Cornell Uni ity Library QK 731.887” wi CTT 3 1924 000 663 033 aBE ‘ce @F poGgTOR oriéniledaders. 1914. oy AAG GROWTH STUDIES. IN FOREST TREES bh PINUS. RIGIDA MILL SOWIE PLATES xxiv" ‘aND XKvys HARRY: P. BROWN Brat “t ‘ } Reprinted f for-private circulation from, © 4 tae a GazErre, Vol. Liv, ‘No. S, November. 1gr2 GROWTH STUDIES IN FOREST TREES 1. PINUS RIGIDA MILL (WITH PLATES XXIV AND XXV) HARRY P. BROWN . Reprinted for private circulation from | Tse Botanicat Gazette, Vol. LIV, No. 5, November 1912 GROWTH STUDIES IN FOREST TREES 1. PINUS RIGIDA MILL Harry P. Brown (WITH PLATES XXIV AND XXV) The phenomenon of tree growth has long been a subject of investigation. Sacus, Huco pE Vries, NORDLINGER, Mer, the Hartics, WIELER, BUSGEN, VON Mod, and a host of others have worked on problems concerned with it, and many papers presenting the results of investigations are to be found in the literature of the last half-century. As might be expected, the question has resolved itself into a number of minor topics, each with its coterie of followers. Some have placed particular stress on spring and summer wood forma- tion; others have studied growth as related to external factors or to inheritance. Various instruments have been devised to measure tree growth, and one author (REUSS 12) goes so far as to assert that thunderstorms cause a growth stimulus in trees. Investiga- tions dealing with every phase of the subject are described in exhaustive detail, and yet with rare exception there is a maze of conflicting opinion sufficient to confuse even the careful reader. The present studies were undertaken with a twofold purpose, namely, to clear up disputed points regarding annual ring forma- tion in trees and to formulate laws of tree growth. Investigations were carried on upon various forest trees with this idea in view. The results of those on Pinus rigida are embodied in this paper. Secondary thickening in trees arises as a general rule from a cambium which lives from year to year. This annually passes through certain active and certain dormant periods. The latter assertion, however, is to be taken in its broadest sense. In many tropical woods the interruption to growth can be detected only with a microscope, while in others it is totally lacking; the wood appears * Contribution from the Department of Botany, Cornell University. No. 148. Botanical Gazette, vol. 54] [386 1912] BROWN—PINUS RIGIDA 387 as a homogeneous mass. The formation of this cambial layer takes place the first year, and is brought about by the linking together, so to speak, of the fascicular cambium of the primary bundles by the formation of interfascicular cambial zones, the result being a cylinder of merismatic tissue capable of division. There are, in addition to this, however, certain other growth phenomena. In the cortex of many trees, either near or remotely distant from the primary cambium, secondary cambial zones arise, whose function it is to form cork, the so-called cork cambiums. They are not united in a ring, as is the primary cambium, but extend for com- paratively short distances in a peripheral direction” Again, as met with in the Cycadales and Gnetales (CouLTER and CHAMBERLAIN 4), successive bundle-forming cambiums sometimes arise toward the periphery of the stem, and in such cases the life of the primary cambium is generally very short. Further, among dicotyledons there are a number of modifications of secondary thickening, par- ticularly in underground parts. In the present’ studies, however, it is the intention to confine investigation to growth as it normally occurs in trees, that is, to the activities of a cambium which has certain active and certain dormant periods. A number of specimens of Pinus rigida in the Cornell pinery as: well as others in the wild state were used. Those in the nursery consisted of a number of individuals standing in a row which ran approximately east and west. The land sloped gently to the south- west and drainage conditions appeared to be good. The individual trees were about 22 years of age and seemed to be in a thriving condition. The height varied from 6 to 7 m., depending on the vigor of the individual, and the average diameter at breast height was 12cm. In 1909, when investigation began, the branches extended to within 1.2m. of the ground. However, during the year above mentioned, the trees were pruned to a height of 1.9 m. above the ground. Experiments were carried on with six indi- viduals of this series, which were numbered I-VI. The trees in the wild state had better be described separately, since each was of different age and external factors varied with the individual. For the sake of clearness they were designated as 2 Exceptions to this rule occur, resulting in the so-called “‘ring-barked” trees. 388 BOTANICAL GAZETTE [NOVEMBER A, B,andC. These specimens were growing in a strip of woodland about one mile north of the university campus. Conditions of soil and light appeared to be good in every case, that is, to all appearances the trees were not retarded. Tree A was a magnificent specimen about 25 m. high; in other words, it had practically reached its maximum size. The trunk was slightly shaded to a height of 4.5 m. by an undergrowth com- posed of white pine. There were no branches above for 18 m. until the crown began. The latter was but fairly developed, being about what one might expect under forest conditions. At breast height, the caliper measure was 50cm. A conservative estimate of the age would be roo years. Tree B was a younger individual. Its height was approximately 20m., and crown development had progressed but poorly. At breast height the caliper measure was 26 cm. The base was entirely free of undergrowth, and light conditions were better inas- much as there were no close neighbors. Tree B then differed from tree A in (a) age, (6) light conditions, (c) crown development, (d) height, and (e) diameter. Tree C was about the age of those in the nursery, namely 20~25 years, and rose to a height of 7m. Branches were borne practically to the ground. The caliper measure was 11 cm. Illumination was better on the south side, due to the close proximity of a road, while on the north the underbrush encroached slightly. , Methods Investigations began in the spring of 1909, and the last cutting that year was made on July 6. Alternate cuttings were taken from two different individuals at intervals about a week apart, so that two weeks elapsed between incisions on any one-tree. These were made in the following manner. Beginning from the base of the apical shoot, portions of the cortex and wood to a depth of at least one annual ring were removed at intervals of about 50cm. Twelve cuttings were made in this manner with the aid of a sharp pocket- knife, care being taken not to rupture the cambium. Each cutting was placed in a separate vial, properly labeled with the date, num- Tg12] BROWN—PINUS RIGIDA 389 ber of cutting, and tree, and kept separate from the others in all the successive processes of fixing and imbedding. The following year (1910) cuttings were again resumed on the same trees, as well-as on four more in the same row. The manner of procedure was identical with that above described except (a) every other cutting was omitted and.(d) this season the first cutting was made February 21, the second April 2, and thereafter until the third of May. The object was to check up the results of the previous season and to make new observations. Two cuttings were also made on trees A, B, and C on April 27, one on the north side and one on the south. For purposes of comparison, one root cutting was taken from tree III on the same date. Microscopical characters of the wood As is characteristic of the Coniferae, the secondary wood of Pinus rigida is entirely devoid of vessels. It consists almost entirely of tracheids with bordered pits on their radial walls. In cross-section these appear regularly arranged in radial rows, which occasionally divide as they proceed toward the cambium. In longitudinal section they present the normal tracheid form, that is, a rectangular prism with sloping ends. The annual rings are sharply differentiated. Proceeding from the pith outward in radial direction are numerous pith rays; secondary rays arise in response to necessity; both are of the usual coniferous type.. The histological characters of coniferous wood, however, have been described in detail by PENHALLOw (11), and the reader is referred to his excellent work for further detail. The structure of the secondary thickening in the roots is quite closely related to that of the stem. However, there are one or. two differences. The demarcation between the different rings is not so sharp. This results because the wood of the root is less dense than that of the stem. The tracheids possess wider lumina and there is less summer wood produced. In radial section the bordered pits on the walls are often biseriate, a condition which is never met with in the wood of the aerial portion. 390 BOTANICAL GAZETTE [NOVEMBER Microscopical characters of cambium and cortex in winter condition CROSS-SECTION The radial rows of tracheids in the xylem continue directly out into the cortex (fig. 9) through the cambial zone. For a time this radial arrangement is maintained, but sooner or later it becomes irregular, due to certain changes which take place. The cambial zone in cross-section appears as a number of layers of cells with comparatively thin walls. It is impossible to pick out the initial layer. Exterior to this are the sieve tubes. These have wider lumina than the cells of the cambial zone, and the walls are thick- ened as much as or more than those in the summer wood section of the xylem. However, they are not lignified as are the latter. Companion cells are wholly lacking. The rows of bast parenchyma are very prominent. One row with a few scattered individuals is formed each year (STRASBURGER 13), so that the thickened layers of sieve tubes are separated by thin bands of bast parenchyma. In the outer cortex the bast parenchyma cells become gorged with starch and greatly enlarged. As a result the older sieve areas are stretched tangentially and are seen as thin bands separating the larger cells. Pith rays appear as straight lines running out into the cortex, but as they proceed radially into the cortex they soon become more or less irregular and curved. There are no crystalloge- nous cells such as are described by STRASBURGER in Pinus silvestris. Exterior to the cortex proper there is a series of corky layers which have arisen from living cells in the outer cortex, the so-called cork cambiums. Their structure is of the general type described by STRASBURGER (13). RADIAL SECTION In radial section the cambial cells appear as prisms with sloping ends. The size varies slightly with the age. The sieve tubes have the general shape of the cambium cells from which they originate. Their radial walls are equipped with sieve plates, and these have the same location as the bordered pits on the walls of the tracheids. In radial section likewise we see to best advantage the bast paren- chyma. This consists of rows of barrel-shaped cells arranged one 1912] BROWN—PINUS RIGIDA 301 above the other. There is also a change in the pith rays. The ray tracheids have given rise to ray cells, so that the pith rays con- sist exclusively of the latter. These as well as the bast parenchyma cells contain abundant starch. TANGENTIAL SECTION In order to study cambium and cortex in tangential section, a series of mounts is necessary. The same general characters are observable, but in addition it is evident that there is an entire absence of sieve plates on the tangential walls of the sieve tubes. The callus thickenings of those on the radial walls, however, are particularly noticeable with proper staining (methy] blue). Cambial awakening In taking up the study of xylem formation as it normally occurs in trees, one naturally begins the study before cambial activity begins. Cuttings taken at different heights from tree III on February 21, 1910, all showed in cross-section the general outline of the completed ring. Growth was not manifest in any of the sections. Each ring presented well marked areas of early and late wood. The latter in Pinus rigida is sharply differentiated, owing to its greatly thickened walls. The above statement does not hold true, however, for the wood of the first two or three years at any point in the trunk. Here there is no sharp demarcation between early and late wood. This condition is probably brought about by the fact that the main axis was elongating rapidly at this point when the ring was formed, or else, as these investigations tend to show, growth is slow in beginning in the apical shoot but progresses very fast when once started, so rapidly in fact that there is not sufficient time for the walls to thicken appreciably. In either alternative, there is a gradual thickening in the walls of the late wood of successive rings as the apical shoot progresses aloft. The next set of cuttings were taken on April 4, 1910, from tree III. The cambium was still in the resting condition. Figs. 1-3 and 7-9 show the changes which occurred (figs. 1-3) between April 4 and April 15. In fig. 3 growth is more advanced than in either figs. 1 or 2. The latter are both in the resting condition. So far 392 BOTANICAL GAZETTE [NOVEMBER as can be detected there is no evidence of tracheal formation. Figs. 7-9 are from cuttings made on the same individual at this time, but each successively nearer the ground. In the first two growth is in evidence, while in the last the cambium is still in the resting condition. It is evident from the photographs that in the spring of 1910 growth made itself manifest in tree ITI as early as April 15. Cuttings taken from trees IV and V at the same date likewise showed evidence of cambial activity. While there was no satisfactory evidence obtained the previous year as regards cambial awakening, since observations were begun too late, sections from tree II on May 13, 1910, showed growth in such an advanced state that cambial activity must have begun fully as early the previous year. As regards cambial awakening in trees A, B, and C, no lengthy observations were carried on; but two cuttings per tree were made on April 27, one on the north side and one on the south. At this date trees B and C already showed evidences of growth at breast height in both cuttings. In tree A the cambium was still in the resting condition. However, tree A was older and taller than the other individuals, and it is very evident that growth must have already begun in the higher parts. The observations described above are in accord with those of other investigators. BUscEN (3) gives the time in general for cambial awakening for middle Germany as between the last half of April and the first half of May. R. Hartic (7) has observed that evidences of growth arg manifest in young (10 years) specimens of Pinus silvestris as early as April 20, while its appearance at the base of the older trees depended very much on external factors, such as thickness of stand, soil conditions, ground cover, etc. _Bucxuourt (2), by means of bark measure, gives the date of growth inception in larch and white pine as the last week in April. How- ever, as his computations were made at the base of the trees, probably growth began aloft earlier. That growth was not evi- denced at the base of tree A was due, according to the researches of R. Harrie (7), to at least three causes, namely (a) long trunk, (6) age, and (c) shaded base. While the present investigations do not afford conclusive evidence, inasmuch as they covered but a 1912] BROWN—PINUS RIGIDA 393 period of two years, it would appear that in the vicinity of Ithaca growth began in Pinus rigida at about the same time each spring. To determine this point definitely, however, observations must needs be carried on for a period of years. That growth made itself evident in 1910, however, as early as April 15 is readily apparent from the photographs. Place of cambial awakening The question of origin of growth is still in dispute. T. Hartic (8) claimed that it made itself manifest in the youngest branches first and extended slowly downward. N6ORDLINGER (Forest Botany, 1874) makes the same assertion. R. Haptic (7) appears to accept his father’s statement if we are to judge from the following quota- tion: “Am oberirdischen Stamme beginnt der Zuwachs zuerst in den jiingsten Trieben,” etc. These three investigators, therefore, were unanimous in the opinion that the awakening of growth is earlier at the top of a tree than below. , MER (10) disputes this general assertion. According to his researches, the procedure of awakening was sensibly different in older trees. While in 25-year-old oaks, beeches, and firs, growth was first manifest in the youngest branches, in the older trees it was in evidence at the same time at the bases of the branches and even in the trunk where the roots began. From these points growth gradually extended to the intermediate regions. Figs. 4-6 correspond respectively to those of the preceding numbers, except that a period of 19 days intervened. Comparing those of different date, we see that growth is more in evidence in every case where the cutting was taken at the later date. In figs. x and 2 we have apparently the resting condition, while figs. 4 and 5 exhibit signs of growth, the latter being more in evidence in fig. 5. Comparing figs. 3 and 6, it follows that there is a considerable advance in growth. In the former, at the outside, only two half- formed tracheids are to be seen, while in the latter three or four rows are present and these are of larger size. Comparing figs. 1-6 as a whole, it is evident that during a period of 19 days there was an awakening of cambial activity in the apical portion, first manifest in fig. 3 on Aprilrs5. Growth first appeared in the crown of tree III 394 BOTANICAL GAZETTE [NOVEMBER some distance below the apical shoot, but in a period covering 19 days gradually spread upward and was in progress in the apical shoot on May 4, 1910. Cuttings of May 4 corresponding te figs. 7-9 were not photo- graphed. Examination revealed the fact, however, that growth was in progress throughout the basal portion of the trunk on that date, and had progressed to a greater extent than was evidenced on April 15. From the above investigations it follows that growth was in progress throughout the main axis of the tree on May 4, while 19 days previous it was not in evidence in either the apical portion or the base. If R. Harrie is right in his assertion that growth is first manifest in the branches, Pinus rigida is surely an exception to the rule. Mer’s investigations on young trees are in accord with Hartic’s, so here likewise growth in Pinus rigida appears to pre- sent an anomaly. That Harrie is right in his assertion that cam- bial activity proceeds from the base of the crown downward, investigations on trees A, B, and C seem to give convincing evidence. Cambial activity was already in progress on both sides of the base in trees B and C on April 27, while both cuttings in tree A on that date appeared to be in the resting condition. This is explained in that the trunk of tree B was better illuminated below than that of tree A, while tree C was but 25 years old. But at this date growth must have been in evidence in the upper portions of tree A, and the only reasonable hypothesis is that it had not yet reached the base, owing to poor insolatjon, thick bark, and age of the tree. Growth ‘in lateral branches With a view of adding something further of value to the manner of growth procedure in Pinus rigida, investigations were also -car- ried on upon certain of the lateral branches. Cuttings were taken from each year’s growth until the main axis was reached. Then incisions were made 20cm. above and a like distance below the point where the branch joined the main axis. Growth in the branches followed the same rule as in the main axis. It commences some distance back of the apical shoot and spreads gradually in both directions. Time of awakening in the apical shoots of the 1912] BROWN—PINUS RIGIDA 395 branches, at least in the case of trees standing in the open, appears to be identical with that in the apical shoot of the main axis. Cuttings taken May 4 showed about the same amount of growth in each case. The time of the beginning of cambial activity at the base of the branches is of interest when compared with that of the main trunk. Fig. 11 shows a section from the base of a limb six years old. Fig. 10 is from a cutting taken from the main axis just above the branch, and fig. 12 a like distance below. Growth is most advanced in fig. 12, present in fig. 10, but lacking to all appearances in fig. 11. Cuttings taken from the limb in question showed growth in evidence to the extent of one or two tracheids (out to and including the apical shoot). It follows from the above that growth at the base of the branches is more retarded than at neighboring spots in the main axis. It proceeds more rapidly in the latter than it does in the former, so that it is often in evidence in the main axis before it makes its appearance at the base of the branches. This may be due to the more rapid rise of solutions in the trunk, although further investigation is necessary to decide that point. Rate of procedure Having determined the general procedure of growth in Pinus rigida, observations were next made on the rate of procedure. In order to make estimates of this, the series of cuttings of 1909 on tree II were employed. There were four sets of these of twelve each. In each set the amount of wood formed for the individual section was determined as nearly as possible with a micrometer scale, and the results tabulated on a basis of 100 (table I). The number of days intervening between each observation are given as well as the total gain and average gain per day; x implies cutting was a failure; -+ signifies width at least as much as given; ? indicates apparent loss due to local growth fluctuation. The table is of value in leading us to certain general conclusions. On May 13, the width of the new-formed ring was greatest in cut- tings 4-6. It gradually dwindled in size toward the apical shoot, while below there appeared to be a decline followed by an increase. The next investigation was made on May 25, twelve days later. 396 BOTANICAL GAZETTE [NOVEMBER TABLE I No. Gain No. Gain No. Gain No. |Amount |Amount| of |Gain}| per j|Amount| of |Gain| per |Amount| of |Gain| per days day days day days day May | May June June 13, 09/29, ’o9 3, 09 15, 09 [ 3 5 12 2 | 0.17 5 9| O] 29.00} 35 I2 | 30 | 2.50 2 3 5 12 2| 0.17 20 9] 15 | 1.63 25+| 12 5 | 0.42 3 8 8 12 © | 0.00 24 9} 16}; 1.78 x 12 x x 4 12 15 | 12] 3]0.25 |} 40 9] 25 | 2.78] 35 | 12 ? 9 5 12 18 12} 6]0.50j; 30 9; 12] 1.334; 40 I2 | 10 | 0.83 6 12 20 | 12] 8] 0.67] 30 9] 10] r.1r | 35 12 | 5 | 0.42 7 8 13 I2] 5]0.42] 4o 91 27] 3 40 | 12] 0} 0.00 8 x Io | 12] # x 30 9 | 20] 2.22] 38 I2 8 | 0.67 9 8 It I2} 3]0.25] go 9] 29 | 3.22] 45 12 5 | 0.42 Io 6 io | 12] 4] 0.34] ar 9 | 11] 1.22! 30 | 12] 9g | 0.75 II x x I2] 4 x 25 9| « x 42 I2 | 17] 1.42 12 Ir 8 | 12 P x x o| « x 17 12} «| « Looking at the average gain per day, we see that in cutting 6 the greatest increase occurred, while above and below the amount of gain varied irregularly with the different cuttings. However, the gain in the apical shoot was but slight. Comparing the results of May 25 with those of June 3, it is evident that, with the excep- tion of the apical shoot, the average daily increase at the latter date was greater in every case than in the former. In other words, the tree grew faster in diameter, with the exception of the terminal shoot, during the last of May and the first of June than before that time. It follows from the table that the rate of increase varies considerably with the cutting and obeys no general law. The data of June 15, howevey, are most interesting. There was a decrease in the rate of growth between June 3 and June rs, with the exception of the apical shoot. Here, on the contrary, the gain in 12 days was 15 times as great as that of all the diameter growth previous to June 3. There was then a very marked increase in the formation of the annual ring at this point as compared with the gradual decrease in the remainder of the tree. Unfortunately, however, data are not available bearing on the rate of elongation of the apical shoot. It would appear, however, that its elongation must have been very rapid up to June 3, so much so in fact that the increase in the width of the annual ring could not result. From June 3 to June 15 the rate of elongation probably decreased appre- 1912] BROWN—PINUS RIGIDA 397 ciably, while greater increase of wood formation resulted as a natural sequence. Before summing up the results of the preceding paragraph, some observation on cessation of cambial activity should be given. It has long been recognized that while cambial activity makes itself manifest in many trees at about the same time, there is no relation evident in its cessation. Thus Buckwout (2) found in Larix decidua that there was little if any growth after July, while Pinus Strobus continued to form wood until well into September. R. Hartic (6, 7) also gives data bearing on this subject. In beech it lasts 2.5 months, in oak 4 months, in Scotch pine and Norway spruce 3 months. FRIEDRICH (see WIELER 14), on the contrary, claims that in coniferous and hard woods in general there are two periods of growth, one lasting until about the end of May, sinking until the middle of June, and reaching a maximum again in July. Complete cessation resulted by the middle of August. The majority of workers, however, unite with Hartic in saying that cessation of cambial activity varies greatly with the species con- cerned. In the present studies, the latest cuttings in 1909 were made on July 6 upon tree III. At that time growth was still in progress throughout. Comparing these with cuttings taken from the same tree on February 21 of the next year, the following interesting results are obtained. Cutting 2 showed 0.5 of the ring complete, cutting 4, 0.6, cutting 8, 0.85. R. Harric (6) agrees with T. Hartic (8) that cessation of growth begins first in the crown in trees in open stand and proceeds gradually downward. If such is the case, the data just given present an anomaly, or else growth was accelerated in the apical portions after June 15. However some of Hartic’s data are in accordance with that already given. For example (BUSGEN 3), on June 21 the ring of an oak as compared to that of a previous year gave the following data: At 1.3m. height........ 0.45 complete At 3.5m. height........ 0.45 complete At 5.7m. height........ 0.45 complete At 7.9m. height........ 0.72 complete At 12.3 m. height........ 0.57 complete At 14.5 m. height........ 0.56 complete (3-4 year branch) 398 BOTANICAL GAZETTE [NOVEMBER Hartic then obtained results comparable to the present ones; that is, at about the middle of June he observed that growth was most advanced near the middle of the tree and decreased in both directions from that point. And yet he persists in his assertion that growth ceases in trees in open stand first in the youngest branches. Such being the case, the only possible solution of the data given above is that there must have been a marked accelera- tion of growth in the apical portions after June 21 and a corre- sponding decrease in the parts below. Whether the same applies in the pitch pine further investigation must decide. There was an increase in radial growth in the apical shoot and at the same time a decrease below between June 3 and 15, but that growth ceased first above cannot be deduced from the present observations. As regards the theory advanced by FRIEDRICH concerning two periods of maximum growth in trees, little can be said. The second period if present in Pinus rigida must be the minor one, inasmuch as the ring was on an average more than half completed on June 15. Width of the ring Measurements were made from sections of tree III to determine the width of the ring at different heights. According to Harrtic, in trees in open stand the amount of wood formed increases from apex to base. This may arise from one of two alternatives; either the annual ring may decrease in size owing to the increasing diame- ter, or the reverse may be true. The latter, he says, is but rarely the case and sometimes oecurs in trees which are exceptionally well nourished, that is, those possessing a large vigorous crown. From these observations it is to be expected that in Pinus rigida the ring would increase perceptibly in width toward the base, inasmuch as the crown is as a rule not exceptionally well developed. Such was , the case. At cuttings 1 and 4, the completed ring on February 21, 1910, was about the same width. At cutting 8 it was but 0.85 the size of that above, while cutting 12 showed a still further decrease too.70. It follows that in Pinus rigida, if there is such a decrease in the size of the ring from apex downward in young vigorous growing trees, the same applies with even greater force in older trees with longer axis and poorly developed crown. 192] BROWN—PINUS RIGIDA 399 The living portion of the cortex, on the contrary, follows a law exactly the reverse. In the upper portions of the crown the cortex is necessarily thin, inasmuch as it contains a relatively small series of bast parenchyma and sieve tube areas. Below, the thickness of the cortex increases markedly, so much so in fact that it often attains 3-5 cm. in width. The storing capacity of the cortex as a result must be greatest in the basal portions of the trunk. Assum- ing that food abundance alone was concerned in cambial awakening, the latter would result first below. Inasmuch as it does not, there are certainly other determining factors; chief among which is probably insolation. Investigations on the older trees revealed a number of factors -of sufficient interest to demand mention in this paper. A curious feature long known to former workers was especially prevalent. I refer to the often noted lessened density of the wood on the south side of trees. This is due to the fact that the proportion of summer wood on the north side is greater as compared with the width of the ring than on the south side. This disparity in wood formation, however, is not so marked in young individuals. The ring forma- tion is much more regular and it is only in the older trees that the phenomenon above described is seen. As to the cause of this lessened density on the south side, no reasonable conclusion was attained in these investigations, nor has it ever been satisfactorily accounted for. It is without doubt correlated with insolation in some way, but further study is necessary to determine this def- nitely. The manner of cambial awakening likewise presents an interest- ing study. It was observed that even on different sides of the same section a noticeable disparity often occurred. In some cases growth had proceeded to the extent of one or two partly formed tracheids, while in closely neighboring spots the cambium appeared as yet in the resting condition. Nor was one tracheid completely formed as to size before another began. Often rows of three or four small tracheids were visible, none of which had yet attained half the size of those formed first the previous year. In such cases it would appear that cell division was so rapid in the cambial region during favorable seasons that new elements were laid down before 400 BOTANICAL GAZETTE [NOVEMBER their predecessors had yet attained their maximum size and strength. Double rings were often in evidence in the old trees. These might easily cause miscalculation as to age. The phenomenon of double ring formation has often been observed, especially in broad- leaved trees. Here it was ascribed sometimes to partial or com- plete defoliation, at others to favorable or unfavorable external factors. The first assumption would not hold in Pinus rigida in this case or in general, since defoliation rarely occurs. The cause must be ascribed to external growth conditions, but what these are would be difficult to determine. That they are most prevalent in old trees is well known, and this would lead one to infer that their formation is in some manner correlated with inhibition of growth, since the effects of this are most marked on older less vigorous individuals. Secondary thickening in the roots Little stress was put on the study of secondary root thickening in the present investigation. Only one cutting was taken, on April 27, 1910, for purposes of comparison, so that no reliable deductions can be made. At this time cambial activity was not manifest, although it must have been in process throughout the aerial portion with the possible exception of the apical shoot. T. Hartic (8) claimed that cambial awakening in the roots is much later than in the aerial portions. He gave midsummer as the time of first inception and said it continued far into October. Whether the same applies fo Pinus rigida further investigation only can decide. Suffice it to say, however, that the growth in thickness of roots must not be confused with growth in length. The latter is manifest often as early as March and continues throughout the season. Summary 1. The histological characters of Pinus rigida present no wide variation from the normal coniferous type. 2. The secondary thickening in the root is similar to that in the stem, but differs (a) in less sharp demarcation between the annual rings, (b) in the biseriate character of tracheids, and (c) in less density. r912] BROWN—PINUS RIGIDA 4or 3. Growth began in young 20-30-year old specimens of Pinus rigida in the vicinity of Ithaca as early as April 15. While there was no direct evidence of cambial awakening secured the previous year, sections taken at a later date showed growth in such an advanced state that it must have begun fully as early. 4. In older trees cambial awakening is sometimes retarded at the base where proper insolation is lacking. 5. There is no appreciable difference in the time of cambial awakening on the north and south sides of trees. 6. Growth began first in 20-25-year-old specimens at some dis- ‘tance below the apical shoot, but during a period of 19 days gradually spread upward until it reached the apex of the trees. 7. Investigations on trees A, B, and C tend to show that growth in older individuals begins first in the crown and spreads downward. The time of its inception at the base varies with conditions of insolation, bark, etc. 8. Growth in the branches follows the same rule as in the main axis. The time of awakening in the former is almost if not abso- lutely identical with that in the latter. 9. Growth spreads down the main axis faster than it does tong | the lateral shoots. a! io. Except in the terminal shoot, growth in diameter was more rapid between May 25 and June 6. In the terminal shoot itself greatest rapidity of growth was manifested between June 6 and June 15. 11. No reliable deductions concerning cessation of cambial activity can be drawn from the present investigations. 12. The width of the complete ring decreases from apex to base; the living portion of the cortex follows the reverse rule. 13. A number of peculiarities already noted by others are preva- lent in mature specimens. These are (a) lessened density of wood on the south side of trees, (0) irregularity of cambial awakening in closely neighboring parts of the same section, (c) successive forma- tion of new elements before previous ones have reached their maximum size, and (d) double rings. CorNnELL UNIVERSITY Irnaca, N.Y. 402 BOTANICAL GAZETTE [NOVEMBER LITERATURE CITED 1. Britton, N. L., North American trees. 1908. p. 31. 2. BuckHout, W. H., Formation of annual rings of wood. Forest Quarterly 53259. 1907. . Biscen, M., Bau und Leben unserer Waldbiume. 1897. p. 62. Coutter, J. M., and CHamBERtalIn, C. J., Seed plants. rgor. . Gorr, E. §., The resumption of root growth in spring. Wis. Sta. Rept. 1898: 220-228. fig. 6. 1898. . Hartic, R., Das Holz der deutschen Nadelwaldbiume. 1885. p. 35. , Anatomie und Physiologie der Pflanzen. 1891. p. 262. . Hartic, T., Bot. Zeit. 18:829. 1858. - . Hastines, G. T., When increase in thickness begins in trees. Science, N.S. 122585. I9g00. ro. Mer, E., Sur les causes de variation de la densité des bois. Bull. Soc. Bot. France 39:95. 1892. Ir. PENHALLOW, D. P., Anatomy of the North American Coniferales with certain exotic species from Japan and Australia. Amer.’Nat. 38:243. 1904. 12. Reuss, H., Beitr. zur Wachstumsthiatigkeit des Baumes nach praktischen Beobachtungsdaten des laufenden Starkenzuwachsganges an der Sommer- rinde. Forstlich. Zeitschr. 2:145. 1893. 13. STRASBURGER, E., Die Angiospermen und die Gymnospermen. 1879. 14. Wreter, A., Uber die Periodizitat im Dickenwachstum des Holzkérpers der Baume. Bot. Zeit. 56: 262. 1898. pw CMD EXPLANATION OF PLATES XXIV AND XXV Fic. 1.—Cutting taken from apical shoot of tree III April 15, 1910; cambium in the resting condition; X 50. Fic. 2.—Same, but cutting taken about 1 m. from the apex; cambium in the resting condition; X50. * Fic. 3.—Same, but cutting taken about 2m. from the apex; growth in evidence to the extent of one or two partly formed tracheids; X50. Fic. 4.—Cutting taken from apical shoot of tree III May 4, 1910; growth just beginning at A; compare with fig. 1; X50. ' Fic. 5.—Same, but cutting taken 1m. from the apex; growth slightly more advanced; compare with fig. 2; X 50. .Fic. 6.—Same, but cutting taken from the apex; growth in evidence to the amount of 3 or 4 tracheids; compare with fig. 3; X50. Fic. 7.—Cutting taken from tree III April 15, 1910, about 3 m. from the apex; growth in evidence to the extent of one or two partly formed tracheids;. X50. Fic. 8.—Same, but cutting taken about 4m. from the apex; growth in evidence to about the same extent as in fig. 7; X50. XXIV PLATE BOTANICAL GAZETTE, LIV iJ ee Coal Ss og a: mg % \ eS be “) %) cy ‘) Si SI Se Nad? ~ BROWN on PINUS RIGIDA PLATE XXV BOLANICAL GAZETTE, LIV 12 ll BROWN on PINUS RIGIDA 1912] BROWN—PINUS RIGIDA 403 Fic. 9.—Same, but cutting taken about 5 m. from the apex; cambium in the resting condition; X 50. Fic. 10.—Cutting from main axis of tree VI April 22, 1910, at a distance of 3m. from the apex; growth in evidence to the extent of several rows of partially formed tracheids; X50. Fic. 11.—Same, but cutting from the base of a lateral branch which entered the main axis 20cm. below cutting shown in fig. 10; no growth in evidence; X 50. Fic. 12.—Same, but cutting taken 40 cm. below that in fig. 10; growth in evidence to the extent of several rows of tracheids; X50. GROWTH STUDIES IN FOREST TREES (wire. PLATES “xiit. AND XIV ‘AND, TWO: GRAPHS): H.P. BROWN’ - Reprinted for private circulation from “THe Rodanneut Gazette, Vol. LEX, No: 3,: “March ror GROWTH STUDIES IN FOREST TREES 2. PINUS STROBUS L. H. P. Brown Object and scope of the investigation (WITH PLATES XIII AND XIV AND TWO GRAPHS) The present paper is the second of a series presenting the results of studies of growth in forest trees.t The investigations are planned with a twofold purpose, namely to clear up some dis- puted points regarding the formation of annual rings and to out- line the laws of growth in trees. The results of the studies of Pinus Strobus L. are presented in this paper. Pinus Strobus L. (white or Weymouth pine) was chosen for the second subject of investigation for several important reasons. First, it is a soft pine and differs from the hard pines, which include Pinus rigida Mill., both in external as well as internal anatomy. Further, it is more rapid in its growth than pitch pine, and inter- esting results were anticipated from a comparative study of the two trees. Finally, white pine is of recognized commercial impor- tance, and it is hoped that some of the conclusions will prove of interest and value to foresters. The specimens in the investigations, aside from the seedlings, were all in the wild state. The investigations were not limited to a few trees or to one locality. Specimens were examined in different woodlots, thereby providing variation in site, soil, and other silvicultural conditions. Seedlings from the nursery beds of the Department of Forestry, N.Y. State College of Agriculture, Cornell University, small trees from the same, as well as others in the wild state, and older trees which had passed the century mark and presented wide variation in crown development, were all sub- jected to examination. Fully 50 specimens were studied and from them comparative data were secured. It is hoped that the results thus obtained will prove of permanent value in formulating general t The first paper appeared in Bor. Gaz. 54: 386-403. 1912, and included the inves- tigations upon Pinus rigida Mill. 197] [Botanical Gazette, vol. 59 198 BOTANICAL GAZETTE [MARCH rules of growth for the species. Inasmuch as a description of all the trees used would be confusing, short silvicultural notes on each specimen will be given in the text where it seems necessary. Previous investigations of growth in forest trees Before entering upon a description of the methods employed in this work, a brief résumé of those of other investigators will perhaps add interest to the present study. Von Mout (25) sought to determine the growth of trees by making measurements of the circumference at a definite place on the bole. From these the radius was computed and the increase in thickness noted. CHRISTISON (5) pursued the same method and computed data for a large number of species, including both hard and soft woods. The data of Jost (13) were based in part on the methods given above and in part on measurements which he obtained by the use of a ‘‘Fuhlhebel.”? Any data secured through bark measurement are unreliable because of continual changes going on in the older parts of the secondary cortex and changes which bear no relation to the newly forming rings. As a result, only broad generalizations can be drawn from data based on such methods. T. Hartic (12) sought to determine the growth of tree species in a different manner. Choosing even-aged, pure stands, where growth conditions appeared to be similar, he felled typical speci- mens from these at different periods and made comparative studies. He assumed that in such stands all individuals exhibited similar characteristics of growth, a view that is untenable in the light of our present knowledge. Harric’s method is open to criticism in that it was extremely inaccurate and could therefore never give reliable results. ‘Growth varies markedly not only in different individuals in a stand, but also in different parts of the ring at a given height. MISCHKE (24) took the first steps in the direction of securing accurate results. Using an increment borer, he studied the annual ring at different periods in its development and obtained in this way the first results which were in any way accurate. WUIELER (39) 2 For description see reference. t915] BROWN—PINUS STROBUS 199 also followed this method and made many consecutive borings on coniferous and broad-leaved trees. His observations led him to infer that growth is very irregular not only as between different trees, but at different places in the same tree. The last named method, however, is subject to errors, and the results of WIELER show wherein it is inaccurate. When a boring is made with Pressler’s increment borer, it is impossible to avoid applying some pressure to the wood core which is to be removed. During rapid growth (fig. 4) the elements of the newly formed xylem are thin- walled and easily crushed and displaced by pressure, however slight. The partially formed ring when treated in this manner may easily show a wide variability in diameter and thus lead to grossly erroneous results. This appears in part to explain why WIELER inferred that in neighboring areas growth varies consider- ably. I have already pointed out (1) that slight differences occur in neighboring areas, and the present investigation leads to the same conclusion, but the marked discrepancies in growth which WIELER describes are not present in either of the pines which have been examined. Histological technique The methods pursued were in general those followed in 1910. The technique, however, has been improved as the time and place to secure the best material became more evident with increasing experience. The chief objection is that it is necessary to make rather large wounds on the trees. This objection is not so serious, however,'in coniferous trees because the resin which exudes prevents quite efficiently the drying out of the tissues. The investigations on white pine began in August 1912, and continued until October 1913. Incisions were made on trees at intervals from base to crown (as high as it was safe to go in tall trees). Unless otherwise stated, these were always on the south side of the tree. A few cuttings were made on the north side for comparative purposes. Cuttings from branches at intervals were also made, and, unless stated otherwise, were lateral on the branch. Each cutting included all or a portion of the inner bark, the cam- bium, and all of the preceding year’s ring except toward the end 200 BOTANICAL GAZETTE [MARCH of the season, when the growth of the years had attained such thickness as to make this impracticable. Duplicate cuttings were made on several trees at intervals of time varying from a few days to several weeks. These were always near the former cuttings and lateral to them. Rarely were the duplicate cuttings more than a few inches from the original ones. One series began in August tg12 and continued into September of the following year, cuttings being taken at least every month. The material, as soon as obtained, was properly labeled and fixed in Gilson’s fixer of the usual strength. Then after thorough washing it was run up through the lower grades of alcohol and stored in 65 per cent alcohol until wanted. The above corresponds to the methods used in 1910. From this point the procedure varied depending on the object in view. When it was desirable to know the extent to which growth had progressed, or the abundance of starchy material present, freehand sections were made with a sharp razor. These were dyed with temporary stains and then studied. The HCl-phloroglucin stain for lignin, followed by the permanent Haidenhain’s iron- hematoxylin stain for cellulose, gave excellent results. With this combination the extent of growth could be measured and esti- mated with accuracy. Chlor-zinc-iodide, as well as various com- binations of I-KI, were occasionally used. For minute examination of the tissues greater care was taken in manipulation. The material was demineralized with hydro- fluoric acid and imbedded in celloidin. Sections were obtained in this manner 10-15 thin, which served the purposes of the investigation. Extensive and comparative histological studies were then made and the results tabulated. The method described above makes it possible to follow the progress of the growth. One obstacle which could not be over- come was the inaccessibility of all parts of standing trees. In order to check up the results obtained, several trees of different ages were felled during the growing season. Accurate stem analyses were made of these and the progress of growth was observed throughout the tree. These data were then compared with those obtained from standing trees. 1915] BROWN—PINUS STROBUS 201 Investigations on the roots of trees were attempted and gave some results worth noting. The roots were secured from young trees (about 30 years). Other root studies were made on seedlings from the nursery. A few cuttings were taken from the roots of old trees where they were exposed near the base of the bole. Microscopical characters of the xylem The xylem of white pine is so well known that it is unnecessary to describe it here. When contrasted with the wood of pitch pine, the xylem of white pine differs in a number of anatomical features. The upper and lower walls of the ray tracheids are smooth as compared with the dentate ones of Pinus rigida. Bordered pits occur on the tangential walls of the late wood, while they are lacking apparently in pitch pine. The transition between early and late wood is not so abrupt in white pine and the rings are generally wider. White pine is a more thrifty tree, and the present observations tend to show that it is more susceptible to changes of site, soil, etc., than pitch pine. This is exceedingly important from the economic standpoint. The roots of white pine exhibit the usual features of the roots of Abietineae. Diarch, triarch, and tetrarch roots are common. The root of seedlings is usually diarch (fig. 8), but the number of xylem rays is as a rule soon increased to three or four.3 Vigorous roots from thrifty trees between 15 and 30 years of age were pre- vailingly tetrarch, so that it would appear as if the number of xylem rays is correlated in some way with the amount of moisture available to the root and to the root environment, whether favorable or otherwise. VAN TiEGHEM (34) has noted this same variability in Pinus, Abies, and other allied genera, and further has pointed “out that no constant relation prevails between the number of xylem rays and the number of cotyledons. Not only does the number of xylem rays vary in roots of different ages, but the number may increase or decrease during the growing season. This is strong evidence that environmental conditions influence within 3 Each xylem ray is terminated centrifugally by a resin canal, and the oli- garchy of young roots can in this way be easily determined in cross-section with the naked eye. 202 BOTANICAL GAZETTE [MARCH certain limits the number of xylem rays. In general the larger the diameter of a yearling root, the greater the number of rays up to four. A pentarch or hexarch arrangement was not observéd in any case, although it may occur, since VAN TIEGHEM (0. cit. p. 7) reports the number as high as 7 in Scotch pine (P. silvestris). The xylem in old roots is comparable to that in the aerial parts of the tree, but differs in several well known particulars. The tracheids in roots have wider lumina and thinner walls and are never as well lignified as those in the parts above ground. This is especially well seen in cross-sections. In roots late wood formation is not as pronounced, owing no doubt to a decrease in mechanical strain in underground parts. The bordered pits on the tracheid walls, in both roots and stems, are mainly radially arranged. The uniseriate arrangement is here and there interrupted by the pairing of some pits. Further, the bordered pits in roots are larger than in the xylem of aerial parts. It is of interest to note in this connec- tion that wherever an old root becomes exposed it usually presents xylem typical of aerial parts, so that only underground parts exhibit the characteristics above described.‘ Winter condition’of secondary cortex and cambium’ The secondary cortex of white pine is very similar to that of pitch pine. It presents the same radial arrangement of the ele- ments, this arrangement becoming less regular as they are pushed to the outside (fig. 1). Companion cells are totally lacking, but one distinct row and a few scattered bast parenchyma cells are formed each year as in pitch pine, and these indicate the annual phloem areas in the old cortex. Occasionally the phloem pa- renchyma becomes crystallogenous, but never attains the size of that of pitch pine. The marked differences which exist between the bark of white pine and pitch pine are not present in the young phloem, but are caused by changes which take place subsequently in the outer cortex. 4 Kny (20) has pointed out the same structure in P. silvestris, and found that it was especially pronounced on the underside of large roots which had been exposed through erosion. 5 The notes only include observations on the winter condition of aerial parts, as underground parts were not accessible at this time of the year. tor5] BROWN—PINUS STROBUS 203 The resting cambium as seen in cross-section consists of 2-10 layers of tabular cells lying just outside the last formed xylem elements. Sano and other early anatomists considered the cam- bium as consisting of a single initial layer, which through repeated division gave off daughter cells centripetally and centrifugally. These divided a second time, and the resulting cells enlarged and became elements of the phloem or xylem. The initial layer, if present in white pine, cannot be distinguished as such. The cells in each layer of the merismatic tissue are similar to the others in size, form, and protoplasmic content. The number of layers of cells in the cambium apparently varies between rather wide limits. Such variability might lead one to think that the work was not accurately done. The figures given above are as exact as the material permitted. The cambium is a very variable tissue both in number of cell layers and thickness of the same. Data indicating this (table A) were computed from measurements on tree I, a description of which follows. Tree I was a thrifty specimen of white pine standing near the edge of a mixed stand on the brow of an incline which sloped north- ward into Six Mile Creek valley. The height of the tree was 55 feet, and crown development extended to within 18 feet of the ground. The tree was directly exposed to the south. Ground cover included sparse brush and pronounced sod formation. Cut- tings were first made on this tree in August 1912, at heights of 4, 17, 30, and 43 feet from the ground, and were repeated at frequent intervals until September 1913, as recorded in the tables. Twig cuttings from near the top of the crown were also taken from time to time. The data in the table are from the cuttings of February 20, 1913. TABLE A WINTER CONDITION OF CAMBIUM, TREE I Cutting Thickness of cambium | Cell rows in cambium eee 2 year twig........ 5- OF 2-4 691.04 6 year twig....... 5-9 2- 4 661.0 12 ft. from apex 29-31 6-7 3367.0 25 ft. from apex..... 32-40 7-9 4297.6 38 ft. from apex..... 290-35 7-10 3013.8 51 ft. from apex..... 20-35 7-9 2894.0 204. BOTANICAL GAZETTE [MARCH It follows from the table that in white pine trees which are growing rapidly, the cambium is smallest both in number of cells and thickness in the smaller twigs and branches. It increases gradually in thickness and number of cell layers until that point is reached in the bole where diameter growth is a maximum. The decrease in the figures indicating the dimensions of the cambium are not proportional thereafter with the decrease in growth in, diameter. It would appear as if the cambial layer, once it had attained its largest proportions, varied little in vigorous trees. In suppressed trees, however, it may reasonably be assumed that the cambial layers fall off in number and thickness toward the base of the shaft, but in such cases the reduction is not closely correlated with decrease in the width of the completed annual ring. Another point relating to the cambial and phloem tissues deserves description here. I refer to the statement commonly made in textbooks that while the formation of xylem ceases early, the cambium continues to form phloem as long as climatic condi- tions are favorable. It is of interest to note in this connection the condition of the young phloem and cambium on September 26, rgi2, and February 22, 1913. In all four cuttings of the first named date we find the condition as shown in fig. 7. Xylem forma- tion had apparently ceased, the cell walls in the last row of tracheids were still in the process of thickening, but no new elements were being added. In the phloem we find a broad band of sieve tubes with a few parenchyma cells interspersed among them, making up in all some 15 rows of cells. This represents, with the possible addition of two or three rows of partly crushed elements to the outside, the seasonal growth of phloem. It is to be noted here that none or very little compression had occurred. Comparing the above with what occurred on February 20, 1913 (figs. 2 and 3), the following interesting changes are to be found. Contraction had taken place, due to low temperatures during the winter, but not all of the sieve tubes are flattened to the same extent. In each of the four cuttings of February 22, the 3-5 last formed sieve tubes are only partially distorted by pressure, and those in the higher cutting (fig. 2) noticeably more so than in the lower cutting (fig. 3). In the last case there is a sharp dividing 1915] BROWN—PINUS STROBUS 205 line between the compressed sieve tubes and those which exhibit no compression, Further, as will be shown subsequently, the latter are the first sieve tubes to function the following spring. We may say that in white pine phloem development continues longer than xylem development. It only ceases with the extreme cold temperatures of December and January, and the tree makes no special provision for cessation of growth as in the xylem. Sieve tubes in all stages of arrested development may be found during the dormant period. General discussion of tree growth Growth as it occurs in trees falls logically into two subdivisions: growth in length and growth in thickness. In the first category we have only primary growth. It does not matter whether elongation is going on in root, stem, or leaf, it always has its inception in a growing point, and all tissues resulting from cell divisions in this apical meristem are primary tissues. Growth in thickness, on the other hand, results mainly from secondary thickening which is brought about through the activities of a perennial cambium. Tissues arising in this way are distinguished as secondary tissues in contrast to primary tissues.. The primary tissues, with the exception of the primary cortex, usually soon attain their full size in both coniferous and dicoty- ledonous trees, and in the majority of woody plants we may regard them, with the one exception mentioned, as mature at the end of the first growing season. Secondary growth, however, commonly begins the first year, and as a result the processes of primary and secondary thickening overlap, and both often go on at the same time in closely neighboring parts of the tree. Second- ary thickening may thus occasion alterations before all the primary tissues have reached the adult state. It is entirely conceivable, for example, that both categories of growth go on simultaneously in the terminal shoot of a pine or in a young root. In this connec- tion URSPRUNG (35) reports in certain cases the subsequent enlarge- ment of the pith after secondary thickening had begun, so without 6 It is only in woody monocotyledons and tree ferns that primary growth persists for any length of time. BOTANICAL GAZETTE [MARCH 206 doubt these two processes overlap. For the sake of clearness in the subsequent discussion, however, growth in length will be con- sidered in the general sense of primary growth, growth in thickness as secondary growth. Awakening of secondary growth in aerial parts’ The awakening of secondary growth in aerial parts is first manifested in the cambium and the adjacent phloem tissue. It is evident in all cases several weeks before actual cell division begins. The cambial cells and last formed sieve tubes (6-10) open out radially, so that they attain several times their former diameter. Reference to the following table will show the changes which occurred between February 22, 1913 and March 29, 1913, in the width of cambium and last formed phloem. TABLE B GROWTH WITHOUT CELL DIVISION, TREE I Cutting wailed 23) eer Per cent increase se ae foe Loi eeieiee 69.0" O1.5# 32.6 013.3 49.7 Desh aerate 89.1 110.6 24.0 182.9 105.3 TED, secanss- cess 94.4 140.7 70.0 180.4 81.0 Whogsnacac 103.3 171.1 56.0 188.5, 82.0 In all cases, enlargement of the tissues in question occurred between the first two dates, and amounted from over a quarter to nearly three-quarters of their original size. The place of greatest enlargement was in cutting III, 17 feet from the ground. This does not correspond with the place of greatest ring thickening (table A) the previous year. Whether any significance can be attached to this discrepancy cannot be decided with certainty. It seems reasonable, however, to ascribe it to heightened temperature from the rise of soil water in the xylem. It would be natural to assume 7 No observations have been made on secondary growth in the leaves. MEISSNER (21) has observed a marked increase in the number of phloem elements and a very slight increase in the xylem elements in a number of species of Pinus. § Rost. Hartic (11, p. 262) made note of the temperature of soil water as a factor potent in forwarding growth. 1915] BROWN—PINUS STROBUS 207 that the greatest increase would be in cutting II. However, as this was 30 feet above the ground, it is quite possible that the tissues there had not yet experienced the increase in temperature due to the rise of soil water in the trunk. . The present investigation gives no reliable data as to where the first phloem activity was manifest. It had occurred throughout the tree on March 29, 1913. The awakening of growth began in this one specimen before the first of April and was not accompanied by cell division. Soil water was apparently largely instrumental in its inception. If we refer again to table B for the data for April 12, 1913, two weeks later, we may draw the following interesting conclusions. The greatest diameter increase at this time is in cutting II, where it has been over 100 per cent. In other words, the ascending soil water may have reached the point of greatest growth (because the previous year’s ring was widest here) and caused a rapid expansion of the tissues. In cuttings III and IV we find an apparent reversal of the foregoing conditions. Cutting III has increased only 11 per cent during the same period, while in cutting IV we find the increase has been 26 percent. This may be ascribed to two causes, either one or both of which may be responsible. While the increased tempera- tures may have prevailed longer in IV than in III, the amount of reserve food material available was not as great. As a result, growth in cutting IV may have been retarded more than it was in cutting III; or cell division may have occurred in some of the cut- tings and upset the equilibrium. Careful counts were made to find the number of cells in the cambium and last formed phloem in all four cuttings of March 29 and April 12. While slight differ- ences occurred, these were not such as to warrant the conclusion that cell division had taken place between the two dates. The changes which occurred between March 29 and April 12 were due solely to enlargement of cells already present. We must ' infer then that the apparent contradictions of the figures in table B are due to differences of available food in different parts of the tree. Cell division had begun in tree I by April 26. At this time the activity was manifest in cutting I (table C). Here some 8-12 tracheids and 2 or 3 new sieve tubes were already formed. Wall 208 BOTANICAL GAZETTE [MARCH thickening had not begun in the new tracheids, but was noticeable in the first of the new sieve tubes. Cutting II exhibited only slight evidences of cell division, while in cutting III growth was well started. No division had yet occurred in cutting IV. Growth had been very rapid in cuttings I and III, as evinced by the absence of thickening of the cell wall. This may be accounted for in part by the high temperatures which prevailed between April 22 and 26. During that period the mean daily temperatures ranged from 52° to 70°F. Precipitation amounted to only 0.03 inch, but large amounts of ground water were available at that season. TABLE C BEGINNING OF GROWTH BY CELL DIVISION, TREE I,-APRIL 26, 1913 Cutting Growth Number of | Wall thickening |New sieve tubes Promawaga ss adigemaneneas hale Present 8-12 None 2-3 Le. ssveseyecenaeceansases Indication o- 1 None o-l DU lex ek teas eRaORAO DES Present 6-9 None 1-2(?) WV vedo eee hG044 ashes None ° None ° To explain plausibly the conditions in cutting IT, the point of greatest growth the preceding season (table H), is not an easy task. Every indication seems to show that we might expect most rapid growth at this point. We can conclude only that the restricted growth here denotes one of the many idiosyncrasies of tree growth, where, as pginted out by WIELER (38), marked differences may occur in closely neighboring spots. It is to be expected that growth would not be manifest in cutting IV at this early date, so we may conclude that in tree I cell division was in evidence on April 26 in the upper portion of the bole but had not yet begun at the base. In-order to check the results on tree I, four bole cuttings, including the terminal leader and four branch cuttings, were made on a neighboring tree on May 4, 1913, eight days later. Tree II stood about 10 feet from tree I, and was apparently of the same age and subject to the same silvicultural conditions. The extent of growth and lignification in this individual is given in table D. 1915] BROWN—PINUS STROBUS 209 It follows from table D that on May 4 cell division was going on in all parts of the bole on the south side of the tree, with the It was farthest advanced in cuttings II and III, as might be expected, because the last formed annual ring was thicker here than in the basal cutting. exception of the terminal leader. TABLE D EXTENT OF GROWTH IN TREE u, May 4, 1913 A Number of A tof Cutting teecheds | lignitcation Remarks I. Terminal leader, 1 year’s TOW UN oenes0 dasa a earaccn te ’s None None Phloem active; no cell division I. Same, 2 years’ growth.... I- 2 None Same as above II. 44 feet above ground ... 12-15 1-3 tracheids| New phloem elements. cell division IIT. 33 feet above ground .. 12-15 1-2 tracheids| Same as above IV. 5 feet above ground.... 10-12 None Same as above The branch cuttings were made on a branch which ran out some 20 feet in a southeasterly direction at a distance of 13 feet above the ground. Five cuttings were taken at intervals of about 4feet. In cutting I (beginning from the tip) no tracheid formation was evident. In cuttings II and III tracheid formation was in progress, while in IV and V (basal) enlargement of the tissues had occurred, but no cell division. Cell division in the branches was similar to that in the bole, but more sluggish. It begins back of the branch leader and is most tardy in the base and leader of the branch. Which of the last is the first to exhibit growth depends on the length and vigor of the branch. Numerous other observations were made on trees of different ages and different localities. It was found that cell division may be in progress some time in the upper portions of a tree while it is totally lacking below. This applies especially in old mature trees in closed stands, where growth is proceeding very slowly. Further, in general cell division first begins on the south side of the tree and in the basal portions. This peculiarity, due apparently to insola- tion, has also been observed in some cases in pitch pine (1). It was noted in reviewing the literature on tree growth, that some (14) have attempted to correlate growth awakening with / ( 210 BOTANICAL GAZETTE [MARCH the opening of the buds and the formation of new leaves. With this point in view, measurements were made on a young white | pine stand of natural origin on May 3, 1913. The trees varied in age from 4 to 11 years and were in a thrifty, vigorous condition. On this date the buds were found to have opened and the young stems to have elongated 0.5—2.5 inches. All the growth in length had occurred in the preceding 10 days. Neighboring trees which were older showed less pronounced elongation of young parts; but growth had been in evidence in older, less favored trees since March 29, 1913, and cell division at least since April 20 of the same year. It follows, therefore, that growth in thickness begins before growth in length, and apparently, at the start at least, at the cost of reserve food material. No correlation exists between the two in white pine. Concerning the time of cambial awakening, the researches of others bear out the conclusions of this paper. Some of CHRIS- TISON’S (5) are given in table E. It should be noted, however, that CHRISTISON’S results were obtained from bark measurements and do not necessarily indicate xylem formation. TABLE E GROWTH AWAKENING IN CONIFEROUS SPECIES, EDINBURGH, SCOTLAND No. of tree Name Year Awakening of growth OF ted per nae aeuat Abies Lowiana 1890 April 6 OD) jax aasercksey aieeene Abies Lowiana 1888 April 16-30 O68. avo usenn apes pois Abies Douglasii 1890 April 20 Oh cuae sccmrmmma ena Abies Douglasii 1888 April 16-30 Ol seas say eee Kea eae Abies 1890 April 13 26s ge Agaeereeeaaex Pinus excelsa 1890 April 6 200 wees waeaeeas eae Pinus Pinaster 1890 May 3 BO ets cosa aune ales Cedrus africana 1888 April 16+30 MISCHKE (24) also made observations on this point, but did not include white pine among the species investigated. WIELER (39), however, examined three white pines in his experiments of 1894. Two of these were from a closed 40 year old stand, the third a 15 year old tree from another stand, all near Dresden, Germany. Growth was in evidence in the younger specimen to the extent of 13 or 14 tracheids on April 24. No growth occurred at the base of 1915] BROWN—PINUS STROBUS 2Ir the others until after the first of May, but growth must have been in evidence in the higher portions of the tree before that date. In the latitude of Dresden growth apparently starts fully as early as at Ithaca. Intensity of growth in aerial parts As already noted, growth continues some time before cell division occurs. It is first manifest through the enlargement of tissues already formed during the previous year. When cell division begins, it proceeds at first very rapidly, and in such a way that more elements are added to the inside of the cambium than to the outside. This was plainly observed in the sections and included in the data in table C. There 8-12 tracheids have been formed, as compared with 2 or 3 new sieve tubes. The cells thrown off to the outside gradually become transformed into sieve tubes, or more rarely into phloem parenchyma cells. This is accomplished in the first case through a thickening of the cell wall and the forma- tion of lateral sieve plates. The phloem parenchyma cells thicken their walls very little at first, but enlarge for several seasons and eventually attain a much larger size than the sieve tubes. In the outer bark their walls are often strongly lignified. Evidence of the rapidity of xylem formation is readily obtain- able in early May. It is not uncommon to find 10-15 tracheids fully formed (fig. 5) without any indication of thickening of the wall. Subsequently the thickening begins, and before it has progressed to any extent lignification is evident in the cell walls, as brought out by the phloroglucin-HCl reaction. Wall thicken- ing and lignification never start, however, until tracheids have attained their maximum dimensions as seen in cross-section. The rapidity of vernal growth in white pine is apparently contingent on three factors: (a) the amount of reserve food material, (6) moisture, and (c) temperature. The first is always at its optimum in the spring, as the abundance of starch in the storage tissues testifies. Moisture likewise, at this time of the year, is available long before the buds begin to open. GorF (8) has pointed out the early resumption of growth in the roots of coniferous plants, ‘and observations on white pine coincide with his results. The 212 BOTANICAL GAZETTE [MARCH first two factors, therefore, may be eliminated from the discussion because both are at an optimum in the spring. The temperature of the cambial layer depends, on the other hand, on three factors: (a) temperature of the air, (b) temperature of the soil water, and (c) direct insolation. Which of the three is most potent in the awakening and rapidity of cell division has not been determined, because they are so closely related to each other. It would appear that the temperature of the soil water plays a prominent part in the awakening of growth because of the opening out of the phloem first near the base of the tree. Factors (a) and (c) would be entirely negligible here, or at least play a minor part because of the thick layers of bark. Growth in the spring begins before factors (a) and (c) could have reached any appreciable height, so that the heat derived from soil water is certainly potential in awakening growth. It is quite impossible to separate factors (a) and (c) and to note their effect in all trees. However, cuttings secured from the north and south sides of isolated trees at the same height often afford ample evidence of the effect of insolation.2 Data were secured to bear out the foregoing statement as early as May 10, 1913. The tree examined was a “Wolf” white pine on the south side of Fall Creek beyond Forest Home, N.Y., a suburb of Ithaca. The speci- men was 51 feet high, with a diameter breast height of 15.3 inches, and exhibited vigorous growth in spite of the poor soil conditions. At the date mentioned, tracheid formation had proceeded on the south side to the extent of 12-14 tracheids, while on the north side g or 10 tracheids had been formed. Lignification had not as yet set in, although all but the last 3 or 4 tracheids formed had apparently attained their ultimate size. That direct insolation is potent in the awakening of growth in trees is certain. However, one indi- vidual will present occasionally conditions the reverse of what would be expected. It follows from the preceding paragraph that the awakening and the rapidity of growth depends on three factors, two of which are at an optimum in the spring and may therefore be neglected. ® Trees should be selected only from sites which are level, as trees growing on slopes are subjected to other factors which often overshadow the effect of insolation, 1915] ' BROWN—PINUS STROBUS 213 The third (temperature) is a variable one, and to this the rapidity of cell division is apparently directly proportional. Some idea of the rapidity with which the formation of tracheids may go on may be drawn from the following. Basal cuttings were taken from the south side of the “Wolf” tree already described on May 3 and May 1o, 1913. The first cutting showed no evidence of formation of tracheids, while the other, taken a week later, exhibited 7 tracheids in each row, complete as to size, with several smaller ones in process of formation. The growth in places farther up the stem must have been going on still more rapidly. While the period mentioned above was warm and humid and therefore espe- cially conducive to rapid growth, it may be safely assumed that in all white pine trees in the vicinity of Ithaca formation of tracheids is very rapid at the start. A large number may be formed in a relatively short time. Intensity of growth in aerial parts In the discussion which follows; the distinction between inten- sity of growth and amount of growth must be kept clearly in mind. The latter may be easily ascertained for the whole growing season or for any part thereof by measuring at a given period the amount of new tissue. Growth intensity, on the other hand, is constantly changing. It may vary from week to week, day to day, and even within one and the same day, as FRIEDRICH has pointed out (7). The amount of growth during a given period is then the sum of the prevailing growth intensities multiplied by the time each was in force. Let us take a specific example. Suppose a white pine first begins the formation of new xylem on May 1, and, on May 30, 60 new tracheids were in evidence in each tracheid row. It does not follow that 20 tracheids were formed the first 10 days, and 20 during each succeeding 10 days, making a total of 60. While the averdge growth intensity was two tracheids per day, the actual growth intensity may have vacillated on either side of this amount. It is obvious that it is quite impossible through comparative studies to obtain the prevailing growth intensity at a certain definite time. In order to do this the growth process would have to be actually observed. Some idea of the variability in growth intensity may be 214 BOTANICAL GAZETTE [MARCH gained, however, by comparing the average growth intensities for different periods in the growing season. It follows that the shorter the intervening time periods, the greater would be the vacillations in the data. With this idea in view table F was constructed. It includes figures of growth intensity from tree I during the summer of 1913. The width in microns of the new growth is given for 6 different periods, together with the total increase from period to period and the average gain per day. The last will give, not the actual, but the average intensity of growth of the period just preceding. If the data of April 26 and May 12 are compared, the following points are to be observed. The average growth intensity was greatest in cutting II, with cuttings I, ITI, and IV following in the order named. On June 12, 31 days later, cutting IV exhibited the greatest average growth intensity, with cuttings III, I, and I following in the order named. Again, in the cuttings of August 18 and September 19, different combinations occur. At the first named date, growth was more rapid in cutting II, while at the latter date it was in cutting IV. TABLE F GROWTH AMOUNT AND INTENSITY, TREE I; SEASON I913 Amount No. of . Gai A t No. of : Gai No. 26" 13 days Gain per'day seretg dave Gain per day Tees EIOLO Pls acacia [ace aad Ramiele SAS ae 716.36) 16 546.34] 34.16 Dix qarss 26.50. || seine torared|ang gahemchgalleotec acne 609.6 16 583.0 | 36.5 BY ween dicen TO6We - ladieedalawal sad lie sieotcte 472.4 16 305.7 22.9 Ae wine es Ox0) |lpaccaces|ssasnnndleneeeees 243.8 16 243.8 I5.2 . 6-12~'13 7737713 eog eG .Gs4 I164.2¢) 31 447.9K 14.4] 2176.0m) aT To1r.8p4| 48.2 Bh oiiiies 1021.1 31 411.5 13.3 | 1224.0 2z 202.9 9-7 Boa nace 1414.3 31 941.9 30.4 | 2067.2 2 652.9 31.9 ae 1251.2 31 1007.4 32.5 | 1219.2 21 | ln Guistcunkal ae gene 8-13-13 9-19-13, Laren 21760.0@) 41 0.04 0.04) 2176.0K| 37 0.0K 0.0K Deere gw siis 3100.8 4 1876.8 47.5 | 3394.6 37 293.8 7.94 Bea eoes 2448.0 4I 380.8 9.3 | 2339.2 BT le seestte cheshire oceans! Sesto Aeaaces 2007.2 41 848.0 20.7 | 2502.4 37 435.2 11.8 One space=1o days r915] BROWN—PINUS STROBUS 215 The results given in table F are represented in graph 1. The abscissas indicate the daily gain and the ordinates the time inter- vening in ro day periods. From the way in which the lines cross and recross, it is evident that average growth intensity and the actual amount of growth which is correlated with it vary between wide limits during different periods. The cambium may be very active for a time, then slacken in its growth, this to be followed again by renewed activity, with a final slump toward the end of 0 4 8 ae 4 20 Daily gain; one space=} GrapH 1.—Curves of growth intensity, tree I, 1913 the growing season. All the cuttings represent these two fluctua- tions except cutting III, and this departure may be accounted for through the inequalities of growth in closely neighboring parts. Two periodic optimums of growth intensity have already been noted by others. FRIEDRICH (7) made observations with the help of calipers, and found that in both coniferous and hardwood trees there were two periods of growth, one lasting until the end of May, then sinking some until the middle of June, followed later 216 BOTANICAL GAZETTE [MARCH by another maximum again in July, and then rapidly diminishing and ceasing altogether. Jost (13) has carried on observations which substantiate those of FRIEDRICH. It is remarkable how well the deductions of these two investigations are brought out in graph 1. The first optimum is without doubt made at the expense of the reserve food supply. It is not until June and even later that the bulk of the seasonal results of metabolism in the leaves is avail- able. This causes the second optimum, which may occur in July or August. It might be said in this connection that the amount of moisture and the prevailing temperature has been responsible for the results in table G. The meteorological data which follow TABLE G METEOROLOGICAL DATA, SEASON 1913 fas || imate) re a le ADTs iasisi'a dudes 48.1 1.49 Jule esac eteteces 7O.4 I.50 Main a cc ede etude 55-4 3.15 August.......... 69.6 1.92 JUNG is 26.47% adctalstana 65.0 2.00 September....... 61.0 3.28 are the best refutation of that argument. The decline occurred in three cuttings between the middle of May and the third of July, yet the temperatures prevailing were not such as to warrant this, nor was there a noticeable decline in the precipitation. My observations agree with those of FRIEDRICH, that there are in white pine at least two periods ofgmaximum growth. Irregularity of secondary growth in aerial parts A thorough treatment of the increase in growth in trees must necessarily be very comprehensive. The study in all its phases is a comparative one, for only by resorting to comparison can any fundamental rules of tree growth be formulated. A comprehensive study should therefore treat comparatively of the growth of (a) one individual during one growing season, (0) of one individual from season to season, (c) of different individuals in the same stand during one season, and finally (d) of different individuals not in the same stand. Data bearing on the first, second, and last phases of the 1915] BROWN—PINUS STROBUS 217 subject are available. For the third the reader is referred to the publications of WIELER (37-39), Jost (13-15), R. AND T. Harti (9-12), MiscHxKE (24), and others. The amount of seasonal growth in an individual or of growth up to a given point in the season is equal to the sum of the products of the different prevailing growth intensities by the time each was in operation. It follows that these summations would be quite different in different parts of the tree. The only reliable method to indicate the amount of seasonal growth at a given point and at a given time is as a percentage of the previous year’s ring. Even this is open to criticism, in that the annual increment often varies between wide limits from year to year. Yet general deductions may be drawn from data of this kind which will indicate to some extent at least the amount of growth at definite times. Table H was made with this idea in view. The figures were obtained from tree I. The width of the previous year’s ring represents the average of the last formed rings as exhibited in the 6 different cuttings.”° TABLE H AMOUNT OF GROWTH IN PERCENTAGE OF PREVIOUS YEAR’S RING, TREE I No. 4-26-13 | s-12—’13 | 6-12-"13 | 7-313. | 8-13-13 | 9-19-13 San Pane Bis hacia vee| 3.8 16.0 26.0 BB oiecvse a clhanaiian yee 4471.7 & LL. be gues 0.7 17.2 28.9 34.6 | 87.7 96.0 3535-3 DED Ss 2% ps 4.8 18.0 50.2 78.9 93-5 89.3 2619.4 ° EV is reson oe 0.0 11.8 60.4 58.8 09.7 |nsens Ses 2071.7 On April 26 the greatest proportion of new growth occurred in cutting III, with cuttings I, II, and IV following in the order named. On May 12 the order remained the same except that cuttings I and II had interchanged. On June 12 the ring was, theoretically at least, from one-fourth to ‘over one-half complete; on July 3 from one-third to over two-thirds complete; while on August 13 seasonal growth was over four-fifths complete in all cases. After the last named date, the growth was very sluggish 10 The last acts as a control and tends to eliminate error. ™ Growth ceased in cutting I after July 3, 1913; see table F. Diameter increase; one space= 230 # 218 BOTANICAL GAZETTE [MARCH for the next 37 days. Though still in evidence at the end of that time, we may infer that the ring was to all purposes complete. The contents of table H are presented in graph 2, where the abscissas represent the diameter increase of new growth and the ordinates 8 day periods. It is to be seen from both the table and the curves that in the long run the cambium in all parts of the tree tends to even up irregularities which arise from different growth intensities. If growth is sluggish at one place in the bole and rapid O 4 8 12 16 20 One space=8 days Grapu 2.—Curves of growth amount, tree I, 1913 in another during a given period, the pendulum of growth intensity swings to the other extreme in the next period and evens up the disparity. The irregularities of growth are manifested not only in the actual dimensions of the new formed tissues, but in the number of new xylem elements as well. If careful average counts of new formed tracheids are made, and these compared with the average number of tracheids at that point in the preceding ring, irregularities 1915] BROWN—PINUS STROBUS 219 crop out all along the bole of the tree. The data given in table I illustrate this very well. They were computed from tree III on June 17, 1913. This tree was a vigorous specimen on the north end of a small island in Fall Creek, east of Forest Home. The height was 81 feet, the diameter breast height 21.5 inches,’ and the age about 80 years. Exposure was to the southeast. Crown development was good but one-sided, and greatest to the southeast. Root development was also uneven, but the reverse of crown development, because the constant washing of the water and the mechanical action of ice had destroyed the root system on the east side. The tree was felled on June 17, 1913, and a double series of TABLE I EXTENT OF GROWTH IN TREE II, JUNE 17, 1913 N.W. sIwE S.E. SIDE Curmme | | «| PERCENTAGE | PERCENTAGE . | Tracheids in | Tracheids in Tracheids in | Tracheids in old ring new ring old ring new ring Mev dncnate meg cocnete 55-65. 20-25 0.38 55-65 20-25 0.38 Le Standart 32-34 15-18 0.52 30-35 I5-17 0.48 TED aid vnaas 22-24 Q-II 0.43 . 30 18-20 0.63 TV wes atx cas 23-25, 10-12 0.46 22 17 0.77 Wiss sao 16-18 6- 8 0.41 Ig-2I 13-15 0.70 MT soar e 16-18 6-7 0.35 23-25 I4-15 0.63 VEN oe bts 15-16 7-10 0.60 12-14 9-10 0.69 VIL. « eeccees 12-14 7-9 0.61 Q-12 6- 8 0.64 TX tae es 12-14 5-7 0.46 I2-14 7-9 0.62 9 cuttings taken at intervals of 10 feet, one on the northwest side and one on the southeast side (exposed). Careful average counts were then made of the number of new formed tracheids, as well as those in the preceding ring at each point. On June 17, 1913, growth was more advanced in every cutting on the southeast side, the first two cuttings excepted, than on the northwest side. This was to be expected, because of direct insolation and larger crown to the southeast. But in both series of cuttings marked vacillations in growth are evident, so that it follows that growth irregularities express themselves not only in a variability in thickness of tissue, but also in the number of elements laid down. 2 Exceptionally high because of the buttressed base. 220 BOTANICAL GAZETTE [MARCH Growth irregularities in individuals have been noted by others, although their results are in some cases to be questioned because they were based on external measurements alone. Such are those of Curistison (5), Von Mout (25), and Josr (13), reference to whose work has already been made. The results of TH. HaRtTIc (12) and Rozsr. Hartic (10) can have no significance in this con- nection, inasmuch as individuals were felled to secure data and consecutive measurements were quite impossible. MuscHKE (24), as already noted, employed an increment borer, and his results, with those of WIELER (39) who pursued the same method, are more reliable though not as accurate as is desirable. The former made comparative notes on Norway spruce and Scotch pine, and his results clearly indicate growth fluctuations. WIELER subjected TABLE J GROWTH OF WHITE PINE AT DRESDEN, GERMANY I II III Date 1894 bs Ring breadth No. of Ring breadth No. of Ring breadth No. of mm. tracheids mm. tracheids mm. tracheids April 24. | cetiareatelewsewe ties leeeeatatenellesess pede ‘ 0.48 13-14 May GF lhe gunn oudoae sia Coane Oo Deve leicceernn AoE kale Ae I.12 26 May 16 0.08 3-4 0.14 8-10 2.34 47 May 26 Lost SEVELAL liscscce sine ccualtoncie saan 2.00 47-50 June 5 O.1I 3- 4 |0.18-0.20 4-6 4.12 89 June 16 0.06 2- 4 0.12 6-9 3-15 72 June 26 0.15 6- 8 0.16 6-8 2.74 73° July 7 0.19 8-9 0.46 15 5.61 113 July: 17 0.45 I5-17 0.47 13-16 6.67 150 July 28 0.23 8-11 0.53 20-23 9.23 175 August q7 0.42 17-18" 0.32 15 6.25 150 August 18 0.34 12-18 0.31 14 5.68 135 August 28 ].......... 15-20 0.30 13-15 5.22 IIQ September 8 0.26 TI-13 0.55 23 9.32 218 October 17 0.38 13-19 0.38 TO. Wesehitepsascauadalte Symeranneuedee November 1 0.26 II-13 0.49 20-22 9.26 212 more trees to the same inquiry, and his investigations are of greater interest because he worked on white pine. Table J indicates his results on the three different specimens mentioned previously; and in each case fluctuations in growth are marked. The work of BUCKHOUT (2) serves to accentuate the same point. He made bark measurements on a white pine and a larch which extended over a rgt5] BROWN—PINUS STROBUS 221 period of 4 years. The results were plotted in curves where the abscissas represented 5 day periods and the ordinates increase in circumference in sixteenths of an inch. In each of the four curves for white pine, from several to many growth fluctuations are evident. Still other researches could be cited to emphasize the same point. Many irregularities in growth occur during the season of cambial activity. Comparative growth studies between different individuals of white pine (not in the same stand) were also carried on during the summer of 1913. In such investigations only temporary mounts were made and the necessary data secured from these. A few extracts from this part of the work follow. On May to two cuttings were made at the base of the “Wolf” tree previously described, one on the north side and one on the south side. The first exhibited about ro tracheids (7 complete) as to size on this date, while 12-14 tracheids were in evidence on the south side. On May g two cuttings were secured from a large white pine which presented different conditions of site, although in the same vicinity. This was a mature specimen some 110 feet high and 22 inches diameter breast height. It stood in a mixed hardwood stand where the land sloped sharply to the south. Ground cover was sparse. The tree, while mature, appeared to be still in vigorous growth. The north cutting (next to the bank) exhibited 2 tracheids, neither complete as to size; while in the south cutting no new tracheids were to be seen. Without doubt growth. was going on vigorously in the upper part of the tree at this date. Observations on the same tree at a later date showed similar discrepancies. On June 13 the south basal cutting of the “Wolf” tree showed 20-25 tracheids already formed; 15 or 16 of these had apparently attained their ultimate size. The same cutting from the older specimen at that date possessed 11-13 new tracheids, 7-9 of which had attained approximately their maximum size. The amount: of growth was decidedly less in the older individual. Even wider discrepancies may be expected than the above where the differences in age are greater. For example, a young tree was examined on the same date (June 13). This was a thrifty 222 BOTANICAL GAZETTE [MARCH 14 year old individual situated in the midst of the stand and only a few feet from the “Wolf” tree. In fact, the “Wolf” tree may have been one of the seed trees from which the stand had arisen. The cutting: was made at approximately breast height, and already on June 13 the annual ring exhibited some go new tracheids. Three weeks later summer wood formation began. It follows that up to July 1, at least, we may expect many discrepancies in growth to occur. The greater the difference in vigor between the two trees compared, the greater will be the difference in the amount of growth at that period. Others have noted the same growth irregularities between different individuals of the same species. Among these is Rost. Hartic (10), who expresses himself emphatically on this point. I quote from his text as follows: Bei freiem Stande und directer Insolation des Baumes, besonders aber des unbedeckten Bodens beginnt der Zuwachs in den unteren Stammtheilen weit friiher, als im geschlossenen Bestande und bei einem Boden, der entweder beschattet (Nadelholzstand) oder von einer dichten Humusdecke bekleidet ist. An 100 jaihrigen Fichten, welche isolirt an einem Siidhange standen, war schon am i. Mai auf Brusthéhe der Dickenzuwachs in Thiatigkeit, an ebenfalls frei stehenden gleich starken Baumen des Nordhanges auf nasskaltem Boden war am 26. Mai noch kein Zuwachs bemerkbar. Im vollen Waldesschlusse zeigten manche Fichten und Kiefern selbst am 1. Juni noch ruhendes Cambium auf Brusthohe, u.s.w. An excellent illustration is likewise afforded by WIELER’s table (table I). Trees I and II were in a 4o year stand, where they had been subjected to similar silvicultural conditions. WIELER failed to say whether tree II was bored on the north or south side, but in either case the tracheid numbers are seen to be quite different from those in tree I. Growth curves from neighboring trees under similar conditions never coincide. Fluctuations are constantly arising which upset the regularity of growth and for which no one factor is responsible. Termination of secondary growth in aerial growth The autumn condition of the cambium was observed in tree I both in 1912 and 1913, inasmuch as cuttings first began on this tree on August 5, 1912. The data given in table K include the 1915] BROWN—PINUS STROBUS 223 results obtained from two cuttings in 1912 and the last two cuttings of 1913. The table is of value because it offers comparative data which are strongly correlated with the results of others. While the periods of time between the cuttings of 1912 and 1913 are different, it is obvious that in each year the greatest increase of xylem toward the end of the growing season was in the basal cutting. In other words, growth continued vigorously at the base of the shaft until well into September, while in the higher parts it had either TABLE K TERMINATION OF GROWTH, TREE I; 1912 AND 1913 WIDTH OF RING PERCENTAGE Cormic Avount oF |BELCENTACE | No, or pays |" oF bauby Aug. 5, 1912 |Sept. 26, r912 Mes aetenge ..-| 2643.8@] 3176.9mM] 533.16 20 52 0.38 Thats .6 aden 304074 IAcascewse afer ss Gowen lowkpaad eee SO ieretsnshsedi asta DD a ss seats 2529.6 2622.1 92.5 3.6 52 0.07 Was ecce tie en 1550.4 2328.3 777-9 50 52 0.96 Aug. 13, 1913/Sept. 13, 1913 Teneeewa ane 2176200 | 2776.01 lesa ssveess|saeauacirs Bt Wet ee eke Le oeka gue 3100.8 3394.6 293.8 9-5 31 0.31 TT. ee heoane 2448.0 DEGO se Nei cospeiace at Socllic peer enact BL |aainasdtic RV i352 ediees ses 2067.2 2502.4 435.2 21.1 31 i 0.68 totally ceased, as in cutting I, 1913, or continued very sluggishly, and this condition was exhibited by tree I during two successive years. It follows from the preceding paragraph that in normal white pine trees growth is apparently first retarded above, retaining its vigor longest in the basal portions of the bole. The results of others on coniferous species lead to the same general conclusion. T. Hartic (12) worked on both hard and soft wood trees and came to 33 The disparity in the data of cutting I for the two consecutive years may be questioned. In 1912 there was an apparent gain of 20 per cent during the period intervening between the two dates given, while in 1913 no growth was evident at all after the first date. But in 1912, the first cutting was made on August 5, while the following year it was 8 days later. This probably accounts for the increase in the first case. Growth was still in evidence there on August 5, but had the cutting been made 8 days later, the results might have been decidedly different. 224 BOTANICAL GAZETTE [MARCH the conclusion that cessation of growth occurred later below and last of all in underground parts. R. Hartic (11), following up these studies, made cuttings from species of Pinus, Picea, Larix, and Abies, in order to determine the condition of the cambium in different parts of the shaft. Cambial activity in each case was farther advanced above than below. It gradually diminished in intensity during the months of May,, June, and July in the higher parts, while below the same applied to the months of June, July, and August. Kwnupson’s data (16) indicate the same condition of the tissue for Larix laricina, except that in the larch the phenom- enon occurred in July instead of August and September. The disparity in growth in different parts of a tree is without doubt dependent on conditions of temperature. The primary cortex persists in white pine for a long period, in some cases as long as 50 years. ‘This condition is brought about through the division of the original cells of the cortex by anticlinal walls, and the sub- sequent enlargement of the two cells thus resulting. Meanwhile, cork formation remains superficial, so that the upper portions of the tree, even where the bole is 15 inches in diameter, are clothed by a layer of living, chlorophyll-bearing, primary cortex. Sooner or later, however, and varying markedly in different individuals, deep cork formation begins. This is evident first through the formation of isolated areas of brown tissue which stand out sharply from the surrounding living cortex. These increase in number, finally become confluent, and the characteristic old bark of white pine is formed. With thisechange in the type of cork formation there is correlated a modification of at least one factor potent in forwarding growth. The first phellogen is continuous around the whole circumference and functions until deep cork formation begins. New cork cells are added to the outside, and with the increase in circumference the older ones on the extreme outside slough off. So long as the primary cortex persists, the corky mantle remains thin and its protective value is in like proportion restricted. With deep cork formation, however, the conditions are altered to a large extent because the corky layers which are then formed through the activity of each phellogen accumulate. Protection of the cambium in the basal portions of the tree is thus greatly increased. 1915] BROWN—PINUS STROBUS 225 Changes in temperature are less effective there because the thick corky layers tend to equalize the conditions which prevail at different times during the growing season. Cool autumn nights, for example, would chill the cambium in the upper parts of the tree much earlier than below. Temperature changes become operative first where the primary cortex still persists, that is, where the bark is yet smooth. This without doubt explains the disparity of growth as we find it in white pine. Growth is first retarded above, but may go on vigorously below for a much longer period. The exact time of growth cessation apparently varies widely in different species, in different localities, and in different sites. While wide variations occur, still certain generalizations apply. At the outset the term ‘“‘growth” is a misnomer. As already noted, phloem formation, at least in conifers, does not cease with xylem formation, but continues uninterruptedly until late in the fall. It is necessary, therefore, to discuss xylem and phloem separately in their relation to cessation of growth. A comparison of cuttings from tree I for the years 1912 and 1913 will give an idea of the seasonal termination of xylem formation. One discrepancy was noted at the start. In spite of the fact that the final cuttings in 1912 were a week later than those in the follow- ing year, growth was apparently more vigorous at the later date in 1912 in all four cuttings. This is to be explained in two ways. It was due either to seasonal variations or to the fact that the vigor of the tree had been materially lessened the second year through the many cuttings taken from it. An examination of the meteora- logical data for the two seasons has added no convincing evidence, inasmuch as comparative figures of growth for the two years were not at hand for a sufficiently large number of individuals, and general assumptions were therefore out of the question. Possibly both factors were in force. To give the exact time or a definite place in the tree for the termination of xylem formation is quite impossible, as the data on tree I indicate (table F). In 1912 growth was still in evidence on September 26 in all four cuttings, as transitional forms of tracheids could be noted in every case (fig. 6). Growth, however, was going on at this date very sluggishly. Often only one flattened transitional 226 BOTANICAL GAZETTE [MARCH tracheid occurred between a cambial cell and a fully formed (as to size) tracheid, and occasionally here and there in a cutting this was lacking entirely. Again, in the cuttings of September 19 of the following year the same condition of affairs existed. While growth as to relative amount had to all purposes ceased, still all indications pointed to the fact that in all four cuttings it was going on, though very slowly. In both cases growth appeared to be most sluggish in cutting III, but no reason can be assigned to account for this fact. The data from the preceding paragraph lead to the following conclusions. Xylem formation in tree I continued during two successive years until the last half of September, possibly even as late as October 1. Further, it was in evidence throughout a large part of the bole, as cutting I was 38 feet above the ground and the terminal leader extended only 17 feet beyond. Whether it still continued in the terminal leader cannot be concluded from the present investigation. If we correlate these deductions with those previously reached in the paper, the following points are evident: (a) growth intensity falls off first in the upper parts of normal white pine trees, more tardily below; (}) cessation of xylem formation does not follow the same law, but persists sluggishly in all parts of the bole (with the possible exception of the terminal leader) until the latter part of September; (c) the exact time of the end of xylem formation was not determined in the present investigation, but it is safe to conclude that it was practically complete by October 1. ‘ The results of the present study are contrary to those of Rost. Hartic (9), who says, “Der Abschluss der Zuwachsthatigkeiter- folgt oben entsprechend friiher, als unten.” Too much emphasis must not be placed upon this statement, because (1) Hartic made external measurements only, and (2) his results may have been influenced by subsequent phloem formation after xylem formation had ceased. Roxst. Harric avoids the issue in part when he states that cambial activity occurs in the tops of trees in Pinus silvestris, Picea excelsa, and Larix decidua during the months of May, June, and July, and at the base during June, July, and August. While he implies also a cessation of growth, he does not say it in so many \ 1915] BROWN—PINUS STROBUS 227 words. WIELER (39) has given some data concerning the termina- tion of growth from the three white pines which he investigated (table J). In tree I the ring was complete on the north and south sides at the base on September 8. In tree II it was complete on the south side at the same height on August 28, while in tree III it was still in progress on September 8. In general his results indicate that in the vicinity of Dresden, Germany, growth in white pine ceases slightly earlier than at Ithaca, N.Y., a reasonable conclusion, since the former is in a higher latitude. The work of BuckHout (2), already cited, is of interest in this connection. While his measurements were made externally and are therefore subject to the same criticisms as those of TH. HarTIc, certain facts are obvious. During the four years over which his experiments extended, growth was manifest in the white pine during the last ro days in August and in two as late as September 8. His results serve to accentuate the fact that white pine has a long growing season, much longer than the European larch, with which he also worked. The growing season of tree I may be used, in spite of variations which occur between individuals in that respect, as a general indi- cator of white pine growth in the vicinity of Ithaca. As already indicated, growth in white pine may be divided into two periods: (A) growth without cell division and (B) growth with cell division. B of necessity follows A. Considering A and B together, growth began in tree I before March 29, 1913, and continued until after September 19 of the same year, a period of over 5.5 months; and this does not include the late phloem development which without doubt continued into October. Cell division began before April 26 of the year in question, and if growth is considered in the narrow sense, the period is shorter by several weeks. If there are any grounds for the statement that trees complete their seasonal growth in a period of 4 or 5 weeks, white pine is an exception to the rule, as here the growing season extends over a period of 4-5 months, depending on the interpretation of the term “growth.” Differentiation in the annual ring in aerial parts In working up the foregoing data, no stress has been laid on differentiation within one and the same annual ring. As is generally 228 BOTANICAL GAZETTE {MARCH known, each normal ring may be divided into spring wood and summer wood, or better early wood and late wood. The second of these two regions is distinguished from the first either by a diminution in the size of the vessels, as in the case of ring porous woods, or through a reduction in size and flattening of the elements formed in the outer part of the ring. The proportion of early and late wood in the ring affects strongly the physical properties of the wood, and as a result the early workers gave much time to its con- sideration. The factors controlling the amount as well as the time of late wood formation have been a subject of inquiry, and a hasty review of the literature on the subject, as well as a summary treatment of the results of this study from this viewpoint, are appropriate here. One of the first theories offered to account for the variation in ring was that of Kraus (19), SACHS (30), and DeVries (36), who explained it through differences in bark pressure at different times during the growing season. The radial pressure was at a minimum in the spring, permitting a greater expansion of the new elements, while it gradually increased during the growing season, ending with a maximum. The pressure leading up to the last was responsible for late wood formation. This theory was disproved by KrapseE (17, 18) beyond all contention in 1882, and since that time a number of new theories have sprung into existence, each with adherents. Rost. Hartic (g) sought to explain the late wood formation in that the cambium was but,poorly nourished in the spring. Late wood formation depended upon improvement in the nutritive conditions later in the season. According to Hartic the size of the lumina of tracheids is dependent on the amount of transpiration of the foliage, while the thickening of cell walls is correlated with the increased amounts of food available at that time of the year. Diametrically opposed to Hartic’s theory is that of WIELER (37) and Russow (29), which was based on the assumption that the early wood owed its origin to better conditions of nourishment. STRASBURGER (32) accepts neither of these theories, but explains annual ring formation as.a normal fixed process. The young wood is the response, according to his theory, on the part of the plant 1915] BROWN—PINUS STROBUS 229 to a demand for conducting tissue, while the late wood is formed to increase the stability of the tree. The last factor may have been in force from the beginning, but was at the start overshadowed by the first. Mer’s theory (23) rests firmly on the general assumption of WIELER as given above. According to his idea, the early wood results when the cambial activity is at a maximum, that is, in the spring, while late wood formation occurs when growth is going on very sluggishly, as in August and September in the white pine. The last elements of the annual ring are flattened because with the falling off of growth intensity the radial stretching of the young elements subsides in the same proportion. Still another theory is of interest here because it departs decidedly from all of those mentioned. ScHwarz (31) assigns the chief réle in late wood formation to longitudinal pressure. This is in force throughout the growing season, but its effects are lost at first as the result of other factors, such as nourishment, which are temporarily more potent at that time. With a decline in the action of these, the effect of longitudinal pressure (gravity) reasserts itself. No attempt has been made in the present work to refute or substantiate any of the theories above mentioned, nor in fact to bring forward a new hypothesis for annual ring formation. Other workers of the last decade have given the matter serious thought, but the problem still remains unsolved. It is the opinion of the author that several factors are potential, but inasmuch as these cannot be controlled by the investigator, the precise influence of each on growth cannot be definitely determined. The results obtained appear to substantiate Mrr’s theory to some extent, in that growth in tree I was more rapid in the spring and early summer than subsequently. But the assumption that the cambium was better nourished at the beginning of growth than later is not justi- fied from the present inquiry. It can only be said, in conclusion, that late wood formation occurs at a time when growth is proceed- ing very slowly. No definite results were obtained concerning the time that late wood formation begins. White pine does not lend itself to a study 230 BOTANICAL GAZETTE [MARCH of this sort, because the transition from early to late wood is always very gradual, and it is difficult to distinguish the first formation of late wood tracheids. Larch should prove much more satis- factory for this study. But in spite of the difficulties mentioned above, it was obvious that late wood formation was in evidence in tree I on August 5, 1912, and on August 13 of the following year. On each of these dates all four cuttings showed some traces of it, and, further, it appeared to be slightly more advanced in cuttings I and II than in the ones taken lower on the bole. This was to be expected from what has been previously said; late wood forma- tion begins first in the upper portions of the bole. Primary growth in aerial parts Some attempt was made in the investigations to secure reliable data concerning the elongation of aerial parts. A sample plot of 0.05 acre was laid off on May 3, 1913, in the vigorous young white pine stand mentioned previously. It included 115 trees which ranged from 4 to 11 years. The soil was of medium thickness, underlaid by sandstone and shale; exposure was open. All the trees were seemingly vigorous. The trees were first examined on May 3 as to elongation of aerial parts. At that date elongation had already begun in all the trees on the plot, which varied from 0.5 to 2.5 inches. Greatest elongation had occurred in the terminal leader, while it was less pronounced in the slower growing lateral branches. The leaf fascicles were in evidence, hut had as yet attained no appreciable length. Observations corresponding to the above were subsequently made on May 30, June 17, and July 4 of the same season. Accurate measurements of the terminal leader and of the preceding year’s growth for 50 trees were made in each case and the results collected in table L. The average growth of the preceding season is con- sidered as the mean of the average preceding year’s growth as found on May 30, June 17, and July 4. It is to be observed that the last vary slightly, as no attempt was made to select the same 50 trees on each date. The measurements are given in inches and fractions of inches. rors}. BROWN—PINUS STROBUS 231 Elongation of aerial parts began in the young growth in question before May 3 and continued until about July 4. Assuming that growth before May 3 proceeded at the same rate as between May 3 and May 30 (1.2 per cent a day), we can only infer that the awaken- ing of growth in length in the shoots began about 8 days before (April 25), a conclusion that field observation fully confirmed. Cessation of growth in length in shoots had occurred by July 4, without doubt because at this date the length of the season’s growth had surpassed that of the preceding year, and furthermore the terminal cluster of buds was fully formed. It follows from the data that in 50 young trees in 1913 elongation of the terminal shoots TABLE L GROWTH IN LENGTH IN THE TERMINAL LEADER Avera; Mean Per cent of Date pe growth of growth of preceding | No. of |Per cent) Ber cane cea) PemeeE | pemsaaing, | “seamen [ee on aaa 53- 3-I913.... E25) Weavsaen gen 13.55 a8 Vnwicewiboes anna aceane-d 5-30-1913.... 5.6 13.98 13.55 41.3 27 | 32:0 | 1.2 6-17-1913....| 10.02 13.22 13.55 73-9 18 | 32.6 1.8 7- 4-1913...-| 14.37 13.45 1355 106.1 17, | 32.2 I.9 began in the last part of April and continued until July 4. What applies to the terminal shoot is even more applicable to the lateral branches where long growth is not as vigorous. Furthermore, the same relation exists between young and old trees. In the latter growth in length must have been completed by July 4, so that it may be concluded that in white pines in the vicinity of Ithaca, growth ceases during the early part of July." Before proceeding to a review of the results of others, perhaps a brief discussion of the elongation of the leaf is appropriate here. Only one observation was made in regard to this point, but for- tunately the date was July 4, so that it offers a chance for com- parison between growth of shoots and leaves. The leaves on the 4 MEISSNER (22) has noted the formation of the so-called ‘‘Johannistriebe” in rare cases in white pine. Bud formation occurs in the normal way, but in such cases some buds continue growth the same year. This peculiarity has been noted in many dicotyledonous fruit trees, but is rare in conifers. 232 BOTANICAL GAZETTE [MARCH terminal shoot of the season were compared with those of the pre- ceding season as to length (not thickness), and the results tabulated in table M in inches. Only 6 trees were examined, so that we can- not expect the uniformity that more extended observations would offer; still, the results are of value in that they lead to a general conclusion. TABLE M TABLE OF LONG GROWTH IN NEEDLES NEEDLE LENGTH A DaTE DIFFERENCE ae sane Old New PERCENTAGE 7-4-1913.... 3-75 2.38 137 63 63 7-4-1913.... 2.75 1.75 100 63 63 7-4-1913.... 2.88 2.00 88 69 63 7-4-1913.... 2.88 2.13 75 73 63 7-4-I913.... 2.75 Teh 62 4I 63 7-4-1913.... 2.38 1.75 63 73 63 Elongation in the needles had not ceased on July 4; in no case was it three-fourths completed, as a reference to the table will show. Assuming that elongation in the needle is contemporaneous with elongation in the shoots,’s that is, that it began on April 26, it follows that during a period of 69 days the needles had attained on an average 63 per cent of the average growth of the preceding season. Assuming again that the rate of elongation was the same during the rest of the season, we may compute roughly the period necessary for the needles to complete their growth, that is, growth in length in the needles would be completed about 4o days after July 4, that is on August 13. It is reasonable to assume from the data on the 6 trees that the elongation of white pine needles ceases somewhere about the middle of August. If we correlate the results given above with those which have been previously given, we arrive at the following interesting conclusions for white pine in the vicinity of Ithaca. Growth in thickness (secondary thickening) begins in white pine before the elongation of aerial parts, either of shoots or needles. Elongation of shoots and needles begins simultaneously. The elongation of 15 Field observation substantiatéd this assertion. 1915] BROWN—PINUS STROBUS 233 the shoots ceases during early July, while that of the needles continues well into August. Comparative studies of the growth in length of shoots and needles have been made by others. WrELER (39) found, for example, that in the needles growth was completed in Pinus mon- tana at the beginning of July, in Pinus austriaca at the end of August, in Pinus silvestris by the end of July and the beginning of August, in Pinus Strobus during the course of August. Growth of the needles in Pinus, according to his observations, varies with the species. MEISSNER (22) likewise noted that growth of needles of a number of species of pine varied, especially that of Pinus silvestris. While he gives no exact date for the termination of growth of needles in the species, he states that growth in length of the terminal shoot ceased about the middle of July, and in all cases the growth of the needles continued later than that of the shoot. Whether all species of Pinus agree in this respect remains yet to be determined; white pine has proved no exception to the rule. Primary growth in underground parts The detection of primary growth in underground parts is in some species attended with obstacles which are well nigh insur- mountable. Often the new tissues are little or not at all differ- entiated from those of the preceding year, and in such cases it is very difficult to detect the beginning of growth in length in the spring. This is the case in white ash, where little coloration results, so that it is quite impossible to separate new and old parts of the root. Fortunately, in the Coniferae this does not apply, for within a space of 1 cm. marked brown coloration appears, so that new growth can be detected without any difficulty. Furthermore, after the cessation of growth in the autumn, this brown mantle approaches nearer the root tip, so near in fact that one can be reasonably sure as to the presence of new growth. The first observations on root growth were made on April 26, 1913. Roots were obtained from 3 and 4 year white pine specimens in the nursery. The frost had been out of the upper soil layers for only a short time, yet evidences of growth were to be seen in many of the root tips in the shape of small white translucent 234 BOTANICAL GAZETTE [MARCH protuberences 1 mm. or so in length. Very little elongation had occurred, but clear evidences of its inception were to be seen. Growth in length had already begun. This early study, as well as the subsequent ones, also brought out another interesting point in regard to white pine roots, namely that there are two kinds of roots underground, just as there are two kinds of branches above. This is well brought out in fig. 11, where long roots and short roots are plainly visible. The short roots occur irregularly on the sides of the long roots, either singly or in tufts of varying size. Where the latter occur, they arise through the forking of a normal short root; this is repeated a number of times and each branch remains short and acquires a growing point of its own. Occasionally one of the apices in the tuft grows out into a long root, but the majority of them remain short, function for a time, but eventually die and disappear as the diameter of the long root increases. Other workers have already noted the same condition in white pine roots. BiisGEN (4) has described it in some detail, and adds further that mycorhiza are found in the long roots, while they are entirely lacking in the short roots. Data bearing on root growth were next obtained on May 10. Roots were taken from a thrifty young pine about 12 years old, which from its position on the north bank of Fall Creek near Varna, N.Y., was admirably fitted for the purpose in hand. The creek had partially undermined the sandy bank, and root apices were readily obtained by digging back into the bank. Some of these are repre- sented in fig. 12. The new growth had already attained a length of two inches in many cases, and, as seen in the figure, was sharply marked off from that of the preceding year. This is due to the fact that in the last cork formation (as well as secondary thicken- ing) had occurred, and the thick primary cortex which forms the bulk of the thickness in the new growth was entirely lacking. Browning of the tissues, a peculiarity already described, had also started in the new growth, as the root tip at the extreme right bears evidence. Lateral roots in the form of translucent dots were just appearing on the sides of the growth of the preceding season. It was quite impossible on May 10 to make comparative notes of root growth in 1912 and 1913, inasmuch as the point of origin of growth in the spring of 1912 was not evident. All trace 1915] BROWN—PINUS STROBUS 235 of yearly elongation is lost after the first year. No attempt was made to trace rapidity of growth of white pine roots. Roots from the same tree on May 30 exhibited an average growth of 4-5 inches, but no other material was secured. We can only infer from the data at hand that growth in length began as early as April 26, possibly much earlier. The results of others in regard to the duration of root growth are interesting in this connection. ReEsA (27), after repeated observations on root growth, came to the conclusion that there are in all roots two periods of root development, one in the spring, which occurs mainly before the unfolding of the leaves, and a second during September and October. The last persisted through the winter in dicotyledons, with many interruptions from time to time, but without complete cessation. In conifers, on the other hand, there was a decided rest period during January and February. WIELER (38) combated Resa’s conclusions and maintained that in the autumn, after leaf fall and the resulting lessened demand for water, no new roots were necessary. PETERSON (26) worked with young and old trees of a number of dicotyledons, as well as specimens of Picea excelsa, Pinus montana, and Larix decidua. His results in every way substantiate those of Resa and contra- dict the conclusions of WIELER. Among other points explained, PETERSON points out that there is a period of root elongation which may occur in the spring anywhere between February and June. In June, and especially in July, elongation gradually ceases. This is followed by a reawakening in growth in length from August until October and even into November. The author does not state in which period growth is more intense. The researches of BiscEN in roor (4) and ENGLER in 1913 (6) substantiate in every way those of Resa and PETERSON, so it may be concluded that there are two periods of elongation, and furthermore, that in white pine the first begins in late April and continues into early June or even later. Secondary growth in underground parts Secondary growth in roots, as in stems, begins the first season, and once started proceeds in the usual way. Mention has already been made of the variability in white pine roots as regards the 236 BOTANICAL GAZETTE [MARCH number of xylem rays. The secondary xylem forms between the primary xylem rays and under the primary phloem, and it follows that there are as many secondary xylem areas as there are primary xylem rays. In a young root where the secondary thickening has begun we find the primary and secondary xylem areas alternating with each other (figs. 9 and 10). It is usually not until the following year that the segments unite and complete the ring of cambium. An unsuccessful attempt was made to find out at just what period in the growing season secondary thickening began in the root. Roots were examined on May 11 and again on May 30 with this object in view. No secondary growth was in evidence in either case in the new tissues, even when, as at the last date, elongation had gone on to the extent of 5-6 inches. In every case, however, where the last formed growth of the preceding season was examined, secondary xylem was in evidence between the poles of the primary xylem, and evidence of a resting period was to be seen, so that it must be concluded that secondary growth occurs later in the growing season than May 30, probably during the second period of activity in the autumn. The cambial segments, however, apparently do not unite over the poles the first year, so that second- ary growth the first season is confined to as many separate areas as there are poles. The course of secondary thickening in the root, once started, is much more irregular than in the aerial parts. The annual rings are usually thickest on the lqwer side of the roots as they enter the root crown, but all regularity is lost a short distance from the bole. The rings may be narrow here and broad there, and apparently their position in the ground has no appreciable effect; geotropism is not a factor in annual ring formation. False and double annual rings are often present. As RUBNER (28) has pointed out, the cambium may be active on one side of a root and dormant on the other for several years without its vitality being impaired, and this is responsible, in part at least, for the irregularities in growth which arise. Furthermore, the tissues of exposed roots present the same characteristics as those in aerial parts, a peculiarity previously noted by Kny (20). In conclusion, it may be said that roots, 1915] BROWN—PINUS STROBUS © 237 while conservative structures in many respects, exhibit much more irregularity in annual ring formation than do stems. Summary 1. The winter condition of the secondary cortex and cambium of white pine is similar to that of Pinus rigida. The marked differ- ences which occur between the mature bark of white pine and pitch pine are occasioned by changes which take place in the outer cortex (periderm). 2. The cambium varies both in number of cell layers (2-10) and _ thickness in different parts of a tree. It is smallest in both these respects in the twigs and young branches, and increases gradually in dimensions from the apex downward, until that point is reached in the bole where the last annual ring is the thickest. Thereafter, the decrease in the diameter is not proportional to the falling off in the diameter of the last formed ring. 3. Phloem development continues until late in the autumn, much longer than xylem development. Sieve tubes in all stages of formation occur between cambium and fully formed phloem. The seasonal growth of phloem exhibits little or no compression as late as October first. Subsequently contraction occurs, due to the extreme cold temperatures of winter. All the seasonal growth of phloem is crushed with the exception of the last 6 or 8 transitional tracheids. Compression is greater in the crown than below. 4. The processes of primary thickening and secondary thicken- ing overlap, and both may be going on in closely neighboring spots in the tree at the same time. 5. Growth in white pine is divisible into (2) growth without cell division and (0) growth with cell division. The first begins as early as March and the elements concerned (phloem) increase in radial diameter from 50 to over 100 per cent. The awakening of growth is due apparently to the rise of soil water with an accom- panying increase in temperature. 6. Growth by cell division begins during the last half of April. At the start it is very rapid, and more elements are formed at the inside of the cambium than at the outside. The formation of 238 BOTANICAL GAZETTE [MARCH new xylem elements follows the same order as in pitch pine, that is, it begins first in the bole at some distance below the apical shoot and spreads upward and downward. As a result, growth at the base of a tree may begin several weeks later than in the crown. 7. The awakening and rapidity of growth is dependent on three factors, moisture, available food (reserve), and temperature. The first two are at an optimum in the spring; the amount of growth therefore is directly proportional to prevailing temperatures. 8. The intensity of growth is a variable factor which changes from day to day and even within a single day. Two periodic optimums of growth intensity occur, one during May and early June, the second in July and August. These vary from time to time at a given height in the tree and follow no definite law. 9. The amount of growth at a definite time and place in the tree is equal to the sum of the prevailing growth intensities by the time each was in force. It is very irregular at different heights in the tree, but the cambium tends to even up discrepancies as the season progresses. The irregularities of growth are manifested not only in the actual dimensions of the newly formed tissues, but also in the xylem elements. Wide discrepancies may occur in closely neighboring trees; in general, larger differences may be expected the greater the disparity in age. 1o. Growth is first retarded in the upper portions of the tree; it may continue vigorously below for some weeks longer. 11. Xylem formation goes on very sluggishly in all parts of the tree (the terminal, leader excepted) until late September and early October, phloem development as long as temperature permits. 12. The total growth of white pine extends over a period of 5.5 months, growth by cell division between 4 and 5 months. 13. Late wood formation begins during the first half of August; it is associated with a decrease in growth intensity and begins first in the higher parts of the tree. 14. Elongation of new shoots and leaves is simultaneous and begins in early May; it manifests itself only after xylem formation has begun. Growth in length in the shoots ceases about July 1; needle growth may continue until August 15 or even later. t915] BROWN—PINUS STROBUS 239 15. White pine has long roots and short roots. Only the first elongate to any extent and often are in symbiosis with mycorhiza. Growth in length begins during the last half of April, in some cases even earlier; no reliable data were obtained regarding its cessation. Secondary growth occurs during the first season and proceeds in the usual way. This work was undertaken at the suggestion of Professor W. W. ROWLEE, Cornell University, to whom I am very grateful for help and criticism. Acknowledgments are also due to Professor WALTER Mutrorp and Professor JoHN R. BENTLEY of the De- partment of Forestry, New York State College of Agriculture, Ithaca, N.Y. SyRACUSE UNIVERSITY SYRACUSE, N.Y. LITERATURE CITED 1. Brown, H. P., Growth studies in forest trees, I. Pinus rigida Mill. Bot. GAz. 54:386-402. 1912. 2. Bucxnout, W. A., The formation of the annual ring of wood in the Euro- pean larch and the white pine. Forest Quar. 5:259-267. 1907. 3. Biiscen, M., Bau und Leben unserer Wdldbaume. 1897. , Einiges iiber Gestalt und Wachstumweise der Baumwurzeln Allg. Forst- und Jagd-Zeit. 77:273-278, 73:305-309. IgoI. 5. CHRISTISON, H., Observations on the annual increase in girth of trees in the Royal Botanic Garden and at Craighill, near Edinburgh, from 1878 to 1887. Trans. and Proc. Bot. Soc., Part I, July 12, 1887; Part II, Feb. 14, 1889. 6. ENGLER, A., Perioden in Wurzelwachstum. Promethes 16:623, 624. 1905. 7. FRIEDRICH, J., Uber den Einfluse der Witterung auf den Baumzuwachs. Mitth. Forstl. Versuchs. Oesterr. 22:pp. 160. 1897. 8. Gorr, E. S., The resumption of root growth in spring. Wis. Agric. Sta. Ann. Rep. 15:220~-228. 1898. 9. Hartic, R., Das Holz der Deutschen Nadelwaldbéume. 1885. p. 35. 10. , Ein Ringelungsversuch. Allg. Forst- und Jagd-Zeit. 1889. II. , Anatomie und Physiologie der Pflanzen. 1891. 12. Hartic, T., Anatomie und Physiologie der Holzpflanzen. 1878. 13. Jost, L., Betrachtungen iiber den zeitlichen Verlauf des sekundaren Dichenwachstums der Baume. Ber. Deutsch. Bot. Gesells. 10: 587-605. 1892. 240 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. . ScHwarz, F., Dickenwachstum und Holzqualitét von Pinus silvestris. 32. 33: 34. 35- BOTANICAL GAZETTE [MARCH Jost, L., Uber Beziehungen zwischen der Blattentwickelung und der Gefassbildung in der Pflanzen. Bot. Zeit. 51:89-138. 1893. , Plant physiology. 1907. p. 294. Kwnupson, L.,. Observations on the inception, season, and duration of cambium development in the American larch. Bull. Torr. Bot. Club 40: 271-293. 1913. Krasse, G. Uber die Beziehungen der Rinderspannung zur Bildung der Jahresringe und zur Ablenkung der Markstrahlen. Sitzb. Akad. Berlin. 1882. , Uber das Wachstum des Verdickungsringes an den jungen Holz- zellen in seiner Abhingigheit von Druckwirkungen. Kraus, E., Die Gewebespannung des Stammes und ihre Folgan. Bot. Zeit. 25:105, 106, 129-137. pl. 2. 1867. Kwy, L., Uber das Dickenwachstum des Holzkorper der Wurzeln in seiner Beziehung zur Lotlinie. Ber. Deutsch. Bot. Gesells. 26:19-50. 1907. MEtssner, R., Studien iiber das mehr jahrige Wachsen der Kiefernadeln. Bot. Zeit. 52:55-82. 1894. , Uber das Verhaltniss von Stamm- und Nadellange bei einigen Coniferen. Bot. Zeit. 59:25-60. 1901. Mer, E., Sur les causes de variation de la densité des bois. Bull. Soc. Bot. France 39: 1892. MiscukE, K., Beobachtungen iiber das Dickenwachstum der Coniferen. Bot. Centralbl. 44:309-43, 65-71. 1890. Von Mont, H., Uber die Abhangigkeit des Wachstums der dicotylen Baume in die Dicke von der physiologischen Thatigkeit der Blatter. Bot. Zeit. 2:89-94, 113-116. 1844. Peterson, O. G., Einige Untersuchungen tiber das Wurzelleben der Baume. Just’s Jahrb. 26:609. 1896. Res, Inaugural Diss. Bonn. 1877. RusBNER, V., Das Hungern des Cambiums und das Aussetzen der Jahr- tinge. Naturw. Zeitsch. Férst. und Landwirtsch. 8:212-262. 19r0. Russow, E., Uber d. Entw. des Hoftiipfels der Membran der Holzzellen und des Jahrringes bei den Abietineen. Sitzb. Dorpat. Natur. Gesells. 1881. Sacus, J., Lehrbuch der Botanik. 1868. Berlin. 1899. STRASBURGER, E., Uber den Bau und die Verrichtung der Leitungsbahnen in d. Pflanzen. 1891. , A text-book of botany. 1912. p. 142. Van TiecHEM, P., Recherches sur la symmetre de structure dans les plantes vasculaires, I, Laracine. Ann. Sci. Nat. Bot. V. 13:5-314. 1870. Ursprunc, A., Uber die Dauer des primaren Dickenwachstums. Ber. Deutsch. Bot. Gesells. 24: 489-497. 1906. NUL PLATE Ha. BOTANICAL GAZETTE, v4 Ce a x re ae ; Liha 2, eet ate ph eae) gigisenue: (iter BROWN on PINUS STROBUS BOTANICAL GAZETTE, LIX PLATE NI¥ ~! BROWN on PINUS STROBUS tors] BROWN—PINUS STROBUS 241 36. DeVries, H. Uber den Einfluss des Drucks auf die Ausbildung des Herbstholz. Flora §5:241-246. 1872; 58:97—-102. 1875. 37. WiEtER, A., Beitr. zur Kenntnis der Jahrringbildung und des Dicken- wachstums. Pringsh. Jahrbiich. 18:70-132. 1887. , Uber die Periodicitat in der Wurzelbildung der Pflanzen. Forstw. Centralbl. 16:333. 1894. , Uber die jihrliche Periodicitat im des Holzkérpers der Baume. Thar. Forstl. Jahrb. 48:39-139. 1808. 38. 39- EXPLANATION OF PLATES XIII AND XIV Fic. 1.—Cutting III taken from tree I, December 22, 1912; cambium and phloem in the resting condition; 75. Fic. 2.—Cutting I taken from tree I, February 20, 1913; phloem (A-B) in winter condition; 160. Fic. 3.—Cutting IV, same; contraction from low temperature more ‘restricted; 160. Fic. 4.—Cutting I taken from tree I, April 26, 1913; growth taking place very rapidly (c, approximate position of the cambium); 100. Fic. 5.—Cutting IT taken from tree I, May 12, 1913; rapid xylem forma- tion has occurred (c, approximate position of the cambium); X so. Fic. 6.—Cutting IV taken from tree I, September 19, 1913; transitional forms of tracheids, slow growth; Xr11o. Fic. 7.—Cutting III taken from tree I, September 26, 1912; autumnal condition of the phloem; X 200. Fic. 8.—Diarch white pine root before secondary thickening; two exarch bundles in process of formation; go. Fic. 9.—Tetrarch white pine root after secondary thickening; X 25. Fic. 10.—Same enlarged, showing 4 original xylem rays; X35. Fic. 11.—Long roots and short roots of white pine, May to, 1913. Fic. 12.—New growth of long roots, May 14, 1913.