSIOLOGY Of B.-THE CELL AS AK ORGAIST OF PROPAGATIOISr. a. The Multiplication of Plants hy Division, Multiplication by division occnrs nnder different forms according to the lower or higher stage of organization of the plants ; for the lower it is, the more does the individual cell possess the power of independently producing a new vegetable, whether by simple division or by the formation of a bud ; while the higher the or- ganization of the entire plant stands, the more does the capabihty of maintaining an independent vitality leave the individual cells and become committed to smaller or larger assemblages of cells, which must become developed into an organ of complicated structure, before their separation from the parent plant, to ensure their growing up into independent plants Multiplication of plants by division of every individual cell is a very common phenomenon in the lowest forms of Algse. In the geneiality of cases, the dividing cell parts into two, more rarely into four cells, in which again the same process of multiplication may be repeated. This is of universal occurrence in the uni- cellular Algae, e, g., in the Diatomaceae, DesmidiacesB, &c. ; after the division, the newly-formed cells either separate from each other or remain joined together in colonies arranged in rows or flat layers, more or less firmly connected by a mass of mucilagi- nous matter, thus forming a transition towards the plants com- posed of numbers of cells. The same process is repeated in the many-celled Algae, for example, in the Oscillatorieae ; in the first instance, growth of the single individual is the result of the process of division of the cells in these plants, but the extraordinary readiness with which they break up into separate pieces, or, as in Nostoo, the single cellular filaments separate fi^om each other by solution of the connecting mucilage, together with the power of the single pieces to grow up again into new plants, give great facihty to the mul- tiph cation of the individuals by division of their cells. The capability of multiplying in tliis way by unceasing divi- sion of the cells, appears to be unlimited in many lower plants, such as the Diatomacese, Oscillatorieae, &c ; at all events, any other mxode of propagation has been either rarely or not at all discovered in them; in other cases, however, and especially in the Desmidiacca? {see Ealfe' ''British Desmicliem,'' 5) this division is confined within definite limits. After a series of divisions have taken place, this process ceases, and the formation of spores begins. Among the plants possessing a thallus composed of numerous cells, the development of single cells or groups of cells into inde- pendent plants occurs chiefly in the Lichens, where very frequently the layer composed of globular cells breaks up, by the cells fall- ing apart into the form of powder (gonidia, lagerkeime), either THE VEGETABLE CELL. 105 at particular points or all over the tliallus, these cells falling upon foreign bodies and becoming developed into new plants, if they find a favourable station. But this phenomenon is to be regarded a*s more or less a result of disease, for the normal development of the thallus is interfered with by it, and if the formation of goni- dia occm-s to a great extent, is perfectly arrested ; thus this mode of multiplication of Lichens becomes the more inconsiderable in proportion to that by spore^s, the more favourable the station to the normal development of the plant, and vice versa. The same phenomenon is met with again in the leaves of the Jungerman- niese, which frequently break up more or less completely into pulverulent masses of isolated cells ; but it has not yet been ob- served whether these are capable of further development into new plants. But the formation of the so-called gemonce occurs nor- mally in many frondeseent Liverworts, especially in Lunularia, Marchantia, and Blasia. These structures are developed, in hollow receptacles of various form, from a stalked cell, which is converted by repeated subdivision into a cellular nodule, which becomes detached, readily strikes root, and grows up into a new plant. (See Mirbel, ^^ Recherck 8. I. Marohantia polymorpha.") Far more important, or perhaps merely better known, through the masterly researches of W. P. Schimper (" Bech, AnatoTn. et MoTph. s. L Mousses'')^ than in the Liverworts, is the part played by multiplication through independent gTOwth of single cells in the Mosses, for almost every cell of the surface of these plants is capable of conversion by repeated division into a cellular nodule, which grows up into a leafy stem, whence is explained the extra- ordinary diffusion of these plants, even of such species as never bear fruit in particular localities. Schimper observed tins process on the rootlets of the Mosses, partly directly, partly after they had become converted into a green structure composed of confervoid filaments, resembling the proembryo; he found the same pro- embryo-like structure grow out from the leaf-cells of many species, (e. c/., OHhotrichum Lyellii), and confirmed what Klitzing had already seen, that even the cells of torn leaves will produce simi- lar growths under favourable circnmstanees In paiiicular cases also, compound organs (the leaves oi Mnium palustre^ M. anclTogy- num, the antheridia of Tetraphis pellucida, &c.) are developed into tuberous structures, spontaneously separating. From the fact that the cells of dijEfei*ent parts of the Mosses are ca- pable of becoming developed into a bud or a proembryonal confer- void structure producing a bud, it follows that in these plants, not- withstanding their already rather complex sti-ucture, the subordi- nation of the individual cell to the purposes of the whole is still but small, and that the individual life even here readily acquires the preponderance. But whether in the higher plants the individual cell is still capable of coming forth independently in an analagous manner and giving rise to the formation of a bud by development 106 ANATOMY AND PHYSIOLOGy OF of a cellular mass in its interior, or v/hetlier a complete group of cells must co-operate fiom the very beginning for the formation of the bud, we shall not be able to decide until we shall have traced back the normal development of buds to their first origin. If, however, it should be the case that the formation of a bud starts originally from a single cell, this is still incapable, in the higher plants, of forming a bud, when it is separated from the rest of the plant be- fore it has produced a new individual and this has grown up to a certain point of development, at the expense of nutriment pioduced by other cells. Therefore in all the more highly organized plants only organs of considerable size, composed of numerous cells and containing a certain amount of assimilated nutriment, are capable of laying down the foundation of a new plant. I have explained above, the doctrine that a branched plant is composed of as many individuals as it possesses ramifications. Taken stiictly, tins is not absolutely true, for a perfect plant pos- sesses not only an ascending axis, clothed with leaves, but a de- scending axis, a root. In many plants (in all leafy Cryptogamia, and in the Monocotyledons), even the primary axis is imperfect, for merely the ascending portion of it exists, while a primary descending axis is wanting, and is replaced by secondary axes which shoot out firom the lateral surfaces of the stem. The same incompleteness exists in every branch, it consists merely of an ascending axis, therefore corresponds simply to half a plant, as also each ramification of the root represents the corresponding half of a complete plant. Since, however, the individual parts of a plant very generally possess the power of producing that part of a complete plant in which they are deficient, when either a sufficient supply of nutri- ment has been stored up in their interier to last, or the requisite sustenance is still conveyed to them by the parent plant, until the completion is attained and they can prepare their own food inde- pendently, there exists, as a rule, little difficulty in producing a new individual furnished with all necessary organs, from a single part of a '|)lant. This is most readily effected with an ascending axis, since, on the whole, this is very prone to pioduce radical fibres from its lateral surfaces, and thus to become placed in a con- dition to sustain itself independently. It is more difficult to raise a new plant from a detached descending axis, since such a root is obliged to produce a leaf-bud, fi^om which the future stem has to grow up ; a reproduction which in general is much less readily effected than the formation of lateral roots fi^om an ascending axis. Finally even a detached leaf may give origin to the formation of a new plant ; in this case it must form both root and leaf-bud, to which, generally speaking, the leaves have but very slight tendency. The readiness with which both descending and ascending axes aie formed at places where they do not make their appearance in THE VEGETABLE CELL. 107 the natural course of vegetation, varies extremely in diflFerent plants, while at the same time we are unable to find a reason for this vaiiation in the organization of the particular species of plants ; in many species, for instance in the rooting of Caetese, Willows, &c., this development takes place so readily, that it can be counted on with the greatest certainty, while in others the development of the wanting organs, for example, of roots and still more of leaf-buds in Pmus, never or but very rarely occurs. In general the formation of the said organs takes place the more readily the richer the detached part is in parenchymatous cellular tissue, and the more assimilated nutiiment there exists deposited in it, at the expense of which it may be sustained until the organ necessary to make it a complete plant is formed ; but tliis rule is only valid for the extreme cases, and, mostly, we cannot say what is the reason, they are readily or not all inclined to such production. In very many plants, the formation of buds, which grow up into distinct plants, is a regular operation, independent of external causes. These frequently separate spontaneously from the parent in a rather rudimentary condition, ^d grow into independent plants subsequently ; in other cases, ^ch separation occurs after the parent plant is dead and decayed, through particular ramifica- tions of it remaining alive. In the plants having a thallus, we meet with the formation of shoots which have not the form of the ordinary branches, but in which the formation of the parent plant is repeated. Thus, in the Algse, new plants are not unfrequently produced, both from the ftond and from the disk-like base of this, or out of stolo- niferous prolongations of it In the Liverworts and Mosses it is a very general condition for single branches, the so-called innova- tions, to lepeat the form of the main stem, and when this decays, to appear as the stems of new plants. In the higher plants, ramifications very frequently occur, deviating in form from the ordinary leafy branches, and destined to serve for the multiplica- tion of the plant. They present themselves either in abbreviated and thickened forms (as bulbs and tubers), in which case they do not generally produce roots of their own untiL detached from the parent, or, on the contrary, they exhibit a predominant longitudi- nal growth (as runners or stolons above or below the surface of the ground), in which case, roots are developed, and they sustain themselves independently before their separation from the parent. The branches destined to the multiplication sometimes spring from the normal place, from the axis of a leaf (e. g., the bulbels of Lilium tigrinum) ; sometimes they originate from abnormal metamorphoses of flower-buds (the bulbels of the inflorescence of many species of Allmm, the tubers of Polygonum viviparwn) ; sometimes they break out, as the so-called adventitious buds, from spots which do not normally bear buds. The latter occurs 108 ANATOMY AND PHYSIOLOGY OF on the roots of a large number of trees (e. g.^ Poplars, Wild Cherries, Plums, &a), as well as on the leaves of many plants {e, g., As- pidiv7}i bulbiferuTYij Malaxis jpaludosa^ and Bryojphyllurn call-' , cinum). The pollarding of a plant frequently causes the development of shoots. The formation of roots generally takes place readily when the descending sap is arrested anywhere in its downward course by cutting through the baik, especially when, at the same time, light is excluded from the wounded spot, and this kept moist. In this case, the roots break out in most plants from the thickening which is formed at the upper border of the wound. On the other hand, the plant is caused to form leaf-buds in un- usual places when the whole of the leafy part is cut off; for then leaf-buds are formed beneath the bark, both on the lower part of the stem and on the roots, breaking through the bark, and grow- ing up into stems Most Dicotyledonous trees possess this power until they have attained too great an age, but most of the Coni- feise are devoid of it. This capability of foiming leaf-buds is so great in many plants, that every fragment of the root may be used for raising new plants from it, — for example, in the horse- radish, Madura aurantic^, &c. It is most difficult to induce the formation of buds on the leaves. Detached leaves have very great tendency to form roots, when they are placed in moist earth ; they afford, under such cir- cumstances, the peculiar example of a plant which fully exercises the functions of nutrition, but is altogether incapable of growth. Such rooted leaves sometimes attain an age far exceeding their usual period of existence; thus Knight, for example, saw the leaves of Mentha piperita, which he had caused to produce roots, maintain themselves fresla for more than a year, and assume almost the aspect of evergreen leaves (Knight, " Selection from the Physiol Papers/' 270). Growth into a new plant is only possible in such a rooted leaf when it developes a leaf-bud ; in general, this does not readily happen. There are plants, it is true, as already mentioned, on the leaves of which leaf-buds are regularly developed ; and a considerable number of plants have been noticed, on which buds had formed accidentally, on par- ticular leaves, still connected with the plant, e. g., Drosera, For- tulaca, Gardaonine pratensis^ Glechoma hederacea, &c. ; but, on the whole, these examples are rare. Buds are most readily formed on detached leaves when these have a fleshy consistence ; their development has been observed in particular on the bulb scales of Eiicorwis regia^ Lilium caoididum, Hyacmfmis, Scilla mari- tima, on the leaves of Ormthogalum thyrsoides, &c. ; moreover, not unfrequently on the leaves of different species of Crassula and Aloe, Buds are formed much less readily than on such suc- culent leaves, on leathery leaves,— for example, of Gitms, Aucuha, Hoya camosa, Ficus eladka, TheoihuisP^, &a, although these THE VEGETABLE CELL. 109 strike root freely (See " On some unusual Gases of Burl-forona" tion ;'' Mmiter, '^ObservatioQis on special Ppcidiarities on the Mode of Midtiplicaiion of Plants by Buds," — Bot Zeit 1845, 537, et s^q). A detached portion of a plant is not, lio^^ever, merely capable of producing the organs wanting to form a perfect plant, but it is also in a condition to become blended witli another plant, and lead a common life with it, on which capability depend the nnmerons garden operations whicb are known, under the not very apt name of " ennobling'' (veredeln, grafting). The conjunction of young, succulent parts, still in course of development, is a necessary condition of this blending. This condition is very easily fulfilled in Dicotyledonous plants, because there exists between the bark and the wood a layer of elementary organs in course of de- velopment, the so-called camblwin, and thus there is little diffi- culty in so uniting the two plants, that this layer, of both parts, meets at least at one point. But in the Monocotyledons, in which the vascular bundles lie scattered through the whole stem, and no definite cambium layer exists, the conditions are far more unfa- vourable. It is true, according to De CandoUe's account (" PhysioV ii. 787), the gardener Baumann, of Bollwiler, succeeded in grafting Draccena ferrea on Dr. teTininalis ; but the graft died after one year. But^the experiments of Oaldrini i^'' Ann, d, Sc. Nat!' Sone ser. vi. 181) on the grafting of Gi'asses, had a more favoui'able result, for he succeeded in gx-afting even species of different genera, e, g., Rice upon Panicum crus galli with success, a result which is explained by the fact that, in the Grasses the lower part of the internodes enclosed in the leaf-sheath remains for a long time soft and succulent. A second necessary condition of the blending of growth, is great similarity of the two plants ; they mxist not only be nearly allied botanically, but have a great agreement in the composition of the sap. OhsBT'v, 1. The possibility of grafting plants upon one another is de- t*ermined, ia general, by their systematic position, yet many anomalies occur. While it is usual that different species of one genus can be grafted upon one another, and in many cases it is even possible in species of nearly-allied genera, as, for instance, Pears on Quinces, on Gratmgus Oxya- ccmtha^ or on Amelanchier 'oulga/ru^ while Syringa vulgaris at least grows trary, in many cases an union, or at least the maintenance for a long endurance of the graft, cannot be secured, in spite of far closer botanical affinity, e. g., between Chesnuts and Beeches, or Apples and Pears. Ohserv, % The propagation by division is in many cases of the highest practical value. Although the case occurs here and there, that a parti- cular branch of a plant disagrees from the rest of the branches of the speci- men in certain small peculiarities of gxowth, the colour of the leaves, the doubleness of the fiowers, the character of the fruit, &c., possessing the 110 ANATOMY AND PHYSIOLOGY OF properties of a special variety, yet tHs is an exception to the rale Every part detaclied from a plant retains this agreement after its separation^ and thus propagation by division affords tlie means of mnlliplying certain varieties wHck could not, or only witli imcertainty, be propagated by seed. Cases certainly do occur in gTafted trees where the composition of the sap of the stock exercises a certain influence upon the characters of the fmit of the graft, but on the whole, this is an exception. (Gartner has given a comparative account of the observations on this subject, in lus ^^ JSxperi^nents andOhserv. on Hybridation'' — " Versuchen und Beohacht uh du Bastardhldiingp 606 ) h Fropagation hj Spores and Seeds, In all vegetables which attain their full normal development, the period of vegetation is succeeded by that of fiuctification, ■whether, as in the lower plants, the same cells which in youth executed the vegetative functions, in their subsequent period of life become organs of fructification, or, special organs of fructifica- tion become developed. Observ. The universality of this pro]3osition is truly only borne out by analogy with the majority of plants, for in the present condition of our knowledge we cannot determine whether all vegetables fructify. In many lower plants we are still unacquainted with any fructification, either be- cause they are really defi.cient in them, as may be possible for instance in the Yeast-plant, or that we do not know all the stages of their develop- ment. The latter is the case in many lower plants ; the difficulty of study- ing them is increased by the fact that a large number of forms have been described as peculiar species, especially among the Algse, wliicli are only earlier stages of development, and in many cases abnormal examples pro- duced by imfavourable external conditions of plants frequently belonging to totally different families. The organ destined for a germ may always Ibe traced back to an origin from a single cell. When this cell, at the epoch of its sepai^ation from the parent plant, contains no rudiment of a new plant, but only an organizable fluid, or, in rarer cases, a few secondary cells firmly blended with its membrane, and this cell, after its separation from the parent plant, under the influence of external circumstances favoxn-aHe to the excitement of vegetation, grows up directly into a new plant through expansion of its mem- brane and production of new cells in its interior, this is called a spore (spora, keimkoroi). The formation of spores takes place without fertilization, and plants wliich are propagated by spores are termed Gryptogawiia or Exemhryonaias. When, on the other hand, the propagative cell (as emhryosac) forms part of a compound organ, and through previous impreg- nation, produces in its interior the rudiments of a perfect plant, furnished with stem and root (the embryo, keim), and this becomes detached with the enveloping parts formed by the further deve- THE VEGETABLE CELL. Ill lopment of the ovule^ from the parent-plantj these envelopes to- gether with the embryo, are collectively termed the &eed, and the plants which bear seeds, Phanerogamia or E'inhryonatce. Ohserv. As will appear below, all the i>lants beaiing spores are not unisexual, but the impregnation in them standb in a totally different rela- tion to the production of the new plant, from what it does in the Phane- rogamia. In the latter, the formation of the embiyo is the immediate result of the impregnation ; when this does not take place, the seed cannot germinate. In the Cryptogamia, on the contrary, which have an impregnative process, neither the cell which forms the spore, nor the spore itself become impregnated, but this is formed and becomes capable of germination without a previous impi-egnation, and impregnating organs are found, sooner or later, upon a germ-plant, or pro-emh yo, growing from the spore, upon the action of which organs depends the development of the yet imperfect plant mto a complete vegeta]:>le. a PROPAGATION BY SPOBES. a. Propagation of Thallophytes. There is considerable variation in the modes of development of the spores in the different groups of Gryptogamons plants. It will not be without interest to take a brief glance at the principal modifications. In the Fimgi we are above all struck by the production of an enormous number of spores, so that in proportion to the great mass formed by the spores, and in the higher Fungi in propoition to the large sporangium, the vegetative part of those plants, the thallus, composed of loosely-connected filaments, and in most cases devoid of any definite outline, exhibits an inconsiderable deve- lopment. In the lowest forms of Fungi, the Coniomyeeies and Syjyho" Tnycetes, the formation of the spores, notwithstanding the innu- merable shapes under which these plants present themselves, is extremely simple, their production depending on a breaking-up of the fructifying part of the Fungus into its constituent cells, or into granules composed of several cells closely connected together; whence L^veilld says, correctly, that the Fungus consists, in its simplest form, of a simple or cellular filament terminating in a spore. When we come to the Mueorinece, we already find an advance, for here, as in Ascophora, the extremity of the filament expands into a vesicular cell, in the cavity of which a mass of spores are formed by &ee cell-formation. A similar origin of the spores is met with also in the higher forms of Fungi, in which, however, the single cell producing the spores no longer constitutes the entire organ of fructification, but large sporangia appear under the most varied forms, wherein the parent-cells of the spores are collected together in a definite layer, which sometimes lines the cavity of the sporangium, as in the OasUTomymtea, 112 ANATOMY AND PHYSIOLOGY OF sometimes forms a globular mxcleiis imbedded in the substance of the sporangium, as in the Pyrenomycctes, and sometimes appears as a membrane lying free upon the outer surface of the sporan- gium, as in Discomycetes and Hymenomycetes. In the higher Fungi, the number of spores formed in a parent-cell is definite, and we meet at once here that fixed numerical relation, which remains the same in the formation of the spores of the Ciypto- gamia and of the pollen-grains of the Phanerogamia throughout the whole Vegetable Kingdom, according to which, usually four, more rarely eight or sixteen, spores or pollen-grains are formed in a parent-cell, while tlie number may also sink on the other side to two or one. Among the Fungi, four spores are foimed in the majority of cases (in the IIy7)ienomycetes), sometimes only two or one in a cell ; in a few groups, as in the Tuheracem and Discomycetes, the number rises to eight (L(^veille, "Ri ch. s, Vhy- men, d Champign/' — Ann. cL sc. not. sec. sen viii. 321; Coida "^Icones Fungorum"). In regard to the form of the parent-cells, two modifications occur. In the Pyrenomycetes, Discomycetes, and Tuheracece, they appear as longish utricles (asoi), in the cavity of which the spores are developed by free cell-formation, after a previous production of a nucleus, and then frequently (e. g , Peziza) each spore again divides by a septum into two, sometimes even into more, cells. In the Lycoperdaceoe and Hymenomycetes, on the contrary, four (in rare cases only two, or one) protrusions of the wall of the parent- cell are formed, each of wliich becomes the seat of the production of a spore. These parent-cells are called hasidla. From the small size of the spores of most Fungi, it is not de- cided whether the cell-membrane of the spore secretes a special layer upon its outer surface in all cases (a kind of cuticle). In a ffreat number this may be easily perceived ; like the outer coat of loUeix-grams, it is frequently covered with reticularly connected ridges, little spines, &c. In germination, the coat of the spore ex- tends itself into a filament, which in the minute mildew-like Fungi is capable of growing on into a perfect plant. Whether this pro- duction of a new Fungus from a single spore occurs also in the higher Fungi, or whether the filaments which grow forth fi-om a number of spores germinating side by side, must become com- bined into a common tissue, has yet to be decided by observation. The latter is at all events a common process. (See Ehrenberg's ^' De mycetogenesi, Nov. Act Nat Out." x. p. 1, 161.) In the Lichens the fructification of many Fungi (Pezizece and Sphceriacece) is repeated most exactly. In the interior of the thallus is formed a gelatinous nucleus of elongated cells, converg- ing towards the central point, and embedded in an abundance of intercellular substance. A portion of these cells become tubular (asci or thecce) and produce the spores. In the naked-fruited Lichens the thallus opens above the nucleus, and the latter spreads THE VEGETABLE CELL. lis Fig, 49. out into a more or less flat disk (tlie thecal layer) ; in the covered- fruited, it remains enclosed in the thallus. In each of the parent- cells eight spores are formed by free cell formation, and in very many cases these form two, four or a greater number of secondary cells in their interior. Very few observations' have been made on the germination of these spores According to HoUe (" ZurEnt- wlckeliingsg, von Borrera ciliaris/' — On the development of 5. ciliaris, Diss. 1848, Gottingen), the secondary cells break through the primary spore cell as filaments, and are con- verted into cells outside the spore. According to Meyer's account (" Nebenstunden mein. Beschaftig- ung/' 175), the outer membrane of the spore is not torn, and when a number of spores germinate side by side, the filaments into which they grow out be- come blended together, and contribute jointly to the formation of a new plant. According to the observations of Tulasne (" Vln- stitut," No 849), the inner spore-coat, both of simple and compound spores, grows out into one or more filaments, which soon ramify and acquire septa, and whose short interlacing branches form little cushions, upon which little colourless cells accumu- late, and in which the green cells forming the rudi- ments of the cortical layer of the new plant, make their appearance. We meet with a far greater complication of phe- nomena when we look towards the spores of the Algse, even though here no co-operation of two sexes occurs. This latter may indeed seem doubtful in a number of Algas, in wliich a so-called coagulation occurs, but a more minute examination of this process shews that it bears no analogy to sexual reproduction. This conjugation presents itself most distinctly in the so-called GonjugatOB (the genera — Zygnema^ fig. 49, two ceiis of zy^^ — Tyndaridea, Mougeotia, Staurocarpus, &c.), in of'^Z^u^lml^ which it was observed first by Vaucher, The fila- ^j wS^foSfon ments of these Confervse lie parallel, side by side, <>f t^e conneotrngr 1 , . . ^ '^^ in branch ; b, con- or bent m a ziz-zag manner towards each other, n«ctrogTbwxch;c^ and send out from their cell-walls towards the ^^^^^' the nearest cell of the neighbouring filament, a blunt branch (a), which grows together with a similar and corresponding branch of the other cell coming to meet it, upon which the paitition in the cross-branch (b) becomes absorbed, and the solid matter of the contents of both cells becomes balled together into a mass in the cavity of one of them, or in the connecting branch, this mass ac- quiring a cellulose membrane, and in this way being converted into a spore (c). The following circumstances tell against this process being considered as an act of impregnation. The contents I 114i ANATOMY AND PHYSIOLOGY OF of the two cells are exactly similar ; sometimes all the cells of one filament take away the contents of the cells of the other ; sometimes this happens only to a part of the cells, while the rest empty themselves into the cells of the second filament ; and some- times spores are formed in cells which have not copulated, all this taking place v^ithont any definite rule. Copulation has recently been discovered in many uni-cellular Algge, in particular by Morren in ClosteTium {^^Ann. d,Sc. nat. sec. ser," V. 2 57), by Ealfs, in the Desmidiacese, and by Thwaites (^'Ann. of N'at Hist" XX. 9, S48) in the Diatomacese. Eemarkable as the whole process of copulation is, its product is, in many respects, enigmatical in no less degree. In the copulation of uni-cellular Algse, two new individuals are generally formed; thus there is no increase connected with this Biode of piopagation, but frequently only one new individual is formed, and thus is presented the strange phenomenon of a propagation resulting in a diminution of the number of individuals, since the copulating individuals die. In the Diatomaceae, moreover, ,the individuals produced by copu- lation are much larger than their parents. In the majority of copulating Algse, particularly in the Desmidiacese and Zygnemece,^ the spore produced fi:om the union of the contents of the two cells has not yet been seen to germinate, and it is not impx^obable that it ought to be regarded, not as a spore, but as a sporangium, that is to say, as a cell, the contents of which become developed into numbers of germs (See AgSuxdh, ^^ Ann., d. Sc.nat sec. Ser" m, 197; Hassall, '^Brit Fresh-water Algm,'' 24; Ralfs, ^'Desmidiece/' 10). In by far the greater number of the Algse, the spores are not formed by copulation, but in single cells, either, as in the lower forms, in the vegetative cells towards the close of their existence, or in special fructification cells. The spores of a very large number of Algse, either before their exit from the parent-cell, but principally in the period just succeed- ing the emission, exhibit a movement, which is often very rapid. These movements have not unfrequently been taken for animal, voluntaiy motions, and have given origin to the most fabulous conceptions concerning the transformation of animals into plants. We owe the first extensive and aecm-ate observations on these moving spores to the younger Agardh ("Ann. d. Sc. nat sec. Ser!' vi. 193), who called them Zoospores. According to his researches, they occur in the N'ostocJdncce,OscillatoricB, OonJ-crvece, Conjugatce^ EctocaTpcm, Ulvacece^ and SiphonccB. The following is his account of their development. During the later periods of the growth of the cells, the chlorophyll, which in the young cells of these plants forms a homogeneous mass, becomes transformed into globules, which towards the close of the cell's life assume a spherical shape, become detached from the wall of the cells and balled together in * Erroneous in regard to Zyncmese, see Yaucher, Meyer, and, more recently, Fringsheim. Flo'ia, Aug. 1852 — A, H. THE VEGETABLE CELL. 115 a globular lump in tlie middle. A " swarming " now begin^. to be evident in this mass, the granules become isolated, and swim about the cavity of the cell. A papilliform protuberance is after- wards produced from the cell- wall, wliich tears at its apex, and the spores making their way out by tliis orifice swim about in the surrounding water. By degrees they begin to withdiaw towards the darkest part of the water, become attached to any solid body, and begin to germinate, by an expansion of their membrane. A2:ardh observed a transparent process (beak, Schnabel) at that en^d of theBe spore, wldf .Iwa^s went' first' in the mLznents. But the true organ, on which this movement depends, is not this beak, which itself is motionless, but, as Thuret fir^t shewed (''Ann. d, Sc. nat sec. 8er/' xix. 266), there exist at the brighter coloured end of the spore, cili^ of various lengths moving rapidly, and by their vibrations causing the motion of the whole spoi^e. The number of these ciliae differs in different genera. Thuret found in Conferva glomerata (see tab. 1, 23, 24,) and Twularis, two cilise on each spore, in Ghoetophora elegans four, on the spores of Prolifera a circle of very numerous cili^, (see tab. 1, 19 — 22, which represent the spore (19) and its first stages of develop- ment, after Thuret); subsequently (''Ann. cL 8g, nat Sme. Serf iii 274) he made known that the spores of Ectocarpus have two, those of Ulva and Enteromorpha four ciliss. These observations obtained full confirmation by othei*s, especially by Fresenius ("Zur Gontrov^ UK die VerwandL von Infus. in AlgenJ, and by Alex. Braun (repeated by Siebold, ''^An7h. d. 8c. nat Sme. Ser, xii 151). The opinion that these spores possess animal life during the period of their movement, and become plants at the moment of germination, does not, however, depend merely on a confusion of their movements with the voluntary motion of animals^ but derives an apparent confirmation fi^om the fact that in very many cases each of these spores contains a red spot (according to Nageli a red oil-dxop), which was taken for an eye by Ehrenberg and others. Even before Thuret had made known his observations upon the organs of motion of the zoospores, Unger ("Die Pjianze im Momente der Thier-werdung") had published very minute observations upon the formation and motion of the very large spores of Vaucheria. In Vaticheria^ the single granules of chlo- rophyll are not developed into minute spores famished with a few cilise, but the entire mass of chlorophyll of the terminal joint of a filament, or of globular protuberances seated upon lateral branches, after being separated from the contents of the rest of the fibre by a septum, becomes balled together into one common spore, which makes its way out by a slit in the cell-membrane and ex- hibits rapid advancing and twisting movement. It is covered all over with countless vexy short eilise. The whole of the forma- tion of the spore occurs early in the morning, its exit from the parent-cell usually takes place about 8 A M., and after its motion I 2 116 ANATOMY AND PHYSIOLOGY OF lias endured for lialf-aii-hoiir, or at most two hours, it comes to rest, tlie outer coat covered with cilias, disappears veiy rapidly (by deconiposition ?) and germination commences by the coat of the spore growing out into a filament. Observ. — These observations first demonstrated the existence of cilise in the Vegetable Kingdom. It may be distinctly seen in Vaucheria that they do not belong to the cell-membrane (spore coat), but to a mem- brane clotLing tills. What the corresponding condition is in the zoospores, is as yet unexplained, since a membrane enveloping the whole spore has not yet been observed in these. Perhaps this may arise solely from the small size ol the spores and the tennity of their coating membrane, per- haps, however, the coat only exists locally aronnd the beak and the points of inbertion of tbe dim. Mettenins, indeed (^^£eUmgezur. Botanik,'' i. 34), assures us that the cibse are in connexion with the contents of the spores, but he has not offered sufficient evidence of this. When we compare these motions with the ciliary phenomena of animal cells ,and with the motions of the seminal filaments of the higher Cryptogamia, no doubt can remain that the movements of the cilise are the cause and not the effect of the movement of the spore, as l^Tageli {^^UnicellulaT Algm^^' 22) beheved; an opinion against which V. Siebold has already declared. The action of poisonous substances, such as alcohol, opium, and iodine, immediately arrests the motion. It appears possible for the formation of zoospores to originate from one single granule of chlorophyll, while in other cases, where only one or few spores are developed in a cell, (e, g. JDrapamaU dia, GhcBtophoTo), perhaps larger sections of the mass of chloro- phyll, or even the primordial utricle, by becoming constricted into separate segmenta, are the parts concerned in the formation of the spores. The actual conversion into a spore is not accurately known in its intimate processes, but must consist essentially in the formation of a cellulose membrane around the chlorophyll granules. It has already been remarked that in Vaucheria the whole mass of chlorophyll of a cell becomes coated with a mem- brane. Intermediate forms between these two extremes are met with, thus Saulier {^^Ann, d. Sc. nat Sme. Ser/' vii. 157) found in the genus Derbesia, very closely allied to Vaucheria, that neither tlie entire mass of chlorophyll collected into one spore, nor did its grains remain isolated, but separate groups, each com- posed of hundreds of grains of chlorophyll, became gathered up into globular masses, acquired a membranous coat and formed a short beak and a circle of cilige upon the surface."* Unger ("im- mosa/' 1848, 129) observed a perfectly analogous formation of the spores of Achlya prolifera^ which^ according to Thuret (''Ann. * See further on this subject, Thuret, ^^Ann, des. Sc. nat. 3 JSerJ' torn, xiv. and xvi. ; Cohn on Rcematococcus, Nova. Acta. vol. xxii., and on Stephanospho&ra, ^' Armals of Nat HisV Oct. andlSTov. 1852. — A. Braun. " fleh. die Verjwngung,'^ Leipzig 1851. The active zoospores have no cellulose membrane when first set free. — A. H. THE VEGETABLE CELL 117 d. Sc, nat 3^}i'3 S&r.^' iii. 27:1^); likewise possess a circle of very niiinerous cilifB. Whether, as Agardh assumedj the power of motion in the spores of the lower, and the want of it in those of the higher Algae (the GermTiiecBy Floridece, and Fucacece) warrants a rigid division of these plants into two sections, appears very doubtful, for accord- ing to Decaisne and Thuret {"Ann. d. Sc. nat Sme Ber!' iii 10) not only do the spores of the Fucacese present the same coat covered with short cilise as those of Vaueheria, which, however, either from the size or some other cause are motionless, but there also occur in the Fucaccss small moving spores bearing two cilise, enclosed in special cells, sometimes on the same plants that produce the spores, sometimes on distinct specimens. The said observers, indeed, have not recognized them as spores, but interpreted them as seminal filaments, but they have not the least resemblance to these, while they agree with the zoospores in form and in the pre- sence of a red point, the so-called eye. It is truly a remarkable circumstance tliat one plant should bear two kinds of sjpores, dif- ferently formed, but the same occurs again as an universal rule in the OeramiecB and Floridsce, for these plants bear not only the generally recognized spores, and gemmse testifying their nature as such by generation, which originate, like pollen-grains, in a parent-cell dividing into four chambers (the so-called tetra- spores)^ but other spores also, which are not produced in fours in a parent-cell, and are contained in variable numbers in fructifica- tions of the most diverse shapes (oapsula^ glomeruli, favella, frc). The spores of this second kind germinate, as Agardh has shewn, like the tetraspores, their membrane extending itself on one side into a root-like prolongation, on the other into a filament whieli divides into cells, and grows up into a pi mt. Decaisne and Thuret observed a most peculiar circumstance in the spores of man^ Fucoideje ; namely, the spores had not com- pleted their development at the time of their maturation and de- tachment fi:om the parent plant, for, after this, commenced a divi- sion into the proper germinating spores (in Fucus serratns and vesieulosus into eight, in F, nodosus into four, in F, eanalicu- latus into two secondary spores). Martins thought he had found, in the spores of Fueus, that the separate spores did not grow up into new plants, but as in the Fungi, a number of germinating spores became conjoined to form one common plant. This has been sufficiently refuted by Agardh, Decaisne, and Thuret. The spores of the Fucoideae germinate like those of all other Algae, by expansion of their internal coat on one side, into a root-like fibre, on the other into a filament which becomes subdivided into cells. ** Propagation of the Gryptoga/mB having Stern cmd Leaves. While in the three families of Oryptogamia possessing a thallus (with the exception of the Charas, to be mentioned presently) all J 18 ANATOMY AND PHYSIOLOGY OF attempts to discover male organs has proved the more vain the further the investigation of these plants has advanced, in the more highly organised famihes of Cryptogamia, on the contrary, in which there exists separation of the organs of vegetation into stem and leaf, the last few years have seen the discovery of convincing proofs of tlie existence of two sexes. In the last century, when Hedwig in particular devoted himself to the investigation of the Cryptogamia, the idea that two sexes must exist in all Cryptogamous plants, was quite predominant; and thus, often enough without a trace of consideration, the most diverse parts were, from mere opinion, separated as male organs. This brought the whole effort to discover impregnating oi'gans into discredit, and the opinion that all the Cryptogamia were de- void of male organs, and developed their spores without previous impregnation, became more and more diffused. It is true that organs had been discovered in certain Cryptogamous families, espe- cially the Charas and Mosses, which from the time of their appear- ance, from their position, «fec., stood in evident relation to the fruit; but since no positive influence could be proved to be exerted by them upon the young sporangia, their function as anthers was denied ; although it was at the same time admitted they had a ceitain analogy with them, whence they were, indeed, called an- tluTidia. In more recent times, two circumstances seemed chiefly to strengthen the earlier doubt which had been entertained as to the function of the antheridia. My own researches, namely, shewed that the spores of the higher Cryptogamia do not, as had been previously supposed, exhibit a resemblance in respect to their development and structure, to tJie seeds of the Phanerogamia, but that the most perfect agreement exists between them and the pollen-grains of the Phanerogamia. From this it necessarily, yet strangely, appeared that organs of perfectly like structure fulfilled the fanction of germs in one part of the Vegetable Kingdom and in the other part constituted the male, impregnating organs ; but, little as the formation of a pollen-grain depends upon an impregna- tion, no one circumstance shewed itself in the development of the spore, at all more resulting from the co-operation of an impreg- nating organ. Stni more doubtful did the theory of the impreg- nation of the Cryptogamia necessarily become^ when Nageli made the discovery, in the Ferns, of antheridia in many respects resem- bling those of the Mosses, which were not formed upon the fall- grown plant at the same time as the rudiments of the sporangia, but occurred upon the germ-plant (pro-embryo), while the perfect plant was devoid of them. Under these circumstances, Schleiden seemed to be warranted in characterizing the effort to discover impregnating organs in the Cryptogamia, as a mania. But by good luck, certain men who had this mania did not allow it to lead them astray in their researches, and a^ often happens, nature this time proved so rich THE VEGETABLE CELL. 119 that, not indeed was what had been nought found, bnt instead of this a series of conditions, the existence of which was previously altogether unsuspected. The researches relating to this point are, it is true, still far from their completion, since at the present moment nothing more than a preliminary notice of isolated con- clusions already arrived at can be given ; but these, although isola- ted, cause us to expect with certainty in this field a series of the most striking discoveries. The Mosses have served for a very long period as the main props of the view that two sexes and an impiegnation occur in in the higher Cryptogamia. Not only was attention naturally called in these to the constant occurrence of the antheridia, and their great development, but trustworthy experience, formerly of Bruch, more recently of Schimper {^^Rech. s, I. Mousses!' 55) de- monstrated that Mosses which have antheridia and the rudiments of sporangia upon the same stem always bear fruit, while dioecious Mosses never setfruit in localitieswhere only female specimens grow. No one has succeeded in making out the mode in which the anthe- ridia act upon the rudimentary fruit ; but the physiological fact just mentioned does not lose its force on that account. A second family indicating the necessity of an impregnation, were the Rhizocarpe^, since numerous observations had shewn that the large and small spores of these plants could not be separated without preventing the former growing into new plants. Schleiden, indeed, had extended his theory of the development of the embryo from the pollen-tube to this family, and arranged them with Phane- rogamia. But nothing was gained by this, for, on the one hand, Schleiden's whole theory of impregnation proved a false beacon ; on the other, Schleiden's statements as to the Ehizocarpese were not confirmed, and tliis more particularly in the most essential point, the mode of origin of the embryo. Then unexpectedly appeared Count Leszcyc-Suminski's essay on the development of Ferns (''ZuTEntwicJdungsgesGLdeTFarreyi' krauter," 1848), the contents of which at first seemed fabulous, so contradictory were they to all that was known of the organization and development of plants. But a more minute study of this treatise — a comparison of the autho/s results with nature — soon shewed that although he had been deceived in a few particulars, his ac- count was far fi:om being a creation of the fancy^ and that his re- searches had broken open a path to a long series of discoveries- In all families of the leafy Cryptogamia (with the exception of the Lycopodiacese*) antheridia have been discovered, exhibiting it is true considerable variations of external forra and structure in the difierent families, but collectively agreeing in the circumstance of developing in their interior very delicately-waUed cells, at first containing an amorphous substance coloured yellow by iodine, in place of which, at the epoch of maturation of the antheridia, a d^eli- * Now found in these also, see note further on. — A. H. 120 ANATOMY AND PHYSIOLOGY OF eate filament presents itself, displaying several spiral convolutions, tliickened at one end and running off to a very fine point at the other. Tlie filaments manifest lively motions, exhibiting differences accox'ding to the manner in "which they are rolled up, in some cases while still enclosed in the cells -where they are developed, but more particularly after they have emerged into the water fi^om antheridium, which opens when ripe. Thus, when the filament is rolled up like a watch-spring, the motion is more or less rota- tory, but if it is coiled over in the form of a cork-screw, the move- ment is at the same time an advancing one. In these movements the thin end of the fibre almost always goes first. Minute obser- vation, which in many cases is very difficult, both from the rapi- dity of the motion (which, however, is readily arrested by poisons), and the great delicacy of the whole structure, shews that the movements arise from extremely delicate and comparatively long cili^, of which two are usually found at the thin end of the fila- ment, and which only seem to occur in larger numbers in the Ferns. The filament itself exhibits no independent motion, as indeed, altogether, the land of motion does not indicate any will. The term seminal filaments has been not inaptly applied to these filaments. Ohserv, The first observation on the motion of the contents of the antheridia was made by Schmidel ('^ Icones plantarum,^' 1762, 85) in Jun~ germannia pusilla. The imperfection of the microscopes of that period, however, seems to have prevented Ms seeing the seminal filaments, and he probably only observed the cells in which the filaments were enclosed. The same seems to have been the case with the observations made by Fr. Kees von Esenbeck ('^ Flora" 1822, 1, 34) in the antheridia oi Sphagnum. He considered the moving bodies which he saw to be globular monads, and did not doubt their animal nature. The spiral filaments themselves were discovered by linger in the Mosses and Liverworts (" Ann, cl iSc. nak % S&T^ xi. 257) ; in accordance with the then prevalent notions on spermatozoa, he regarded them as animals, and applied to them the name of Spirillvm hryozoon. Recent years have scarcely added to his observations on the seminal filaments, more than the fact that two cilise exist at the thin end of the filameijts, which linger had overlooked (Be- caisne and Thuret, ''Ann, d. So. nat. 3, Ser'' iii 14). Plate 1, figs. 2% — 28. Seminal filaments of Sphagnmn; ■G.g. 26, represents two anther-ceUs with the seminal filaments enclosed ; fig 27, one of the latter seen fi-om the side (from linger). To me the filaments appear to have the form which I have represented in ■B.g. 28, The structure of the Moss-anthers is very simple. It consists of a simple sac, with a wall composed of a single layer of cells, which, according to linger, are applied upon the outside of a large cell, while according to ScMmper they are enveloped on their outer sides by a continuous mem- brane composed of intercellular substance. When mature, this coat is torn at the apex, and the contents, now dissolved into a mucilaginous fiuid, issue from it. The anthei^s of the Liverworts possess a structure completely analogous to that in the Mosses (Gottsche, ''Act Acad. Nat Cur.^' xx. 1, 293), THE VEGETABLE CELL. 121 only the wall of the sac, at all events iii many species, is composed of two layers of cells. The anthers of Chara, of wliicliFritzsclie (" Ueher den Pollen^'' G) lias given the most accurate description, poshess a highly complicated structure. Into the globular cavity enclosed by the eight cells containing red-colonred gra- nnies, projects a flask-shaped cell, almost as far as the middle; from its apex run out a mass of fine confervoid filaments, which are divided up very closely into joints, and in each of the cells is developed a seminal filament. The existence of an ii fusorial motion of these filaments was observed by Bischoff (" Cryptog Geirr 1, 13) ; their exact form (plate 1, ^g. 25, from Thuret), and the two cilise, by which they approximate closely to seminal filaments of the Mosses, were first made out by Amici (whose essay on this subject has not been printed) and Thuret (" Ann. d. Sc. nat. 2 /S'er." xiv., 66). In the Ferns the most different parts had long ago been interpreted, without any judgment, as male organs, even the stomates of their leaves, the annukis of their capsules, &c., when Nageli ('^ Zeitschr f. Wiss. Bot'' 1, 168) made the unexpected discovery that antheridia containing mov- ing seminal filaments, occur upon their pro-embryo. This was contrary to aU theory, yet as the observations of Thuret (" Ann, d. So. nat 3 /S'er.'* xi. 5) and Leszcyc-Suminski shewed, nevertheless proved well founded. The structure of fche antheridia of these plants bears a considerable re- semblance to that in the Mosses ; they are composed of a pedicellated cell, in the cavity of which is formed a second cell, fiUed with the small cellules containing the spiral filaments. The entire organ bursts at its summit, and extrudes its mucilaginous contents enclosing the seminal filaments. The latter are ribbon-like and flattened down, possessing, according to Suminski (plate 1, fig. 29) about six, according to Thuret numerous cilise. Schacht (" Linncea,'' 1849, 758, (fee.) agrees with the last statement, and states that the cilise are attached upon the narrow curves, and not on the thick end at the widest curve of the filaments. Thuret found the same organ on the pro-embyi'o of the Equisetacese. The last Cryptogamia on which the spiral filaments have been found are the Ehizocarpeae.* "N'igeli ('' ^eitschr f. Wiss. Botanik" iii. 199) suc- ceeded in finding them in Pilularia. The pollen-grains (smal spores) undergo a change after they have been discharged from the anthers, by the inner coat bursting the outer, and afterwards tearing, itself, to emit minute cellules which are filled with mucilage and starch. In these minute cells a vacant space is subsequently formed at one end, in which appears a spiral filament, turniag round and round, and leaving the cell the thin end foremost. The same phenomena have been observed by Mettenius in Iso'etes ("Beitr. z. Bo€' 1, 17). Thus have antheridia and sSminal filaments been found in all the leafy Cryptogamia, with the exception of the Lycopodiacese.t Whether semi- nal filaments occur in any other of the Thallophytes besides the Charas, remains to be seen. It is true that Nageli (" D-ie neuer Algensysteme,^^ 1 d>6 ; ''Zeitsckf. Wiss. BotJ' iii. 224 ; '' Bot Zeit:' 1849, 572) has stated that antheridia occur in the Eloridese, the essential parts of which consist of * + Hofmeister {^^FrucMbildung^Keimungy Sc.,der Cryptogamen,^^ Ldpz., 1851) has since shewn that the small spores of Selaginella produce seminal filaments, exactly in the same way as those of Isoctes. — A, H. 122 ANATOMY AND PHYSIOLOGY OF cells l-900tli of line in diameter, -with a scarcely visible spiral filament within ; but it maj l)e permitted, considering tlie difficulty wbicb bucli minute size of the organ opposes to observation, to doubt, with Mette- nius, whether there are really seminal filaments.^ The uniformity of the seminal filaments contained in the an~ theridia of the leafy Cryptogamia, leaves no doubt, in spite of the difierence of structure as above described, that these organs are of the same physiological nature. The circumstance, however, that these organs present themselves at such different stages of deve- lopment of the plants, must appear in the highest degree surpris- ing and indicative of altogether unlooked-for differences in the propagation of these vegetables. From the study of the Phanero- gamia, we are accustomed to regard the organs of fructification as the last stage of vegetable development, since their formation puts a period to any growth of the vegetative axis, and the maturation of the seed frequently involves the death of the parent organism. We meet with the same condition in the Mosses, in which the an- theridia and the rudiments of the sporangia are developed at the same time, the full development of the fruit succeeding the ripen- ing of the anthers. In the Ferns, on the contrary, the condition is diametrically reversed. The development of the sporangia fol- lows the usual law, but the formation of the antheridia takes place upon the pro-embryo after the spores have geiminated, never to be repeated in the plant growing up from the pro-embryo. In the Ehizocarpese, finally, the cells which enclose the seminal filaments are first developed after the pollen-grains (small spores) have been shed ; they are as it were dioecious plants, in which only the fe- male plant arrives at pei^fect development, the male being arrested at the stage of a germinating pollen-grain, which only produces seminal cells, and then dies. Before I pass to the consideration of the female organs of fructi fication of these plants, it will be necessary to speak of the spores and their development. I have already indicated that the spores of the higher Crypto- gamia agree completely with the pollen-grains of the Phanero- gamia in resjard to their development and structure. Not only m a portion of the Cryptogamic families, namely in the Equise- tacese, Ferns, and Lycopodiacese, does the sporangium fully agree with the theca of an anther in morphological respects (" Morph BetracM, des Sporang, d. ^m. Oefdss^ verseh Kryptog.^' — Mohl " Verm SchHft/' 94), but the development of the four spores in a parent-cell, and their structure, as has been more minutely pointed out above, are completely in agreement with the development and * The recent observations seem to indicate the existence of sexes in the Lichens, (^' Itsigsohn'' — JBot. Zdt 1850,51), and the 'Emxgi {^^ Tidasne, Go'iwptes rendusy' 1851, Berkeley and Broome, '^ Brit Association^'' 1851.) — A. H. THE VEGETABLE CELL. 12S structure of tlie pollen-grains. Just as the latter are developed in the anther without the co-operation of another organ, does this occur also in the spores. In certain Cryptogarnia (the Rhizocarpese and Lycopodiacese) we find the joeculiar condition, that spores of two kinds are developed simultaneously, in a wholly analogous manner in parent-cells, in capsular receptacles of two kinds, the spores larger and smaller, possessing exactly the same structure, except that one kind are larger and have a tougher outer coat. But in the Rhizocarpese, only the larger exercise the function of spores, the smaller, as above stated, developing the cells which contain seminal filaments ; in the Lycopodiaceoe, on the contrary, both kinds of spores produce plants.* The germination of the spores is as little dependent as their origin upon a previous impregnation derived from the antheridia, unless perhaps this be the case with the Charas, in which the Fig. 50. Fig, 51. Pro-embryo of Funaria hyqrometrica (according' to Young pro-embryo oiPteris ser Sehimper) a,rudunent of a bud ; &, a young stem ; c, first rulata according to Leszcyc-Su- development of the pro-embryo from tbe spore ; d, deve- minski. lopment further advanced. relation of the antheridia to germination is altogether unknown- In germination (except in Ghara) the spore does not grow at once into a plant like the parent, but is first developed into a thallus-like, cellular structure, totally devoid of vascular bundles, the so-called pro-embryo, which appears under very diflEerent forms in different plants of these tribes. In the Mosses (fig. 50) it pos- sesses the fonn of a branched Conferva, in the Ferns (fig. 51) the shape of a cordate leaflet not tinlike a frondose Liverwort, in the "* All error, See page 121, note; also Beporb on the Reproduction of the higher Cryptogarnia, by A. Henfrey. " Tram. BrU. Assoc.'' 1851. — A. H. 12-i ANATOMY AND PHYSIOLOaY OF Eqnisetacese of an irregular mass of cells divided into many lobes. The development of tlie pro-embryo is extremely simple in these plants. The spore-coat (fig. 50 c. d.) becomes expanded in germi- nation, bursts througli the outer membrane of the spore, sends out hair-like prolongations serving as rootlets on one side, and becomes prolonged on the other into the form of a cylindrical cell, which becoming divided by septa into a number of cells, and so on by continued growth and cell-multiplication, is gradually developed into the perfect pro-embryo. In these plants no part of the spore seems to be pre-determined for the production of the said parts, but every point of it to be cajDable of the development described ac- cording to the position in which it may be placed. But the germination of the large spores of Lycopodium, Mar- silsa, Pilularia, Salvinia, and Isoetes, is more complicated ; in them not only is that part of the spore, which by the contiguity of the four cells in each parent-cell, has acquired a more or less evidently three-sided pyramidal form, the only germinal point of it, but the pro-embryo is developed up to a certain stage in the interior of the spores, and issues from the rent in the outer spore- coat, as an already parenchymatous structure, of diflEerent form in different genera. The pro-embryo of the Mosses is capable of transforming one or more of the cells seated upon its various ramifications, immedi- ately into buds, which grow up into leafy stems, so that here we have the peculiar condition of one spore giving rise to the deve- lopment of a number of plants. The pro-embr3^os of Ferns, Ehizosperme^, Equisetacese, and Lyco- podiacese, on the contrary, are incapable of the immediate produc- tion of leaf-buds, and produce upon the uppermost layer of cells, one, or mostly a number of peculiarly-formed organs, which, fol- lowing the example of Leszcyc-Suminsld, are called ovules, from whicli organs, but not until after an impregnation by the anther- idia, which discharge their contents at the same time, the future plant gi'ows out under the form of a bud ; when this impregnation fails, tlae pro-embryo remains infertile. In the Ferns and Equisetaeese the pro-embryo produces the an- theridia with the ovules, at the same epoch ; in the Bhizocarpese, on the contrary, the parent plant which furnishes the large spores, forms at the same time smaller, for the purpose of producing an- theridia, and these small spores, as already mentioned, in like man- ner exhibit a kind of germination, the product of which consists not of an embryo, but of antheridial cells. In the Lycopodiacese the conditions are still obscure, (8ee note p. 121.) The ovule consists of a large cell belonging to the tissue of the pro-embryo, with four cells or rows of cells overlapping it on the outer surface of the pro-embryo, and leaving an intercellular pas- sage between them leading down from the open air to that cell. ' Count Leszcyc-Suminski, the discoverer of these ovules in the THE VEGETABLE CELL. 125 Ferns, observed the penetration of the spiral filaments into the canal just referred to. His idea that he saw the lower part of a spiral filament become transformed into the embryo, is doubtless the result of a mistake, readily to be pardoned in such difficult investigations, which does not damage the discovery we owe to him. There can be no doubt that in the rest of the plants under consideration, the spiral filaments are the bearers of the impreg- nating substance, since in the Rhizocarpeee, the spores which are allowed to germinate separately fi-om the small spores producing the spiral filaments, are capable indeed of forming a pro-embryo, but not of producing a plant fi:om the ovules of this. The plant, which is developed in the lower cell of the ovule, is organically connected with the pro-embryo ; it is a bud growing up from it, so that the leafy stem thence produced has no primary descending axis. (An error ; see p. 137 — ^A. H.) According to Hofmeister's researches, the relation of the anthe- ridia of the Mosses to the rest of the plant is again different. It has long been known, as already mentioned, that the rudiment of the fruit of these plants remains undeveloped when no antheridia are produced. This is explained by Hofiieister's investigations ; according to these, the rudiment of the fi:uit of tlie Moss (the so-called archegonimn) greatly resembles the ovules of the Ferns, since underneath the so-called style, lies a large cell, which by subdivision is converted into a cellular body, growing down- wards and becoming blended with tlie stem at the one end, and becoming prolonged upwards, and developed into the sporangium at the other. So that while in the Ferns, &c., the spore only forms the pro-embryo without impregnation, and the impregnation is necessary for the development of a leaf-bud, which grows up into the leafy stem forming the sporangia, the spore of the Mosses forms the pro-embryo and the leafy stem without impregnation, and this operation only causes the development of the spore-producing pa^-t of the plant (see W. Hofineister, ^'uh d. FruchtbilcL unci Keimung d. hoh. Kryptog" — Bot Zeit 1849, 793; Mettenius, ''Beitr, z. BoV 1. (Also "EoimeisteVy'^FTUGhtbildung, Keimung, <&g., der Gryptogamen" 4ito, Leipzig, 1851; and Henfrey^'s Report in the Transactions of the British Association, 1851; and Memoir on the '^Beproduction of the Higher Cryptogamia/' &c. — ^'Ann. of Nat History,'' sec. 2. vol. ix., 1852 — ^A. H.) 5. PBOPAGATION" BY SEEDS. Proceeding to the theory of the impregnation and the formation of the embrj-oin the Phanerogamia, we arrive upon ground which has been levelled by the researches of the last ten years. In no part of our science has careful investigation, penetrating with un- tiring patience into ultimate details, yielded more brilliant results, yet in no other part have the hardly-earned facts been so violently opposed, the conclusions, safely established, being even still contin- ually called in questiou onthe strength of superficial investigations. 126 ANATOMY AND PHYSIOLOGY OF Observ, As the minute exposition of tlie historical development of the theory of the sexes of plants would occupy far too large a space, an indi- cation of the mam points mu.&t suffice. Although the cultivation of many monoecious and dioecious plants might have led, even m ancient times, to the idea that plauts were fui-nished with sexual organs of two kinds, this ti'uth was not recognized until towards the end of the 17th century. First announced m England by Grew, Eay, and others, this theory obtained its first scientific establishment from E. J. Camerarius of Tubingen (''Be seoou plantarum epistola,'' 1G94); but it was Linnaeus more especially who securely established this new theory by his researches, and gave it universal diffusion by the preponderating influence he exercised in Botany, and by the displacement of all earlier systems by his Sexual System. When, finally, Kolreuter, succeeded by a longer series of experiments in demonstrating the possibility of producmg Hybrids in the Vegetable King- dom (" Vorlauf. Nachricht einig. d. Geschlecht d Pflanzen letreff. Versuche" 1761 — 1766), the theory of the sexuality of plants was as firmly establish- ed as it could be without a knowledge of the changes which the pollen- grains undergo upon the stigma and the processes occurring in the ovule. The last century did not essentially advance further in reference to this point. The excellent researches of Malpighi, if not forgotten or mismiderstood, were at all events not completed ; as to the structure and characters of the pollen and as to its relations to the stigma, numerous in- correct observations were published. "With this imperfect knowledge of the processes occurring in the interior of the ovule, it might easily be thought possible that fertile seeds should be perfected, at all events, in particular cases, without the co-operation of the pollen, and a number of observations were made known, partly in favour of such exceptional cases, and partly with the object of refuting the entke theory of the sexes of plants } thus Spallanzani and others asserted that female specimens of Hemp, Spinage, &c., had borne fertile seeds; Henschel beHeved that road-dust, powdered charcoal, sulphur, &c., might be substituted for the pollen ; Schultz stated, as the result of his observations, that the pollen need not necessarily come in contact with the stigma, but might impreg- nate from a distance by an aura seminalis ^ and Lecoq thought he had found that fertile seed might be developed without application of pollen to the stigma in monocarpic, but not in polycarpic, plants. The doubts thus excited were set at rest for ever by the brilliant discovery of Amici, that the pollen- grains germinate upon the stigma and that their internal coat grows down in the form of a tube through the style into the ovary, and comes into connection with the ovule (1823 — 1830) ; a discovery to which Gleichen had already come very near, but had not properly followed out. The universality of this process has indeed been denied, l3ut day by day the opposition becomes more completely silenced. Parallel with the researches on the structure of the pollen and its relation to the stigma, went the investigations on the ovule and the origin of the embryo, which had been taken up again from the last-mentioned period by Treviranus, and subsequently carried out fui-ther by Eob. Brown, Brongniart, Mirbel, Schleiden, Hofmeister and others. In the midst of this new development of the theory of impregna- tion, not the sexuality, but the respective import of the sexual organs, was unexpectedly called in question, by Schleiden stating that he had disco- THE VEGETABLE CELL. 127 vered that the embryo was not the product of the ovule, but originated in the tube growing into the ovule from the pollen-grain, whence the pollen- grain wab to ]>e considered as the true ovule, the plants hitherto regarded as male as the female, and vice mrsd. Here agam it was Amici, who by decisive observation solved the doubts arising out of this theory, and de- monstrated the new doctrme to be false, a result which soon obtained full confirmation from other investigations, especially from the extensive ob- servations of Hofmeibter and Tulasne. ■* The Pollen. As ilie development and structure of the pollen-grains have already been spoken of in tlie acconnt of the development of cells, I shall confine myself here to a few remarks upon this organ. The perfect pollen-grain consists of a cell, usually roundish or elliptical (elongated into a filament in Zosteo'o), which, excepting in certain water-plants, is coated on the outside by a membranous layer, which owes its origin to a secretion, and, in paiiicular cases, is separable into two or three superincumbent layers. The outer- most membrane, corresponding to a cuticle, is mostly rather tough, uniform, or covered with granules, spinules, projecting linear and often reticulated ridges, mostly coloured, and the seat of a more or less abundant secretion of a viscid oil. The internal coat is a co- lourless, uniform, soft, and extensible cellulose membrane. Its ca- vity is filled with a viscid fluid, rich in protoplasm, sometimes transparent, sometimes rendered opake by granules swimming in it (fovilla). In the pollen of very many plants the outer coat forms one or more regularly arranged folds inwards, in which it very frequently exhibits pore-like, thinner places at one or more points; in hke manner, very many pollen-grains without the folds, have similar pore-like" places, varying from one to a very considerable number, which when large are closed by a pisce of the outer coat serving as a cover. When a pollen-grain comes in contact with water, it powerfully absorbs this, through the endosmose excited by its dense fluid con- tents, swells up and tears in many places, in consequence of the strong expansion its memhianes undergo through the absorption of water. If the pollen-grain opposes the pressure of the absorbed water through the toughness of its membrane, the inner membrane is driven out, in such pollen-grain as have pore-like places in their outer coat, in the form of a papilla, which often extends into a rather long, cyHndrical tube (e. g,, in Dipsacese, Geraniacese, Cu- cubitacese). As this phenomenon occurs in pollen-grains which have been long dried, and in fact very suddenly, it can be attributed only to mechanical expansion dependent on the peculiar structure of the parts referred to, and not to an actual growth. But when firesh, living pollen comes in contact with water wMch contains organic substance in solution, e. g,y with the stigmatic secretion of the fluid of the nectaries of flowers, its inner coat grows out, in one or more places, in the form of a tube, the length 128 ANATOMT AND PHYSIOLOGY OF of wMch, by true growth depending on nutrition, often comes to exceed the diameter of the pollen-grain a hundred times. Ohserv. The graaules of the fovilla have given rise to many false asser- tions ; Ad. Brongaiart, hi particiilarj thought he had discovered that tliey agreed in form and size in each species of plant, and had an independent motion, whence he compared them with the spermatozoa of animals {''Ann. d, /So. nat^ xii. 40., xv. 381). Eob. Brown also {'' A Brief Account of MiGTOscopic Ohserv. on the Particles contained in the Pollen of Plants^' 1828), although he discovered at the very time the molecular motion of the fovilla-granules, was of opinion that a change of form might be perceived in the larger granules (which he called particles). Agamst these state- ments I was compelled to declare most positively (" Ueher d. pollen^' 30), I neither found a definite form and size of the granules in the pollen of any given plant, nor could detect in them movement of any other charac- ter than that of the molecular movement ; to similar results came Fritzsche (" Ueh. d. pollen,'' 24), who shewed that these very grains which had been as- serted by Brongniart and Brown to change their form, were nothing but starch grains, while other seeming granules were drops of oils j the ma- jority of the smaller granules may, however, as in all protoplasm, consist of proteine compounds. These granules are invisible in many fresh pol- lens, since the fluid in which they swim has the same refractive power as the granules, whence such pollen-grains are as transparent as glass lenses; when their fovilla is mixed with water the granules at once become visible. The fovilla seems always to be at rest in the pollen-grain when it comes from the anther, unless Zostera (Fritzsche L c. 5QJ forms an exception. But when the pollen-grain has germinated upon the stigma, the foYilla exhibits a circulation similar to that of the protoplasm of Vallisneria and Chara, flowing downwards in a t3road stream into the pollen-tube, and back upwards on the oppo- site side. Ohserv, This phenomenon was first seen by Amici in Portulaca (" Ann. d. Sc. nat.'' ii. 68), subsequently in other plants, especially in Gourds and in Ilihiscus syriacus {'^ Ann. d. 8c. nat.'' xxi 329). Since it appears that no other observer (except Schleiden, who saw the circulation in pollen- tubes which had been developed in nectar) has been able to see tliis pheno- menon, it may be permitted me to mention how the observation is to be made. In Portulaca it is not difiicult, if a freshly-impregnated stigma is exposed to bright sunshine for a few mmutes, the style then removed from the flower with forceps, and the stigma upon which the pollen tubes are veiy quickly formed, is observed dry, with a power of at least 200 diameters. In the Gourd (for as Amici told me himself, his observations were made on this plant, which in Italian is ^ucca, and not on Yucca as it is stated in all books) a layer must be sliced from a stigma powdered with pollen an hour previously, and this slice pressed moderately between two glass plates, to heighten its transparency. In the development of a filament from the internal coat of the pollen, we meet with a new analogy between the pollen-grain and the spores of Oryptogamous plants, since we have evidently before us a process of germi- THE VEGETABLE CELL. 129 ' nation resembling that we observe in the spore. Bat the pollen-grain does not seem to be capable of a farther deyelopraent, under fayourable external cireumstances^ into a plant like the parent, yet Reisseck and Karsten observed that under certam circamstance&, e. ^., when pollen-grams were enclosed in hollow stems like that of the Dahlia, their inner coat was ca]}able of an abnormal development, and of conversion into lower forms of Fungi. ** The OduU. The Ovule {ovulwm, Elchen), — of late years called by the ad- herents of Schleiden's theory of impregaation the seed-bud (samen- knospe) or gemraule, consists essentially of a parenchymatous papilliform growth from the ovary, of the so- called nucleus (ei-kerne, nucleus ovuli fig. 52, Fig. 52. a), the tercine of Mirbel, in which towards the epoch of impregnation one cell becomes more enlarged, displacing a greater or smaller portion of the parenchyma of the nucleus and forming the emhryo-sac (the quintine of Mirbel). In far tlie greater number of cases the ovule does not stand still at this first stage, in wMcli it consists merely of a naked nucleus, but un- dergoes, before impregnation, a more or less extensive series of changes, which relate partly Transverse section of to the formation of enveloping, membranes, en- Imb^o^^'^rm^rioat closinot the nucleus, and partly to alterations of of the ovuie 'iprmnm); f> V n. ^ ^ 1 jfii I'jy* ."» Outer Coat (,v In the majority of ovules, a second coat (fig. 52, d) is formed in the same way, lower down than the first (fig. 52, e) which it encloses. That part of the ovule where the simple or double coat is connect- ed with the base of the nucleus (fig. 52, /), is named the chalaza, and when beneath this there exists a cylindrical portion, it is called the funiculus (nahelstrang, fig. 52, g), Ohserv, Since the changes of form, which the ovules of most plants un- dergo in the course of their development, exercise no influence upon their impregnation, 1 shall be content to indicate briefly their principal modifi- cations. When the axis of the ovule remains straight, as it is always at first, so that the micropyle is situated at the summit of the ovule, and the chalaza coincides with the hilum, both lying at the extremity of the ovule opposite the micropyle, the ovule is called orthotropous or atropous (gerad- laufig). When the ovule curves over on the end of the funiculus, so that the upper part of the latter comes to lie parallel with one side of the ovule and grows together with it, the ovule is named miatropous (gegenMu- J-ig), In an ovule of this kind the chalaza Hes at the geometrical summit of IT ISO AK ATOMY AND PHYSIOLOGY OF tlie whole, tKe funiculus coherent with the ovule forms a ridge running along one side (the raphe), the hilum (the point of insertion of the funicu- lus) lies beside the mieropyle, at the lower end of the ovule, and the axis of the nucleus is straight. But when the nucleus itself is curved to one side by an unequl growth of its two sides ; so that the micropyle comes to lie beside the clialaza at the base of the ovule, and the highest point of the ovule is formed by the curved side-wall, the ovule is called campylo- tropous (kTwnmlaujig). Although not difficult of investigation, the knowledge of the structure of the ovule advanced very slowly. An excellent foundation was laid by Malpighi; but it was Robert Brown, who first opened the path to further progress, by his desciiption of the ovule of Kingia, The researches of Brongniart and Mirbel, which latter clearly unfolded the mode of ori- gin of the different forms of the ovule from the orthotropous, but gave a very incorrect account of the coats of the ovule, were followed by the ob- servations of Fritzsche, who cleared up the latter point, and the extensive investigations of Schleiden, who, through a large quantity of detailed re- search, earned very great credit by making known the different modifica- tions of the structure, — the varying number of the coats, — the universal occurrence of the embryo-sac, — the origin of this from a cell, ko. Hof- meister (" D. Entsteh. d. Mmhryo der Fhanerog. ") traced back the earliest stages of development of the ovule further than any previous observer, and found (in the Orchidese) that it takes its origin from a single cell of the epidermis of the placenta this cell dividing by a cross section into two cells, one lying above the other, the upper of which, is converted by further subdivision into the cortical layer of the nucleus, and the lower, into the central cellular cord, the uppermost cell of which becomes the embryo-sac. According to the ordruaiy view, the ovule is to be considered as a bud, the axis of which is metamorphosed into the funiculus and nucleus, the leaves into the coats of the ovule. The order in which the coats are de- veloped, might certainly be fairly urged against this opinion ; but I can- not question its correctness, since it is not unfrequent in malformed ovaries, for the ovules to grow out into leafy shoots. "With regard to the physiological import of impregnation, it is perfectly a matter of indifference whether the ovule is regarded as a product of the carpellary leaves, according to the theory advocated by Bobert Brown and Be CandoUe, or it is assumed, with Schleiden, Endlicher, and Unger, and others, that the placenta is always an axial structure. It would lead me too far to relate the reasons for and against these two theories ; each of which is true of a portion of the Vegetable Kingdom, but neither of which, and especially the latter, can be exclusively applied to all plants, without coming into contradiction to the clearest facts. Detailed researches on the structure of the ovule are to be met with, especially in the works of Mirbel ( " Bech. sur la struciure et devehppement de Vovuh tiegUah,'"' Ann, desSc. nat. xvii), Schleiden (^" JJeK die, Bildung de^ Eichens" Act. nat cur, xix. p. L ^^Grundz der wiss, Bota>ni7c'^)^ Hof- mai^ter f'Die Bntstehung des Emlryo der Fhanerog^ and Tulasne (" Ann, dm Sc, nat Zme S^er^ xii). "^^ The Origin of the JEmlryo. The impregnation of the ovule by the pollen is an indispensable condition to the origin of an embryo in it. It is true that the THE VEGETABLE CjELL. 131 ovary may grow up into a fruit, and the ovule into a seed nor- mally formed on the exterior, without this, but the latter is in- capable of germination, because it contains no embryo. In the naked-seeded Phanerogamia (the Cycadese and Coniferse), the pollen falls upon the freely-exposed ovule, and impregnates it immediately; in the rest of the Phanerogamia, in which the ovules are enclosed in an ovary, the impregnation is effected through the medium of the pistU, with the stigma of which the pollen must come in contact. In the majority of plants, the ovary is not perfectly closed above, its cavity being prolonged upward into a very narrow canal, which runs through the substance of the style ; or if the borders of the carpellary leaf where this forms the style, are not blended together, it has the form of a groove running on the inside of the style. The cellular tissue which forms the wall of this canal, is distinguished from the rest of the tissue of the style by softness and transparency, and frequently also by the absence of colour. At the epoch of the perfect development of the pistil, there exudes among its cells (which are usually much elongated, but may also be roundish) a mucilaginous fluid, which so loosens the connection of the cells, that they may be readily separated, ^and through the expansion caused by the excreted fluid, they frequently quite close up the canal of the style. This cellular tissue, which, after Ad. Brongniart, is called the conductiTig tissue, appears at the upper orifice of the canal, where it is frequently enlarged into a large globular or lobulated body, free to the external air, and this constitutes the stigma. The cells forming the stigma are ordi- narily less elongated than those lying in the interior of the style, and are often more firmly blended together. The outermost layer of them does not form a continuous, smooth epidermis, but its cells are usually in the form of papillae of variable length ; and papillae of this kind present themselves along the whole of the canal of the style, upon the surface of the conducting tissue. At the opposite extremity of the canal, the conducting tissue stretches into the cavity of the ovary, and here, in general, runs on its wall to the points of insertion of the ovules, where it appears in very diflerent forms, varying according to the structui'e of the ovary, the number and position of the ovules, &c. ; sometimes covering the many-ovuled placenta as a broad layer ; sometimes running, in the form of a narrow strip, to a single ovule ; sometimes pro- jecting, in a conical shape, into the <^vity of the ovary, and coming into direct contact with the micropyle of an ovule, &jc. The conducting tissue is by no means to be regarded as a special organ, but consists of a modification of the tissue of the carpellary leaf, occurring at particular parts,— usually of its upper surface, where this forms the canal of the style. In other cases, however, this modification of the tissue may go out through the substance of the carpellary leaf to its posterior surface^ as in the Asclepiadeje, 132 ANATOMY AND PHYSIOLOGY OF in which this forms but a very small part of the colossal style, or in Lomatogonium, where the coherent borders of the carpellary leaves consist of stigmatic substance along the whole of the ovary. The pistil is incapable of fertilization, until after the secretion of the above-mentioned viscid fluid upon the stigma, for though the pollen-grains indeed adhere to the stigma from being more or less glutinous, they cannot be any farther affected. But as soon as this secretion has appeared, the germination of the pollen- grains commences, often in a few minutes, in any case in a few hours. The inner coat breaks through the outer in the form of a cylindrical tube, which applies itself to the stigmatic papillae (sometimes, as in Matthiola annua, penetrates into them), grows downwards among them, and penetrates between the cells of the conducting tissue. Ordinarily only one tube is emitted from each grain, but in those grains which possess several pore4ike points on their outer coat, and in which the portion of the inner coat situated beneath those places always becomes developed into a tube, one grain not unfrequently produces several tubes, the number having been seen by Amici to amount to 20 — 30, The pollen-tubes make their way, by continuous growth at their ends, through the conducting tissue of the style into the ovary, attaining, in long- styled plants, like Gaotus grandifiorus, for instance, a length which may exceed the diameter of the pollen-grain several thousand times. This considerable length alone, but still more the circumstance that the wall of the pollen-tube is often exceedingly thin in proportion to its cavity, shews that its formation does not depend upon mechanical extension of the pollen-membrane, but on a growth, the requisite nutriment for which is drawn from the viscidfluid poured out among the cells of the conducting tissue. The rate at which the growth takes place varies very much in different plants, and is not subject to any universal rule. The first result of it is an attachment of the pollen-grain to the stigma, so that it can no longer be readily wiped off* the latter. According to Gartner, this often takes place in even half a minute, while, in other cases, many hours may elapse (in Mirahilis and the Mal- vacece, as many as 24 — 36). The growth of the pollen4ube down the style likewise occupies very varied periods in different plants. In many plants, several weeks pass before the pollen-tubes have passed through a stjde only a few lines long, while in others, even when the style is very long, a few hours suffice (6.g., in Cactus grandifiorus and Golchicum). After the pollen-tubes have penetrated the stigma, the secretion of the latter ceases, and its tissue begins to die away, while the lower part of the pollen - tube is still in a growing condition. The fovilla passes down- wards in proportion as the tubes are elongated, so that the pollen- grains collapse on the stigma soon after their application upon it. The pollen-tubes being so long, the fovilla must certainly become more and more considerably diluted by the absorbed fluid, jet it THE YEGETABLE CELL. 1S3 seems always to become more or less granular and opake. The pollen-tubes are distinguishable from the cells of the conducting tissue, partly by their opake contents, and partly by their smaller diameter (which is often very small, e, g., in Orchis Morio about 1-1 80th of a millim, in Digitalis purpurea l'-]66th, in Oheir- anthus Cheiri l~280th, in Gapsella Bibrsa-pastoris 1-832). Arrived in the ovaxy, the pollen-tubes, when not immediately led to the mouths of the ovules by special arrangements of the conducting tissue, creep in a mostly very serpentine course along the placenta, among the ovules, and finally penetrate singly, or several together^ into the micropyle canals of the ovules. Ohserv. A considerable time elapsed from Amici's first observation on the emission of the pollen-tubes upon the stigma of Fortulaca (1823), before their further path to the ovule was detected ; for though Brong- niart (1826) demonstrated, by numerous obfeervations, that the pollen-tubes penetrated the conducting tissue, he thought he found that theb lower endb burst, and that their fovilla was conveyed to the ovules by the con- ducting tissue. Amici (1830, ^^Ann. cl Sc. nat'' xxi, 329) discovered the perfect course to the ovule, but even in 1832, Eobert Brown was still in doubt whether the tubes penetrating the ovules of the Orchidese were pollen- tubes, or, more probably, tubes termed in the style, and to which he applied the name of mibcous tubes, a doubt which was com|>letely settled by Amici's researches, as was also the opinion advanced by many later observers, that this phenomenon does not occur in all the Phanero- gamia : — shewn to be totally mistaken, by the extensive researches of Sclileiden, Hofmeister, (fee. It is one of the most puzzling phenomena existing, that the ends of the pollen-tubes reach the micropyles of the ovules, the admibsion to which is not always very simple ; since this rencontre seems to be lefl to pure acci- dent, it might be conjectm^ed that for this purpose a very large number of pollen-tubes were necessary. Yet such is not the case. It is tx-ue that in the majority of plants, the number of pollen-tubes which are deve- loped upon the stigma is very considerable, and we not unfrequently see whole bundles of them penetrate the ovary, which is readily accounted for by the vast number of pollen-grains found in the flowei^s, a tolerable proportion of "which generally reach the stigma. Thus Kdlreuter found 4863 pollen-grains in the flower Hibiscus Trionum^ and according to Amici's esthnate the pollen-grains of an anther of Orchis Morio can fur- nish 120,000 pollen-tubes. But the number of poUen-gi'-ains necessary for impregnation is by no means large. For example, in Kolreuter's experiments on Hibiscus Trionum, 50 — 60 pollen-grains sufficed to impreg- nate all the ovules in the ovary (over 30) ; when fewer pollen-grains were placed upon the stigma the ovules were not all impregnated, for in- stance, by 25 pollen-grains only 10 — 16 ovules. In Mi/rahiMs Jah/pa and hngiflora one, or at most three, sufficed to impregnate the ovule. It is not necessary to the success of an impregnation that the pollen should pass immediately from the anther to the stigma, for it seems to remain capable of fertilizing for some days in all plants, while in some it retains its power even for a year. Thus Kdlreuter found that the pollen of Hibiscus Tfiovhum kept fresh three days, that of Ckei/ramtlms Ghm/r% fom^teen days ; the pollen of Fhmnix dactylifora is said to be capable of 134 ANATOMY AND PHYSIOLOGY OF being preserved for a year in the East ; and the name time ha^ been asserted for Cannabis, Zea, and Cmmllia. (See Gartner " BefrucMung der Gewachbe,'' 1, 146.) In order to explain the course of the processes which go on in the interior of the ovule, it will be necessary for me to return to its structure. Towards the epoch of impregnation, the embryo- sac has mostly become greatly enlarged in proportion to the other parts. In many plants it is still enclosed in the interior of the nucleus, so that its upper end, directed towards the micropyle, is still covered by one or more layers of parenchymatous cells be- longing to the nucleus. In other plants (for example in the Or- chidese and Syngene&ia), the embryo-sac (pi. 1, fig. 12, s; 13, s) has by this time wlioUy displaced the entire nucleus, or at least the upper part of it (in the Leguminosse also the inner coat of the ovule), and in certain cases, in particular in Santalum, has be- come so much elongated that it projects freely out of the micro- pyle. The pollen-tube which has penetrated into the micropyle (pi. 1, fig. 14, _p : 1 5, 2>.) in its further elongation, thus comes either immediately in contact with the apex of the embryo-sac, or with the layer of cells coveiing it ; in the latter case it penetrates between these cells, and in this way likewise reaches the embryo-sac. In the latter there is always a more or less abundant quantity of protoplasm. In the later period, just before the pollen-tube reaches the embryo-sac, a portion of the protoplasm becomes at- tracted into the upper end, next the micropyle. In this proto- * plasm nuclei appear, usually to the number of three (pi. 1, fig. 12), and give lise to the formation of as many cells (pi 1, fig. 13, b; 14), which more or less completely fill up the npper part of the cavity of the embryo-sac, and are termed the germinal vesicles {embryo- blaschen). The triple number, although usual, is not universal, for in many plants (e. g., Agrostemma Gfithago, according to Hof- meister) only one germinal vesicle is formed, while in other cases, as in Funckia coerulea, a larger number present themselves. One of them also, as Hofmeister observed in Ganna, may displace the rest before impregnation through its predominating enlargement. "With these cells necessary for the origin of the embryo, a variable number of other cells are also formed in other parts of the embryo- sac (pi. 1, fig. 4, /), chiefly in the end turned away fi:om the mi- cropyle, more rarely in the central region. But this cell-formation is neither an universal phenomenon, nor does it stand m relation to the impregnation. When the pollen-tube has reached the upper part of the embryo- sac, its growth is either immediately arrested, or it becomes elon- gated a very little more, so that its obtuse, somewhat inflated end usually penetrates laterally between the embryo-sac and the sur- rounding cellular layer (pi. 1, fig. 14^ 15), or, in rare cases (Ifareis- sus poeticus, according to Hofineister ; Digitalis purpurea, and Campanula Medium, according to Tulasne), introverts the mem- THE VEaETABLE CELL. 135 brane of the embryo-sac for a short space. In extremely rare cases (in Ganna^ according to Hofineister), the pollen-tube breaks through the membrane of the embryo-sac, and thns comes imme- diately in contact with the ger}ninal vesicles. In the great jnajority of cases, however, as already observed, the pollen-tube is separated from the germinal vesicles by the membrane of the embryo-sac, and frequently even, the point at which the end of the pollen-tube is in contact with the embryo-sac, does not correspond exactly to the point at which a germinal vesicle lies in the inside of the em- bryo-sac (pi. 1, fig. 15). Therefore the only way in which a mate- rial effect can be produced by the pollen-tube upon the germinal vesicle, is by the fluid part of the fovilla transuding through the membranes of the pollen-tube,' the embryo-sac, and the germinal vesicle. It cannot be demonstrated that such a transudation does take place, but it is in the highest degree probable, since it is in- comprehensible how the impregnation of the germinal vesicle could take place without it. The pollen-tube begins to decay more or less rapidly after it has reached the embryo-sac. Its growth is arrested, as before noticed, and the fovilla contained in it undergoes a visible change in its characters, acquiring a granular, half coagulated aspect ; the pollen-tube itself is by this time evidently dead, and disappears sooner or later (sometimes, however, not until the seed is ripe), apparently through absorption. Shortly after the meeting of the pollen-tube with the embryo- sac, but only when this has occurred, the farther development of the germinal vesicle begins, this exhibiting a rapid growth, and usually displacing the two other germinal vesicles which ordi- narily accompany it (pi. 1, fig. 15); it is only in rare cases that two or more of these vesicles simultaneously undergo enlargement. The form which the growing germinal vesicle assumes is very un- like in different plants ; in many it grows but moderately in the longitudinal direction, and thus becomes ovate; in others, particularly in the Scrophularinese and Cruciferse, it grows into a long cylinder, winch frequently does not much exceed the pollen- tube in diameter, and exhibits a clavate expansion at its lower extremity. During this enlargement, the protoplasm, which ori- ginally filled up the germinal vesicle pretty uniformly, becomes principally collected at the lower end, after which cell-formation by division commences (pL 1, fig. 15, 16). In this conversion of the germinal vesicle into a cellular body, to which Hofmeister applies the name o{ pro-embryo (vorkeim), abundance of modifica- tions present themselves in different plants. In all cases the vesicle first divides by a transverse wall into two cells, one above the other (pi. 1, fig. 16, a, 6.) ; the lower of these may at once be- come converted into a parenchymatous body (the embryo) by suc- cessive subdivisions, as occurs in Monotropa, or, as is ordinariljr the case, the formation of the embryo does not commence until 136 ANATOMY AND PHYSIOLOGY OF the pro-em"bryo has been changed into a compound cellnlai* body by successive subdivi&ions. In this process there may be forma- tion merely of cross-walls, so as to change the pro-embryo into a conferYoid, jointed (pi. I, fig. 17, a; 18, a) fiequently elongated row of cells lying one above another (for example, in the Scro- phnJarinese and Cruciferse), or the filamentous pro-embryo may pretty early pass into a mass of cellular tissue by longitudinal division of its cells (for instance, in Statice, TropcBolum^ Zea, Fri- tillaria^ &c.). Whichever takes place, the terminal cell of the whole structure is sooner or later metamorphosed, by preponder- ating giowth and cell-division in diflerent directions, into a cel- lular structure, at first of globular form (pi. 1, fig. 17, &; 1S,b), which, the more fully it becomes developed, the more marked contrast does it present to the other part of the pro-embryo turned towards the micropyle end (called the suspensor, Trager^ or Aufhang&faden), The ulterior development shews that this mass of cells foimed at the end of the pro- embryo is in the rudi- ment of the embryo. It may persist, in plants with the so-called " homogeneous embryo^' (e. g,, in the Orchidese and in Monotroi^a)^ in the form of a globular or elliptical body, composed of a variable number of cells (pi. 1, fig. 1 8) ; but usually the cotyledons shoot out at the end turned away from the suspensor, a little below the actual extremity (in the Monocotyledons in the form of a sheath- ing leaf, in the Dicotyledons in the form of two opposite leaves,) and after this the apex is developed into the terminal bud (^plu- muUf federchen). In this way the embryo is always suspended in an inverted direction, with the point of its stem downwards, in the embryo- sac. Its radical extremity, as is evident from the mode of origin of the embryo, is not free, but blended with the cells of the pro- embryo ; frequently it does not at once become clearly distin- guishable from the cells of the pro-embryo, but the line of de- marcation becomes continually more definite with the advancing development, since the cells of the embryo are always densely filled with organic matters, while the cells of the suspensor -usually contain only a little opake sap, and are thus far more transparent than those of the embryo, fi:om which they are also fi^equently distinguishable by much greater si^e. The further the develop- ment of the embr;^ o progresses, the more, in most cases, does vege- tation cease in the cells of the suspensor, so that, if even, as in the Orchidese, it still exil)its a considerable growth during the deve- lopment of the embryo, and exists when the seed is ripe, it at all events forms but a dead, readily detachable appendage of the radicle, upon the embryo of the ripe seed. The origin of the embryo, which is formed out of a cell of the pro-embryo, and liot free in the cavity of the embryo-sac, bears great resemblance to the formation of a bud, and especially to the for- mation of the stem-producing buds developed on the pro-embryo of THE VEGETABLE CELL. 1S7 the Oryptogamia ; yet there exists an important distinction fi-om t!ie formation of buds, in the fact that the lower end, connected with the suspensor, becomes detached from this, and is capable of further development, in consequence of which the primary axis of the embryo can become elongated downwards, in germination, as a tap-root, which is not the case in any buds, or in the young stems of the Oryptogamia,* the axis of which is only capable of prolongation upwards » Ohserv. L Schleiden's theory of the origin of the embryo ('' Minige Blicke aufdie EntwickelungsgescM elite des veget. Organismus^^ Wiegmann's ^^AtcIivo'' 1837, 1, 289 — " Ueber die Bildmig des Bichens und BntsteJiung des Bmhryo'' Act. acad. nat Otir. v. xix., p. 1.) is completely opposed to the foregoing description of this procebS, since, according to him, the embryo is not formed in the cavity of the embryo-sac, but in the lower end of the pollen-tube, which mtroverts the wall of the embryo-sac, and penetrates more or less deeply into the depi-ession thus formed. If this theory were true, the germinal vesicle would not he an hidependent pro- duct of the ovule, but of the clavate, expanded extremity of the polien-tube, and the suspen&or would be the remainder of the latter, ranning into the mtroverted portion of the embryo-sac. In the whole province of Vege- table Physiology, seldom has a theory excited so much curiosity as this theory of impregnation. ISTo conviction was moi*e firmly established than that the pollen was the impregnating organ, hence the wonder that it should be exactly the reverse. The confusion was great, for the theory emanated from a man who shewed by his numerous and excellent re- searches on the ovule, pubHshed at the same time, that he possessed an acquaintance with his subject, such as few others had, and who in every word expressed the conviction that the matter did occur as he asserted, and that a mistake was out of the question. And others were not want- ing to make known confirmatory observations (Wydler, *' BihliotK Uni- mrs" 1838, Oct.; Geleznoff, " Bot. Zeitung,'' 1843, 841), or to support the new doctrine on theoretical grounds, and teach it as a settled truth (Endhcher and linger, " Grundz der BotanW). It is true that the old notion had its defenders, but these maintamed the fight a long time with little success. Some who did not know how to use the microscope, thought, nevertheless, that an opinion might be arrived at here, in which the thing depended wholly and solely upon a fact to be determined by the micro- scope, from other grounds, but such was utterly without value by itself ; others, Meyen in particular (^^ Physiologie^' in), certainly had recourse to the microscope, but were content with superficial observations, and thus were not very fortunate in their intended refutation of the new theory, for observations, in some of which not even the penetration of the pollen- tube into the ovule, or the embryo-sac were seen, were not calculated to drive an opponent like Schleiden out of the field, and the latter could justly interpret some among such discordant observations as Meyen's in his own favour. It was Amici again who now for the second time came forward with an observation marking an epoch in the theory of impregna- '* An error ; the axis of the Ferns, &c., originates from a free embryonal vesicle, and has an abortive descending axis, like the Monocotyledona — -A.. jjL. 128 ANATOMY AND PHYSIOLOGY OF tion, and, by lais researches on tlie impregnation of the Orchidese (" Sulla fecundazlone delle Orchidee^' — Giorn. Bot. Italian. Anno 2), made an end of the new theory at one blow. Amici's treatise was soon followed by a confirmation of what he had seen by mybelf (" JBot Zeifung'' 1847, 465), and others ; and these were quickly succeeded by the extensive researches of Hofmeister (" Die Entstehung d Embryo d. EhaneTogammC^ and of Tulasne (" Ann. d. Sc. nat 3 Ser. xii), which contained a full confirmation of the results obtained in the Orchidese, and demonstrated that the im- pregnative process is the same in its essential circumstances throughout a long series of Phanerogamia, so that this subject may be considered as quite settled in its principal features. Ohs. 2. The so-called naked-seeded Dicotyledons (the Cycadese and Coniferse) present some very important differences from all other Phane- gamia, in reference to the production of their embryo ; the circumstances are unfortunately not all cleared up by the foregoing researches. The differences depend, not so much upon the fact, that the pollen-grains fall immediately upon the naked ovules in these plants, for nothing is essen- tially altered by this, since the pollen-grains here germinate on the point of the nucleus in the same way as in other plants, and are thus spared the circuitous route which the pollen-tubes have to make through the con- ducting tissue of the pistil. The distinctions lie in a great compHcation of the structure of the ovule, ajid in the manifold deviations in the struc- ture of the embryo. In the Coniferse, the nucleus is in great part displaced by the enlarge- ment of the embryo-sac ; the latter becomes filled with cellular tissue, out of which from three to six cells, arranged in a circle near the upper end, become more considerably enlarged than the rest, and these consti- tute what are caUed, by Robert Brown, the carpuscula^ — ^by Mirbel and Spach, the secondary emhryo-sacs, — and also become filled up with cellular tissue. The pollen-graixis germinate on the point of the nucleus, and send down their tubes through the upper part of it j and the slowness with which this process takes place in many species is remarkable, for in Larix europcea^ according to G61eznoff, the pollen-tubes do not emerge from the granules till after thirty-five days ; and in Pinus syhestris, Pineau states that fall a year passes before they grow down through the nucleus to the embryo-sac, whereby evidently the impregnation is also postponed for this long period. When the poUen-tubes have arrived at the embryo-sac, they break through it, and through the cellular tissue lying between its mem- branes and the secondary embryo-sacs. The observations on their subse- quent course are discordant. Pineau believed he had discovered that the ends burst, and poured out the fovilla into the secondary embryo-sacs. According to G616znoff, the pollen-tubes would break through an inner membrane immediately enclosing the fovilla, and grow into the secondary embryo-sac. In like manner, there is an obscurity as to the origin of the embryo. Apparently there originates in the secondary embryo-sacs, from the cells already contained in them, a pro-embryo of most peculiar form : ia Finus, the upper part of it is composed of a rosette of four to five cells, to which an equal number are applied below, these extend them- selves into a long filament, which again bears four cells at its extremity constituting the rudiment of the embryo. As the intermediate cells grow down in the filamentous form, they break through the lower end of THE VEGETABLE CELL. 139 tlio secondary embiyo-sac&, grow oaward in the cellular tissue Ijing in a cavity of the primary embryo-sac, and push the embryo out of the secon- dary embryo-sac. In this way are formed as many embryos as there are secondary embryo-sacs ; but the four or five cells forming the thread-like suspensor may separate from each other, and every one form a special embryo. The embryo itself, moreover, exhibits a peculiar growth, for while its cotyledonary end is composed of a connected, well-defined mass of cells, its radical extremity is formed of a loose mass of cellular tissue, which grows back on the suspensor, its cells only becoming more com- pactly conjoined at a later period. Finally, in Thmja^ a whole mass of such suspensors are formed, which terminate in an embryo below, side by side, in one embryo-sac. The numerous embryos originating in one ovule seem all to be equally capable of living, and are developed up to a certain point, bat then, from some unknown cause, all die away except one. (Robert Brown, " On the Flurality and Development of JEnihryos in tJie Seeds of tlie GonifercB',' — Ann. Wat Hist, 1. 8er. xiii. 368 ; Mirbel and Spach, '' JVotes sur rEjiihryogenie dw Finns Zarido" &)o./' Ann. des Sc. nat^ 2 S6r. XX. 257 ; Pineau, " Sur la Formation de VEmbryon chez les Goni- fere^l' — Ann. des Sc. nat 3 Ser. xi. 83 ; G^leznojBT, "/Swr rUmhryogenie du Meleze, Bulletin^ de la Societe deNatwral. de Moscou^' xxii, '^ Ann. des So. naf" 3 S"er. xiv.)^ Observ. 3. If Schleiden's theory of impregnation had proved true, it would have farnished incontestibie proof that no embryo can originate in the ovule without application of pollen to the stigma. With the con- firmation of the earher view of the import of the pollen-grain, the doubt again arises whether the geminal vesicle is not in isolated cases capable of development into an embryo without impregnation. Improbable as such an exception seems, when we look at the thousands of experiments which declare the necessity of impregnation, the absolute impossibility of it can the less be proved that undoubted cases of the possibility have been shewn in the Animal Kingdom. The greater the accuracy in the observa- tions, indeed, the more clear it became that the cases in which it was supposed that the development of fertile seeds without impregnation had been obseiwed, in the hemp, spinach,