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Les diagrammes suivants iilustrent la mdthode. 1 2 3 1 2 3 4 5 6 MlCtOCOPV RESOIUTION TIST CHABT (ANSI and ISO TEST CHART No 21 APPLIED IIVHGE I 1653 Eost Main Street Rochester, Ne* York 14609 uSA (7J6) 482 - OJOO - Phone (716) 288 - 5989 - Fa« .\ 0/ Wew ^.^:^'" ^/ ^I'V OP ««« •S^^ .cy An Undescribed Thermometric Movement of the Branches in Shrubs and Trees '. BY f VV. F. G/.NONG, Ph.D. Profator of Botany ir Smith Colltge. With six Figures in the Text. O OME years ago I noticed an apparent radial movement of the ascendincr ^J branches in certain shrubs and small trees, whereby the branches were brought closer to the main stem in the winter, quite independently of the leat-frll, and were separated from It on the approach of spring. After trying in vain to find some account of this movement, and its causes, in the literature accessible to me^ and from various persons informed on such matters, I undertook a study of it, with results which follow. In the autumn of .898 I chose six shrubs and small trees, in the Botanic Uarden of Smith College, which showed the movement and which were isolated from other woody plants. Selecting long slender branches on the north, south, east, and west sides of -ach plant, I made near the top of each, and on the side radial to the plant, small dots with water-proof India ink, the approximate positions of which were marked for convenience by coloured threads. It was then possible, with the aid of an assistant, to Dec.',^790^^°""" '^°*'yf°'P''"" Morphology and Physiology, at its PhiladclphU Meeting. have'escaLl IT' "'' '';''=' /^'■««"'=«'° '^s movement, although it seems unlikely that it coul.l have escaped not.ce and description ; and the cnly other mention of it that I have been able to securc branches of the Cnkgo The inward movement of the branches after removal of the weight of the ^Z'a' pT" " "" '° ^ "T""" 1° nurserymen; and some measurements of this movement in a shrub arc given m a note by Agnes Krye in Nature, vol. Iv, 1S96, p. lyS and in a bran,.h „f h«, . chestnn. by Miller Christy in Journal of the Linnean sJ^uty, LL'\7, ". .oT-l tZ works of Wieaier, Baranetsky, and others on the determinant, of branch position aonearnorto Jul .hi. subject. Recently Mr. E. F. Bigelow, of Stamford. Conn., has writCrthTtl cordon- dent, of his have asked him the causes of branch movements noticed by them ;.„ one caLitTr* pruce whose branche. rise in wet weather and fall in diy. and in the oth'er it w s a pine wll d" d lAnnal. of Botany, Vol. XVm. No. LXXn. October. 1904.J 6^2 Gattoun^. — Ah Undescribed Thertnometric Movement of measure with a tape the distance between the diametrically opposite marks (i. e. from the north to the south branch, and from the east to the west), and thus to determine any movement the branches might make. The method is illustrated by the accompanying diagram (Fig. 53), The resultant measurements for the four shrubs which showed the most marked move- FiG. 5a. Fig. 53. ment are plotted upon Fig. 54, and the more important figures are contained in the following table: — The riant. Salix laurifolia (about 3 meters high) CtrcidifhyUum jafonicum ^abuut 2 metets bigii) Comus florida (onder a meters high) Brcussonetia paf^tifeia (about 1.5 niclti !iigh) Dale. Condition of Plant. Oct. 10 Nov. I a Jan. ao Apr. a a May a5 June a4 Oct. ic Oct. a8 Jan. ao Apr. aa May a5 June a4 Oct. 10 Nov. I a Jan. ao Apr. 6 May 35 June ; 4 Oct. 10 Nov. la Jan. ao Apr. a a May aj Leaves all on Leaves all gone In full winter condition Buds beginning to swell Leaves all out In full summer condition Leaves all on (nearly) Leaves all gone In full winter condition Buds beginning to >well Leaves nearly all out In full summer condition Leaves all on Leaves all gone III full winter condition Buda swelling Leaves well out In full summer condit-on Leaves all on Leaves all gone In full winter condition No trace of leaves The plant evidently win- ter-killed N.andS. a6i.acm, 257 348.5 245 ayo.5 a93 >'4-.'> 110.5 to6 107 lla 118 '33-3 114.7 >09-5 J'3 lai ■36 1 68. a »5a-4 '4»S «36.5 lag E. and W. 347 cm. 341.7 234 »3» 367 274 ia8 "5-3 1315 laa 138 130 3367 307.3 304 304 317 nh 306.8 187.8 "74-5 'h 150 the Branch'", in Shrubs and Trees. 633 J These measurements showod :— T. A large inward movement accompanyinfj the fall of the leaves, and an outward movement accompanyinfi the formation of new leaves. a. A real seasonal movement independent of leaf-fall and Icaf-fnrma- tion. consisting in an inward movenent during the advancing winter, and an outward movement on the approach of spring. 3. Certain fluctuations in the movements, the reasons for which were n^i: evident. The causes of the movement accompanying leaf-fall and leaf-formation arc so evident as hardly to call for comment ; the movement is simply due to the removal of the weight of the leaves and the!, contained water from the elastic, obliquely-ascending branches in the one case, and the addition of weight in the other. But tlu cause of the further seasonal move- ment of the leafless branches is not at once evident. The measurements showed not only that there is a real movement of the leafless branches, but that it is of considerable amount, rcachin- between leaf-fall and leaf-formation— '^ I a cm., or 5 % of the total diameter of the plant in Salix lauri folia ; 3"-5 cm., or over 3% of the diameter of the plant in Cercidiphyilum jafonicum ; 5^i cm., or over 5 y, of the diameter of the plant in Cvrnus Jlon,fa ; And a larger though uncertain amount in Broussonetia papyrifcra The results were of such interest that a more careful study of the subject was undertaken the following winter (i 899-1900). An improve- ment was made in the method in two respects. First, the movement of each branch was measured separately in order to determine whether there was any difleiencc in the movement of the different branches. This was effected by placing, in all measurements, the loop of the tape l^.^u*^*'''''"^" ^*^^^ **P* ** ""^^ ^^"^ preceding year) over a brass screw held by a cork set in the top of a piece of stout gas-pipe, which was driven firmly mto the ground as nearly as possible in the centre of the shrub (as represented by Fig. sz). It is important to note that this, like any other method of measuring such movements from a fixed point, does not give strictly accurate results, because the marks on the branches do not move in and out along the same radial line, but in different lines. In general however, the errors from this source are very slight, they tend to neutralize one another, and as ? .^hole they affect the results in the direction of „ lesser rather than a greater amount. Secondly, some suggestion having arisen that temperature might have an effect upon the process, the air temperature was recorded at each measurement. The measurements were made by one of my senior students, Miss Phoebe Persons, as often as the weather would permit, throughout the autumn, winter, and spring. One of the greatest difl^culties in this study consists in the fact that the measure- 634 GaitoHs^. — An UndcHribtd Tlurmomdrk Atovimcnt of Fig. m- Abscissa spaces, each two days. Ordinate spaixs, each a-5 mm. of movement. Downward direction me.ins inward of the shrub, and upward means outward. Showing the seasonal movement of four shrubs : — The upper is Salix laurifolia, the second is CerciJif'hyllum japonUum, tlie third is Contus JJorida, the lower is Droussonctia papyrifera. The entire lines arc the north and south measuremcnti the dotted lines are the east and west measurement, the vertical lines across the polygons represent the tin- first .nppearance o.''the leaves from the !ind (the lat The disagreement of Broiasonetia was connected with the death (.w.ntcr-ktlling) of the plunt. complete leaf-fall and of the r Comus was not recorded^. the Jiraiu/ics in S/inibx and Tnrs. 635 ^WP!t}'!litHH|J4i .'!Ti^ , I 1 u. I . . r f / / ' ' . N r K. • / \ 1 N-f't ' ('»t ' ' . t . u ■f i r 1 tt;j+t ^t' - j.;r^iiiteni»!.teJ.fl uflw- i: : .;^... Fig. 55. Aliscissn siiaces, each two days. Ordinate spaces, each i-i, ram. of movement, and I degree of lemperatnre. Downward direction means inward of the shrub, and upward means outward. The plate shows the move.nent of the brunches in two shrubs : The upper is LinJera Htnzoin, the north, south, east, and west branches bete sci ted by the initials N. S. E. \V. The lower is Salix laurifolia, the respective branches being indicated M f< r the *fro. The double line between the two shrubs represents tcmpc-atuic Tie records begin alter the leaves were mostly fallen, and continue until the new le largely formed. X X 636 CiOHjr.^^n Undmribed 7ku..omiinc Afovenunt of ment. can be made, specially when any of the leave, are on onlv In perfectly .t, I weather ; and hence a continuou. .tudy oJ the n.ovement n and It was not attempted by us. ^' ♦,Ki T''? '''"'il '*"'''"*' •^"'''■"»-' ^'"^ ^'"'" ^«™ the seven IJ.ted fn the table bc-Iow. The results of the measurement, of all .even were exceut for mmor differences, very similar, and they are fully illusL^rbv »S / 17Z7ZT''" 7;"?"'^^"'^ °' ''"' •--■-• -^ '^"^^ '--'>/-. wh h to «!-.„, -^ r ""u ''* "''"^'^ '^^ ^"'''''' movement of them a! The to a amphtude of the movement between leaf-fall and Icaf-formubn for all he branches, and the percentage which this movement is ot 1 shrub radius, arc shown by the following table — "^ J'kHt. iyrus americana Sa/ij laiirij'tlia , , i irnits si'riiea .... 6 trcidifhyllum japoniium CornusJIoriJa I.intlera Henzoin Ciiifinus eare/iuianus I Siu in melrtj, ht. diam, I-90X 1-10 ' 4-JOX3.IO iio x 1.90 a-Sox 1-40 »'.10x 1.90 i'6o x 1.30 a-3ox a-oo i AUvtmtnt in ctHlimttrts. Pirttnla^t movimtnl. N. S, E. W. A». N. s. E. W. Av. — »-3 il-a ••4 6.0 .V7 9-4 '.X a-ao M.65 03 ■ a Oi 09 07 10 09 3-J 10 .va a 8 3.9 47 .V05 37J 07 '3 05 oa 04 07 05 oa ?.:^ 5-4 3 ' 8.4 '5 ,07 .13-a 466 371 60 34 .M 34 «-8 4.7 6.6 j 5-3 H 4.8 7-7 4.8 through ^, \ r ."'""""" '^" "^^*=* °f fluctuations of temperaMre through a single day. and the eflfect of the fall of temperature at niX Miss Persons made, after several unsuccessful attempts. 7serLs of measure ments through one still day and part of the next, and f^und hat wZ he" mjts of a single day and night the movement was considerable and tha! rdT ttt^' A^'l'^'-P^^^^-^, ^^-^"- ^^-S'^ lagginglmewt: dir^rt^^V J • ^^ '"'^' "'^ measurements made by her was directed to determine whether the movement was most pronounced L Z ment with any peculiarities of anatomical structure. Iht nranches in Slirubt and Tras. In summ.ir>- the results itiowcci — March, when an outwarcl rovcnlni C '""""^ ^'""^ "^*^-^«" ""'" typical ex , pes on , " l"^. "'T"t"' "^'" »^"'l.cra.ur<. (as shown by the Z a lower „ an .1 V i;i ; ' '■■ *^'"r' ''"" '''^''^ '" «" -"--'•. Within a. single d^yan^'^Kht ""'"'"■'"' "" ""^^^"'^"^ -l.prcciabij agrcLl'rvcrenTi':' '"''";;";-'-,'" ^'- -ovemon., and apparently ThccirTorrcir ',,' ^"^ "■^' "'•»""'-"»•» an.! .est branches. of ten,p:r:;::: tZ' . „; rrii'i^rr^'^^ t^^-^^" ^'-^ ^"-•^- close enough to wirnnt the a. l\ T •""' ""i'^rtant, an.i it i, ««r«. oincc me njiiior m(»venicnt s of tins chAnr ,.r .1,- c.sp„.-.lly a, no precaution, wcc t'to to ,1" K . '"'"Z "■" "'°"-' Icng. nd di«ancc from ,|,e «nl il 00^ F .t . "" "' ""^ -'""•■ did move the mo.t and l,.„™ 1 ?n '"' ""'' ""■" '"•iKhos observed, it seemed o Jn ThTt .1 , ^ 'r ^*=^'^^''"S: the facts so far cither one of he!e £ L 5e I "'^'^ ^"° "'"^'^'"^"^^ -^^^ ^^ .econdary i-war^an^: -2;r.^,::Ls\ l^ Tbe^Xo^^ ^'^^ intensifications and weakenings nf th,. r . / ' ^^^^^porary producing the seasonal ZLentor(7MhtT'1 'T '^""^'^"^^"^^^ causes (or at least to a difference in thlmH'^ T^ " '^"^ '" ^'^^'^^""' causes), the secondary flurtnT V "^^ °^ operation of the same special causes eXro^tfrol"%^"^u''"P°'''^>' movements due to rhe facts at our command see„,ed at first to puint to the la, !r X X 2 638 Ganong. — An Undescribed Tltermotnetric Movement of probability, and in order to obtain a definite basis for experiment we assumed that the secondary fluctuations were simply outward movements from the seasonal position. As a physical (or mechanical) cause of this outward movement under higher temperature, it seemed to us likely that the warming up, "w-i consequent swelling, of the inner faces of the long slender branches under the influence of the sunlight on the warmer days was sufficient. Evidently this hypothesis could be submitted to experi- ment, for not only ought the outward movement to be greater on a sunny than upon a cloudy day of approximately the same temperature, but the movement in branches illuminated at the time of measurement on their inner faces should show more movement than those at that time shaded, or, still better, than those illuminated upon their outer faces. Simple as such a test appears the weather never allowed us to put it to satisfactory use, and the season closed without its accomplishment. The following winter, 1900-1, I was occupied with other matters and did nothing with this subject; but the next year, 1901-2, 1 resumed the study. Influenced by the theory above mentioned, I prepared to make more exact measurements than before of the respective movements of the four branches, for it was evident the theory could be tested by observing whether, as it requires, the greatest amplitude of movement occurs in the north branches, the next greatest in that east or west branch which happened to be illuminated on its inner face, and the least in the south branches. I made an improvement in Miss Persons's method by re- placing the single gas pipe, which would yield a little under tension when the tape was drawn tight, by a perfectly firm tripod, formed of three gas pipes driven deeply into the ground, and bound immovably at their tops by twisted copper wire into which the brass screw was set, an arrangement illustrated diagrammatically in Fig. 56. Throughout the winter very careful measurements were made of six shrubs, including the Lindera and Cercidiphyllum used the previous winter, together with two species of Salix and two species of Populus (young trees). The results need not here be given in detail, since in general they are simply confirmatory of those earlier obtained. As to the two main points at issue they were as follows : — I . There was no such regularity or order in the amplitudes of move- ment of the respective branches as the theory required. a. There was no regular influence produced upon the movements by the presence or absence of direct sunlight upon the faces of the branches, Fig. 56. the Branches in Shrubs and Trees. 639 /\ though in some individual cases this did appear to have some slight effect. It occurred to me during the winter, especially when it became plain that the direct sunlight played little part, that perhaps the movement might be due to a warming, and hence swelling, of the inner faces of all the branches through a general warming up of the air among the branches of the shrub due to the reflection of the sun's heat from one branch to another. To test this I placed very accurate thermometers, reading precisely alike and graduated to tenths of a degree, both near the centre of the shrub (but in the sun), and outside the shrub a few feet away. They showed that the temperature among the branches and that outside the shrub were not appreciably different, thus eliminating another possible cause of the movement. The idea that a direct action of the sun upon the plant produced the movement had therefore to be abandoned. The following winter, 1902-3, I continued the study, concentrating attention upon two plants, Lindera Benzoin and a species of Salix, which had shown themselves particularly sensitive to temperature changes. In- cidentally I re-measured these two shrubs very carefully through the winter, and the results for Lindera are given on Fig. 57, not because they bring out anything new, but because they show with particular clearness the correlation of movement with temperature. But the principal work during the winter was experimental, and directed to discover the precise physical basis of the movement. Its results were as follows. Certain observations made while measuring the shrubs seemed to render it probable that the outward movement was caused by the straightening of the curved branches due to the swelling of the air, and perhaps also the water, in the stems under the influence of the higher temperature. A marked swelling of this kind should produce a straightening of the branch upon precisely the same principle as it straightens the bulb of a Richard thermograph. This could be tested by bringing typical curved branches from the shrubs on very cold days directly into a warm greenhouse, and comparing the distance between the base and tip before and after the branch had time to warm up. I tried this in a variety of ways, even bringing them abruptly from a temperature much below 0° (C.) directly into a large case kept at a temperature above 30°. To make the conditions as to water supply as uniform as possible, I plunged the branches at once into water in some cfises (cutting them under water higher up the stem in some instances), and immediately sealed the cut ends with shellac in others. The results in all cases were the same. A slight straightening could often be observed within a few minutes under the higher temperature, but this was always lost within an hour or there- abouts, and was then replaced by a gradually increasing curvature. It became plain, therefore, that while a rise in temperature might cause 640 Ganong.—An Undescribed Thermometric Movement of Fig. 57. Abscissa sjMces of upper five polygoni, each two days; of lower six polygons, one half-day Ordinate spaces, each 2 mm of movement (thus differing slightly from two preceding plates) and 1 degree of temperature, and 1% of water (for lower polygon). Downward direction means inward of the shrub, and upward means outward. The plate shows the movement of the branches of LincUra Benxoin, the north, south eait and west branches being indicated by the initials N. S. E. W. The upper four polygons show the movement through the season, and the four below them show it upon a larger lateral scale through the period of greatest secondary movement. The double line represents temperature. The lowermost line represents the percentage of water contained in Saiix. (On irregularities in this plate see note on page 644.) the Branches in Shrubs and Trees. 641 a slight straightening and hence outward movement, which might in the uninjured plant remain constant, such a cause was wholly insufficient to account for the entire amount of movement. That the swelling of air in the stem did not produce the result was proven by forcing air powerfully into the stem with a foot pump, a process always without appreciable result. Having thus to abandon this hypothesis I turned to another, more than once taken up and dropped in the earlier part of the study, that the movement was in some way connected with the quantity of water present in the stem. This was, indeed, very strongly indicated by two facts: (a) the Bt oussonetia earlier referred to (p. 634) showed a continuous in- curving of its branches after the plant was dead, which incur\'ing was apparently correlated with the drying out of the branches ; and {b) invariably during the experiments a drying out of any branch was accompanied by an incurving, that is, by an inward movement. The incurved, or extreme inward position, is evidently the natural position of the dry tissues, and it seemed probable, therefore, that the outward movement might be corre- lated with, and proportional to, the amount of water in the stem. This supposition could evidently be readily submitted to experiment. Accord- ingly on certain days showing extreme outward and inward movement, and therefore of extreme high and low temperature, during the winter, I cut from each of these shrubs ten healthy branches each 10 cm. long, tied them in bunches, and immediately weighed the latter. They were then dried for several months in a dry room, and subsequently for some days in a water bath. They were then again weighed, and the percentage of water in the original branches was thus readily determined. The results were as follows : — Dale. Jan. 19 Jan. 32 Feb. ao Feb. 31 Feb. 34 Mar. 13 Temp. -18 8 -II -»5 5 J5 Plant. Lindera Salix ILindtra Salix ! Lindera Salix Lindera ! Lindera Salix i Lindera Salix Original Weight. 3-99« 2-960 3<5i8 2613 4.027 4-03» 357* 3-8S4 3-830 2870 Dry Amount Percentage Weight. of Water. of Water. J-S." '•4.^9 36-0 I-i«72 1-388 46.8 3-281 '•347 37-1 «-.l7« 1.343 47-5 a-4<>5 i.,s6a 38-7 1.490 1195 46.4 2-494 1538 381 3-220 J-35» S.vo '•533 1.361 47-1 2.073 1.748 45-7 '•483 1-387 48-3 Comparison oi these figures with the amount of movement at the corresponding dates (as shown on Fig. 57) will show at once that in Salix the agreement between amount of water and amplitude of movement is very close, a fact graphically illustrated by the polygon at the foot of 642 Ganong, — An Undescribed Thermometric Movement of Fig. 57. In Under a, however, while there is agreement in some places, there is a wide deviation in others, so it becomes plain that either my figures are in error or else this method is worthless. There is, however, this difference between the two plants, that as the Under a dries it loses some of its buds and bud-scales, while the Salix does not, and my method of drying the stems did not originally allow for this possible source of error. Despite the lack of agreement in the Lindera, however, I believe that the testimony of the Salix, and also that afforded by the gradually increasing curvature of all branches as they lose water, indicates a fundamental fact, namely, that the movement is connected with the amount of water in the stem, and that this amount of water is dependent upon temperature. This conclusion involves two further questions ; (i) by what mechanical method does the increased amount of water produce the movement ; and (3) by what method does the variation in temperature produce a variation in the amount of water ? We consider first the former, for whicli there are two possible explanations: (a) the weight of an added quantity of the water will tend to depress the obliquely-ascending branches and may thus produce the outward movement ; {b) the added water may permit of the larger absorption by the various cells of the younger branches and their consequent swelling, whereby the straightening of the stem must result, precisely as any flaccid tissue straightens with more abundant water- content. I have carefully tested both of these possibilities. As to the first I have repeatedly placed branches horizontal, and forced water into them both under an atmosphere of mercury, and also under the greater pressure of the water directly from a water tap. In such cases the water would be forced out in a few minutes from any injury incidentally or purposely made near the tip of the stem, showing that the water penetrated to the end. In such a case a distinct depression of the branch can usually be measured, but it is never of an amount as great as the natural amplitude of the movement in the branch attached to the plant. Furthermore, this small amount of movement occurs in the most favourable possible position (horizontal) of the branch, and would be much less when the branch is partially upright upon the tree. When the branches are placed upright, and the water is then forced into them, there is very little, if any, measurable movement. There is yet another consideration which shows that it cannot be the weight of the water which causes the outward movement, namely, that in many of the shrubs which showed marked movement of the branches the latter are nearly vertical as a whole, and hence the weight of the water cannot act to move them outward. The weight of the water, therefore, may aid the movement somewhat, but it cannot be the principal factor in causing it. We turn now to the other explanation, that an added supply of water the Branches in Shrubs and Trees. 643 permits a more active absorption by the cells (osmotic absorption bv the hving, and imbibition by the walls of the dead, cells) and their consequent svvellmg, thus producing a straightening and therefore an outward movement of the branch. The inward movement would be caused by a lesser absorp- tion which would permit the loss by transpiration to exceed absorption and hence render the cells flaccid, permitting the branch to assume its natural curve. That there is a steady loss of water from the twigs during the winter, including even the coldest weather is, I believe, well known. I have myself noted that, on the coldest days in the winter on which measurements were made, little ice crystals stood upon the lenticels of both Lindera and Salix. Now this steady loss of water implies a steady, even though small, absorption through the winter. It is well known, however that with decreasing temperature the power of osmotic absorption falls much more rapidly than the rate of transpiration ; hence with a falling temperature the loss of water from the parenchyma cells becomes in- creasingly great as compared with the possibility of renewing the supply osmotically; the turgidity of the cells must then decrease, and the same effect will follow as if the stem is dried out by any other method, namely. Its curvature is increased and hence an inward movement results. The lagging of the movement behind the temperature-changes, earlier men- tioned, is strongly in confirmation of this view. Unfortunately, my attempts to test this hypothesis experimentally have given very unsatisfactory results, so that I am unable to either confirm or disprove it, and as further experiment is not now possible until another winter, I must leave its com- pletion to a future time or to others. But I regard this as by far the most probable explanation of the movement. Turning to the question as to how a higher temperature increases the water-content of the stem, it is obvious that this is bound up with the still unsolved problem of the physics of sap-ascent. The roots of these shrubs extend down below the frost line in the soil, so there is no difficulty as to the root supply. The explanation here attributed to the movement obviously applies to both seasonal and secondary uations, and would make them the result of the same causes. As to the significance of the movement to the plant, I think the probabilities are that the movement is a purely physical phenomenon, merely an incidental result of the operation of a physical agency upon the mechanism the plant happens to present, and that it has no ecological advantage. It must be noted, however, that it still remains a possibility that the movement may be due to a differential absorption of water, this occurring more actively in the cells on the inner than on the outer faces of the branches, in which case it might not belong under incidental or physical, but under irritable movements, when it would be removed from the ther- 644 GanoKs.—Undeseribed Thermometric Movement of Brancfies. momctric toward, the thermotropfc category. If this should prove lo be true ,t W.11 render it probable that the movement has some ecological value The inward movement of the branches might be supposed to be protective, decreasing slightly the leverage of winter winds upon thern. and as well the X\ *u . "^^ '°" °^ ****'' ^"* ^ ''•B''t « the amount of movement that the advantage can hardly be appreciable. Since it is not the application of heat directly which determines the movement, but an indirect action through water absorption, it might be more exact to speak of the movement as an indirect thermometric movement. In summary: — {a) Some shrubs and small trees, and probably very many, exhibit a marked mward and outward movement of their naked winter branches. Kb) Two forms of the movement occur, a primary or seasonal move- ment, inward during the early part of the winter and outward in spring, and a secondary movement which is inward with a fall and outward with a rise of temperature. Probably these two are due to the same causes, the seasonal being simply a secondary movement of laige a.nplitude. {c) The movement is correlated with changes of temperature, though It is not caused by temperature directly, but by the larger or smaller quan .ties of water which the temperature determines in the plant. A smaller quantity of water, due to transpiration exceeding absorption, decre ;e. turgidity and permits the natural inward spring of the branches to manifest Itself, while a larger quantity, due to absorption exceeding transpiration, permits an increase of turgidity and consequent swelling, straightening, and outward movement of the stem. & & s. " (