Project Gutenberg's Life Movements in Plants, by Sir Jagadis Chunder Bose This eBook is for the use of anyone anywhere at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this eBook or online at www.gutenberg.org/license Title: Life Movements in Plants Author: Sir Jagadis Chunder Bose Release Date: February 16, 2015 [EBook #48280] Language: English Character set encoding: UTF-8 *** START OF THIS PROJECT GUTENBERG EBOOK LIFE MOVEMENTS IN PLANTS *** Produced by Bryan Ness, Thiers Halliwell and the Online Distributed Proofreading Team at http://www.pgdp.net Transcriber’s notes: In this transcription a black dotted underline indicates a hyperlink to a page, illustration or footnote; hyperlinks are also marked by aqua highlighting when the mouse pointer hovers over them. A red dashed underline indicates the presence of a concealed comment which, in the html version, can be revealed by hovering the mouse pointer over the underlined text. Page numbers are shown in the right margin. Footnotes are located at the end of the book. The text contains typographic characters that will not necessarily display correctly with all viewing devices. If some of the characters look abnormal, first ensure that the device’s character encoding is set to Unicode (UTF- 8). The default font might also need to be changed to a Unicode font such as Arial Unicode MS, DejaVu, Segoe UI Symbol or FreeSerif. Many of the illustrations in the book were of poor quality and a few had no visible useful information. Where possible, they have been enhanced to clarify the details. Alphabetic labels in the illustrations occasionally differ from those stated in the accompanying captions. Some illustrations have been relocated closer to the relevant text and the list of illustrations has been amended as necessary. Discrepancies between the Table of Contents and headings in the body of the text are as in the original. Inconsistencies in the use of single and double quotation marks are as in the original; other punctuation anomalies have been corrected silently. Missing degree (°) symbols have been inserted where necessary. Minor spelling inconsistencies are as in the original, e.g. tetanising/tetanizing, Das/Dass, but the following overt spelling errors have been corrected silently: his —> this despressing —> depressing presistent —> persistent actic —> lactic excitabilitty —> excitability Zephyanthes —> Zephyranthes fal —> fall tranmission —> transmission substracting —> subtracting issue —> tissue conducing —> conducting ummasking —> unmasking be —> been end —> and flexture —> flexure tentanising —> tetanising anisotrophy —> anisotropy The cover image of the book was created by the transcriber and is placed in the public domain. Book cover LIFE MOVEMENTS IN PLANTS BY SIR JAGADIS CHUNDER BOSE, Kt., M.A., D.Sc., C.S.I., C.I.E., PROFESSOR EMERITUS, PRESIDENCY COLLEGE, DIRECTOR, BOSE RESEARCH INSTITUTE. WITH 92 ILLUSTRATIONS B.R. Publishing Corp. Delhi Cataloging in Publication Data-DK Bose, Jagadish Chandra, 1858–1937. Life movements in plants. Reprint. 1. Plants—Irritability and movements. 2. Growth (Plants). 3. Plants—​Develop​ment. 4. Botany. I. Title. First Published 1918 Reprinted 1985 Published in India by B.R. PUBLISHING CORPORATION 461, VIVEKANAND NAGAR, DELHI-110052 (INDIA) Distributed by D.K. PUBLISHERS’ DISTRIBUTORS 1, ANSARI ROAD, DARYA GANJ, NEW DELHI-110002 (INDIA) PHONE: 27-8368 Printed at: BRITE PRINTERS NEW DELHI-110005 (INDIA) CONTENTS PART I. RESPONSE OF PLANT ORGANS. I.—THE PROBLEM OF MOVEMENT IN PLANTS. PAGE Complexity of the problem—Effects of different forms of stimuli—Diverse responses under identical stimulus—Modification of response determined by intensity and point of application of stimulus, and tonic condition of organ—Response of pulvinated and growing organs—Necessity for shortening the period of experiment 1 II.—THE “PRAYING” PALM TREE. Description of phenomenon—The Recording apparatus—Record of diurnal movement of the tree— Universality of tree movement—Cause of periodic movement—Periodic movement of trees, and diurnal variation of moto-excitability in Mimosa pudica—Relative effects of light and temperature— Physiological character of the movement—Transpiration and diurnal movement—Diurnal movement in inverted position—Effect of variation of temperature on geotropic curvature—Reversal of natural rhythm by artificial variation of temperature 5 III.—ACTION OF STIMULUS ON VEGETABLE TISSUES. Different types of Response Recorders—Response of a radial organ—Response of an anisotropic organ—Response of pulvinus of Mimosa pudica—Tabular statement of apex time and period of recovery in different plants—Response of pulvinus of Mimosa to variation of turgor—Different modes of stimulation 31 ii IV.—THE DIURNAL VARIATION OF EXCITABILITY IN MIMOSA. Apparatus for study of variation of excitability—Uniform periodic stimulation—The Response Recorder —Effects of external condition on excitability—Effects of light and darkness—Effect of excessive turgor—​Influence of temperature—​Diurnal variation of ex​cit​abil​ity—​Effect of physio​logic​al inertia 43 V.—RESPONSE OF PETIOLE-PULVINUS PREPARATION OF MIMOSA. Effect of wound or section in modification of normal excitability—The change of excitability after immersion in water—Quantitative determination of the rate of decay of excitability in an isolated preparation—Effect of amputation of upper half of the pulvinus—Effect of removal of the lower half —Influence of weight of leaf on rapidity of responsive fall—The action of chemical agents—Effect of “fatigue” on response—The action of light and darkness on ex​cit​abil​ity 73 VI.—CONDUCTION OF EXCITATION IN PLANTS. Hydro-dynamic versus physiological theory of conduction of excitation—Arrest of conductivity by physiological blocks—Convection and conduction of excitation—Effect of temperature on velocity— Effect of season—Effect of age—Effect of dessication of conducting tissue—Influence of tonic condition on conduction—​Effect of intensity of stimulus on velocity of trans​mission—​Effect of stimulus on sub-tonic tissues and tissues in optimum condition—Canalisation of conducting path by stimulus— Effect of injury on conductivity 97 VII.—ELECTRIC CONTROL OF EXCITATORY IMPULSE. Method of conductivity-balance—Control of transmitted excitation in Averrhoa bilimbi by electric current—‘Uphill’ transmission—Transmission ‘downhill’—Electric control of nervous impulse in animal—Directive action of current on conduction of excitation—Effects of direction of current on velocity of transmission in Mimosa—Determination of variation of conductivity by method of Minimal Stimulus and Response—Influence of direction of current on conduction of excitation in animal nerve —Variation of velocity of transmission—After-effects on Heterodromous and Homodromous currents—Laws of variation of nervous conduction under electric current 107 VIII.—EFFECT OF INDIRECT STIMULUS ON PULVINATED ORGANS. Conduction of excitation—Dual character of the transmitted impulse—Effect of distance of application of stimulus—Periods of transmission of positive and negative impulses—Effects of Direct and Indirect stimulus 135 IX.—MODIFYING INFLUENCE OF TONIC CONDITION ON RESPONSE. Theory of assimilation and dissimilation—Unmasking of positive effect—Modification of response under artificial depression of tonic condition—Positive response in sub-tonic specimen 141 PART II. GROWTH AND ITS RESPONSIVE VARIATIONS. X.—THE HIGH MAGNIFICATION CRESCOGRAPH FOR RESEARCHES ON GROWTH. Method of high magnification—Automatic record of the rate of growth—Determination of the absolute rate of growth—Stationary method of record—Moving plate method—Precaution against physical disturbance—Determination of latent period and time-relations of response—Advantages of the Crescograph—​Magnetic amplification—​The Demonstration Crescograph 151 XI.—EFFECT OF TEMPERATURE ON GROWTH. Method of discontinuous observation—Method of continuous observation—Determination of the cardinal points of growth—​The Thermocrescent curve—​Relation between temperature and growth 173 XXII.—EFFECT OF CHEMICAL AGENTS ON GROWTH. Effect of stimulants—Effect of anæsthetics—​Action of different gases—​Action of poisons 183 XIII.—EFFECT OF VARIATION OF TURGOR AND OF TENSION ON GROWTH. Response to positive variation of turgor—Method of irrigation—Effect of artificial increase of internal hydrostatic pressure—Response to negative variation of turgor—Method of plasmolysis—Effect of alternative variations of turgor on growth—Response of motile and growing organs to variation of turgor—​Effect of external tension 188 iii iv v XIV.—EFFECT OF ELECTRICAL STIMULUS ON GROWTH. Effect of intensity—Effect of continuous stimulation—Continuity between ‘incipient’ and actual contraction—​Immediate effect and after-effect 195 XV.—EFFECT OF MECHANICAL STIMULUS ON GROWTH. Effect of mechanical irritation—Effect of wound 200 XVI.—ACTION OF LIGHT ON GROWING ORGANS. Method of experiment—Normal effect of light—Determination of the latent period—Effect of intensity of light—​Effect of continuous light—​Effects of different rays of the spectrum 205 XVII.—EFFECT OF INDIRECT STIMULUS ON GROWTH. Mechanical and electrical response to Indirect Stimulus—Variation of growth under Indirect Stimulus— Effects of Direct and Indirect Stimulus 213 XVIII.—RESPONSE OF GROWING ORGANS IN STATE OF SUB-TONICITY. Theory of assimilation and dissimilation—Unmasking of positive effect—Modification of response under artificial depression of tonic condition—Positive response in sub-tonic specimen—Abnormal acceler‐ ation of growth under stimulus—Continuity between abnormal and normal responses—Positive response to sub-minimal stimulus 219 XIX.—RESUMPTION OF AUTONOMOUS PULSATION AND OF GROWTH UNDER STIMULUS. Resumption of pulsatory activity of Desmodium leaflet at standstill—Renewal of growth under stimulus —​General laws of effects of Direct and Indirect Stimulus 227 XX.—ACTION OF LIGHT AND WARMTH ON AUTONOMOUS ACTIVITY. The Oscillating Recorder—Record of pulsation of Desmodium gyrans—Effect of diffuse light in diminution of amplitude and reduction of diastolic limit of pulsation—Antagonistic action of warmth in reduction of systolic limit 233 XXI.—A COMPARISON OF RESPONSES IN GROWING AND NON-GROWING ORGANS. Contractile response of growing and non-growing organs—Time-relations of mechanical response of pulvinated and growing organs—Similar modification of response under condition of sub-tonicity— Opposite effects of Direct and Indirect stimulus—Exhibition of negative electric response under Direct, and positive electric response under Indirect stimulus—Similar modification of autonomous activity in Desmodium gyrans and in growing organs under parallel conditions—Similar excitatory effects of various stimuli on pulvinated and growing organs—Similar discriminative excitatory effects of various rays in excitation of motile and growing organs—Action of white light—Action of red and yellow lights—Action of blue light—Action of ultra-violet rays—Action of infra-red rays—Diverse modes of response to stimulus—Mechanical response—Electromotive response—Response by variation of electric resistance 239 ILLUSTRATIONS. FIGURE. PAGE. 1. Photographs of morning and evening positions of the ‘Praying Palm’ 7 2. The Recording Apparatus 9 3. Record of diurnal movement of the ‘Praying Palm’ 11 4. " " " Sijbaria Palm 12 5. Curve of variation of moto-ex​cit​abil​ity in Mimosa pudica 17 6. Effect of physio​logic​al depression on diurnal movement of Arenga saccharifera 19 7. Record of diurnal movements of young procumbent stem of Mimosa pudica 26 8. Erectile response of Basella to gradual fall of temperature 28 9. Responsive fall of Basella to gradual rise of temperature " 10. Response of a straight tendril of Passiflora 33 11. Response of a hooked tendril of Passiflora 35 vi 12. Response of pulvinus of Mimosa pudica 36 13. " " Mimosa to variations of turgor 40 14. Diagram of complete apparatus for record of diurnal variation 46 15. The Oscillator 50 16. Effect of cloud on ex​cit​abil​ity of Mimosa 52 17. Effect of sudden darkness 53 18. Effect of change from darkness to light 54 19. Effect of enhanced turgor 55 20. Effect of moderate cooling 56 21. Effect of application of intense cold 58 22. Effect of temperature above the optimum 58 23. Twenty-four hours’ record of ex​cit​abil​ity of Mimosa 59 24. Midday record from noon to 3 p.m. 62 25. Evening record from 6 to 10 p.m. 63 26. Morning record from 8 a.m. to 12 noon 64 27. Diurnal variation of ex​cit​abil​ity showing marked nyctitropic movement 65 28. Diurnal curves of temperature and of corresponding variation of ex​cit​abil​ity of Mimosa 68 29. Diurnal variation of ex​cit​abil​ity of a summer specimen 70 30. The Resonant Recorder 76 31. Variation of ex​cit​abil​ity after section 80 32. Effect of amputation of upper half of pulvinus of Mimosa 84 33. Response of Mimosa after amputation of lower half of pulvinus 86 34. Effect of weight on rapidity of fall 87 35. Stimulating action of Hydrogen peroxide 88 36. Incomplete recovery under the action of BaCl and transient restoration under tetanisation 89 37. Antagonistic action of alkali and acid 90 38. Fatigue due to shortening of recovery-period 91 39. Effect of constant current in removal of fatigue 92 40. Stimulating action of light and depressing action of darkness 94 41. Action of glycerine in enhancing speed and intensity of transmitted excitation in Mimosa 102 42. Effect of injury in depressing conductivity in normal specimen 104 43. Effect of injury in enhancing conductivity in a subtonic specimen 105 44. Diagram of experimental arrangement for conductivity control in Averrhoa bilimbi 109 45. Diagram of complete experimental arrangement for conductivity control in Mimosa pudica 116 46. Record showing enhanced velocity in ‘up-hill’ and retarded velocity in ‘down-hill’ trans​mission 121 47. Direct and after-effect of hetero​dromous and homo​dromous currents 124 48. Diagram of experimental arrangement for variation of conductivity of animal nerve 126 49. Effect of hetero​dromous and homo​dromous current in inducing variation of conductivity in nerve 127 50. Record of ineffectively transmitted salt-tetanus becoming effective under hetero​dromous current 129 51. Direct and after-effect of homo​dromous current 131 52. Effect of indirect electric stimulus on the responding leaflet of Averrhoa 136 53. Staircase responses of sub-tonic specimen of Mimosa to electric shock 145 54. Staircase responses of sub-tonic specimen of Mimosa to light 147 55. Positive, diphasic, and negative responses of extremely sub-tonic specimen of Mimosa to successive light stimuli 147 56. The compound Lever 154 57. The crank arrangement for oscillation 156 58. Photograph of the High Magnification Crescograph 157 59. Crescographic record of absolute rate of growth of Kysoor, and of effects of cold and warmth on stationary and moving plates 161 60. Record of physical change 164 61. Records of latent period and time relations of growth response 165 62. Record of a single growth-pulse of Zephyranthes 167 63. Records of growth-rate at different temperatures 175 64. Continuous record of growth, showing temperature minimum 178 65. Continuous record of growth, showing temperature maximum " 66. The Thermo-Crescent Curve 180 67. Curve showing the relation between growth and temperature 181 68. Effects of H O , NH , and ether on growth 184 69. Effect of CO on growth 185 70. Effect of irrigation on growth 189 71. Effect of plasmolysis on growth 191 72. Effect of increasing intensity of electric stimulus on growth 196 73. Effect of continuous electric stimulation on growth 197 74. Immediate and after-effects of friction, and of wound on growth 200 viii 2 ix 2 2 3 2 x 75. Normal retarding effect of light on growth 206 76. Record showing latent period of growth in response to light 207 77. Effect of light of increasing intensities 208 78. Continuous effect of light and of electric stimulus on growth 209 79. Effects of different rays of the spectrum on growth 210 80. Photographic records of positive, diphasic and negative electric responses of petiole of Musa 214 81. Record of growth variation of Crinum under Direct and Indirect stimulus 216 82. Effect of electric stimulus on sub-tonic specimen of wheat seedling 221 83. Acceleration of growth under sub-minimal stimulus of light 224 84. Revival by stimulus of light of autonomous pulsations of Desmodium gyrans at stand still 228 85. Renewal of growth in the mature style of a flower by the action of stimulus 229 86. Effect of light in diminution of amplitude and reduction of diastolic limit of pulsation of Desmodium 236 87. Antagonistic effect of warmth in reduction of systolic limit 237 88. Contractile response of a growing bud of Crinum 241 89. Response of Mimosa pulvinus to white light 245 90. Response of Mimosa pulvinus to blue light 246 91. Response of Mimosa pulvinus to ultra-violet rays 247 92. Response of Mimosa pulvinus to thermal radiation 248 PART I. RESPONSE OF PLANT ORGANS. I.—THE PROBLEM OF MOVEMENT IN PLANTS By Prof. Sir J. C. Bose. The phenomenon of movement in plants under the action of external stimuli presents innumerable difficulties and complications. The responding organs are very different: they may be the pulvini of the ‘sensitive’ or those of the less excitable leguminous plants; the petioles of leaves, which often act as pulvinoids; and organs of plants in a state of active growth. Taking first the case of the pulvinus of Mimosa, we find that it responds to mechanical stimulation, to constant electric current, to induction shock, to the action of chemical agents, to light, and to warmth as differentiated from thermal radiation. The reactions induced by these agents may be similar or dissimilar. An identical agent, again, may give rise to movements which are not merely different, but sometimes even of diametrically opposite characters. Certain organs, for example, direct themselves towards light, others away from it. Some plants close their leaflets on the approach of darkness, in the so-called position of ‘sleep’; apparently similar ‘sleep’ movement is induced in others by the action of the midday sun. In Mimosa, the responsive movement is brought about by a sudden diminution of turgor in the pulvinus. But very little is definitely known about the responsive reaction in growing organs. Thus in a tendril, one-sided contraction causes a shortening of the concave side and a sudden increase of growth on the convex. No explanation of this difference has hitherto been forthcoming. Under the action of light of different intensities a growing organ may approach the source of light, or place itself at right angles or move away from it. Again under the identical stimulus of gravity, the root moves downwards, and the shoot upwards. The sign of response in different organs thus changes, apparently without any reason. It is thus seen, that there is hardly any responsive movement that has been observed of which an example directly to the contrary may not be found. For this reason it has appeared hopeless to unify these very diverse phenomena, and there has been a tendency towards a belief that it was not any definite physiological reaction, but the individuality of the plant that determines the choice of its movement. The complexities which baffle us may, however, arise from the combination of factors whose individual reactions are unknown to us. I shall show, for example, how the movement of a pulvinus under a given stimulus is determined by the point of application, direct stimulus producing one effect, and indirect the diametrically opposite. The normal reaction is again modified by the tonic condition of the plant. There is again the likelihood of the presence of other modifying factors. It is clear how very different the results would become by the permutation and combination of these diverse factors. For a comprehensive study of the phenomenon of plant movement, it is therefore necessary to investigate in detail the effect of a given stimulus under definite changes of the environmental condition. With regard to a given stimulus we have to determine the effects of intensity, of duration, and of the point of application. The investigation has to include the 2 3 effects exhibited not merely by the pulvinated but also by growing organs. As a result of such a comprehensive study, it may perhaps be possible to discover some fundamental reaction operative in bringing about the responsive movement in all plant organs. I shall in the course of the following series of Papers, describe the different apparatus by which the movement of pulvinated organ and its time-relations are automatically recorded. In a growing organ the induced movement under stimulus is brought about by the change in its rate of growth. That the change is solely due to the particular stimulus can only be assured by strict maintenance of constancy of external conditions, during the period of experiment; this constancy can, in practice, be secured only for a short time. The necessity for shortening the period of experiment also arises from a different consideration; for numerous and varied are the stimulating and mechanical interactions between neighbouring organs. These effects, however, come into play after a certain lapse of time. They may be eliminated by reduction of the period of experiment. In order to shorten the period of experiment for the study of growth movements, the rate of growth has to be very highly magnified, so as to determine the absolute rate and its variations in the course of a minute or so. I shall in a subsequent Paper give full account of an apparatus I have been able to devise, by which it is possible to record automatically the rate of growth magnified many thousand times. I stated that anomalies of plant movements would disappear, if we succeeded in carrying out in detail investigations of effects of the different individual factors in operation. In illustration of this I shall, in the first Paper of the series, give an account of the mysterious movement of the ‘Praying’ Palm of Faridpur, and describe the investigations by which the problem found its solution. II.—THE “PRAYING” PALM TREE By Sir J. Bose, Assisted by Narendra Nath Neogi, M.Sc. Perhaps no phenomenon is so remarkable and shrouded with greater mystery as the performances of a particular Date Palm near Faridpur in Bengal. In the evening, while the temple bells ring calling upon people to prayer, this tree bows down as if to prostrate itself. It erects its head again in the morning, and this process is repeated every day of the year. This extraordinary phenomenon has been regarded as miraculous, and pilgrims have been attracted in large numbers. It is alleged that offerings made to the tree have been the means of effecting marvellous cures. It is not necessary to pronounce any opinion on the subject; these cures may be taken as effective as other faith-cures now prevalent in the West. This particular Date Palm, Phœnix dactylifera, is a full-grown rigid tree, its trunk being 5 metres in length and 25 cm. in diameter. It must have been displaced by storm from the vertical and is now at an inclination of about 60° to the vertical. In consequence of the diurnal movement, the trunk throughout its entire length is erected in the morning, and depressed in the afternoon. The highest point of the trunk thus moves up and down through one metre; the ‘neck,’ above the trunk, is concave to the sky in the morning; in the afternoon the curvature disappears, or is even slightly reversed. The large leaves which point high up against the sky in the morning are thus swung round in the afternoon through a vertical distance of about five metres. To the popular imagination the tree appears like a living giant, more than twice the height of a human being, which leans forward in the evening from its towering height and bends its neck till the crown of leaves press against the ground in an apparent attitude of devotion (Fig. 1). Two vertical stakes, each one metre high, give a general idea of the size of the tree and movements of the different parts of the trunk. 4 5 6 7 Fig. 1. The Faridpur ‘Praying’ Palm; the upper photograph shows position in the morning; the lower, position in the afternoon. The two fixed stakes are one metre in height. In front is seen erect trunk of a different Palm. For an in​ves​ti​ga​tion in elucidation of this phenomenon it was necessary:— 1. To obtain an accurate record of the movement of the tree day and night, and determine the time of its maximum erection and fall. 2. To find whether this particular instance of movement was unique, or whether the phenomenon was universal. 3. To discover the cause of the periodic movement of the tree. 4. To find the reason of the remarkable similarity between the diurnal movement of the tree, and the diurnal variation of moto-ex​cit​abil​ity in Mimosa pudica. 5. To determine the relative effects of light and temperature on the movement. 6. To demonstrate the physio​logic​al character of the movement of the tree. 7. To discover the physio​logic​al factor whose variation determines the directive movement. THE RECORDING APPARATUS. I shall now describe the principle and construction of my recording apparatus (Fig. 2) seen attached to a horizontally growing stem of Mimosa pudica. When used to trace the movement of the palm tree, a reducing device is employed to keep the record within the plate. A lever, R′, records the movement of the attached tree or plant on a moving plate of smoked glass. The plate is not in contact with the tip of the recording lever, but separated from it by a distance of about 3 mm. A special oscillating device, actuated by clock-work, C, makes the plate move forwards and backwards. The forward movement brings about a momentary contact of the recording tip with the smoked plate inscribing a dot. These single dots are made at intervals of 15 minutes; at the expiration of the hour, however, contact is made three times in rapid succession, printing a thick dot. It is thus easy to determine the movement of the tree at all times of the day and night. A second lever, R, placed above, gives on the same plate, thermographic record of the diurnal variation of temperature. For this I use a differential thermometer, T, made of a compound strip of brass and steel. Curvature is induced by the differential expansion of the two pieces of metal. The up or down movement of the free end of the 8 9 compound strip is further magnified by the recording lever. This arrangement was extremely sensitive and gave accurate record of variation of temperature. By the forward movement of the oscillating plate two dots are made at the same time,—one for the temperature and the other for the corresponding movement of the tree. As the two recorders do not move vertically up or down, but describe a circle, the dots vertically one above the other may not correspond as regards time. Any possibility of error in calculation is obviated by the fact that the thick dots in both the records are made every hour, and the subsequent thin dots at intervals of 15 minutes. Fig. 2. Apparatus for automatic record of movement of trees and plants; T, differential metallic thermometer; R, recording lever for temperature; R′, for recording plant movement; C, clock-work for oscillation of recording plate. The same clock-work moves plate laterally in 24 hours. A difficulty arose at the beginning in obtaining sanction of the proprietor to attach the recorder to the tree. He was apprehensive that its miraculous power might disappear by profane contact with foreign-looking instruments. His misgivings were removed on the assurance that the instrument was made in my laboratory in India, and that it would be attached to the tree by one of my assistants, who was the son of a priest. From results of observation it is found that the tree moves through its entire length; the fall of the highest point of the trunk is one metre. The movement is not passive, but an active force is exerted; the force necessary to counteract this movement is equivalent to the weight of 47 kilograms: in other words, the force is sufficient to lift a man off the ground. But far greater force would be required to restrain the change of curvature of the neck of the hard and rigid tree. 10 11 Fig. 3. Record of diurnal movement of the ‘Praying’ Palm (Phœnix dactylifera). Thermographic curve for 24 hours commencing at 9 in the evening is given in the upper record; the corresponding diurnal curve of movement of the tree is given in the lower. Successive dots at intervals of 15 minutes; thick dots at intervals of an hour. Before entering into the investigation of the cause of periodic movement I shall give a general account of its characteristics. A casual observation would lead one to conclude that the tree lifted itself at sunrise and prostrated at sunset. But continuous record obtained with my recorder attached to the upper part of the trunk shows that the tree was never at rest, but in a state of continuous movement, which underwent periodic reversals (Fig. 3). The tree attained its maximum erection at 7 in the morning, after which there is a rapid movement of fall. The down movement reached its maximum at 3-15 p.m., after which it was reversed and the tree erected itself to its greatest height at 7 next morning. This diurnal periodicity was maintained day after day. UNIVERSALITY OF TREE MOVEMENT. The next question which I wished to investigate was whether the movement of the particular Faridpur tree was a unique phenomenon. It appeared more likely that similar movement would, under careful observation, be detected in all trees. The particular palm tree was growing at a considerable inclination to the vertical; the movement of the tree and its leaves became easily noticeable, since the ground afforded a fixed and striking object of reference. In a tree growing more or less erect, the movement, if any, would escape notice, since such movements would be executed with only the empty space as the background. 12 Fig. 4. Record of the Sijbaria Palm from noon for 24 hours. Successive dots, at intervals of 15 minutes. Experiment 1.—Believing the phenomenon to be universal I experimented with a different Date Palm that was growing at my research station at Sijbaria on the Ganges, situated at a distance of about 200 miles from Faridpur. The surrounding conditions were very different. The tree was much younger; it was 2 metres in height and inclined 20° to the vertical. The curve obtained with this tree (Fig. 4) was very similar to that of the Faridpur Palm, though this extent to the movement was much reduced. The tree attained the highest erect position at 7-15 a.m. and the lowest at 3-45 p.m. Hence the movement of the Faridpur Palm is not a solitary phenomenon. THE CAUSE OF PERIODIC MOVEMENT. The recurrent daily movement of the tree must be due to some diurnal changes in the environment,—either the recurrent changes of light and darkness, or the diurnal changes of temperature. These changes synchronise to a certain extent; for, as the sun rises, light appears and the temperature begins to rise. It is therefore difficult to discriminate the effect of light from that of temperature. The only satisfactory method of discrimination would have been in the erection of a large structure with screens to cut off light. The effect of fluctuation of temperature under constant darkness would have demonstrated the effect of one agent without complication arising from the other. Unfortunately screening the tree was impracticable. I shall presently describe other experiments where the action of light was completely excluded. The curve of movement of the tree, however, affords us material for correct inference as regards the relative effects of light and temperature. The experiment was commenced in March; light appeared at about 5 a.m., the sunrise being at 6- 15 a.m.; the sun set at 6-15 p.m., and it became dark by 7 p.m. The incident light would be the most intense at about noon; after this it would decline continuously till night time. If the movement was due to light, its climax, either in up or down movement, would be reached at or about noon, and the opposite climax at midnight. But instead of this we find (Fig. 3) the up-movement reaching its highest point not at noon, but at 7 in the morning; after this the fall is rapid and continuous, and the lowest position was reached not in the evening but at 3-15 p.m. The fluctuation of light has, therefore, little to do with the movement of the tree. Turning next to the element of variation of temperature we are at once struck by the fact that the curve of movement of the tree is practically a replica of the thermographic curve (Fig. 3). The fall of temperature is seen to induce a rise in the tree and vice versâ. There is a lag in the turning points of the two curves; thus while temperature began to rise at 6 a.m., the tree did not begin to fall till 7 a.m. There is in this case a lag of an hour; but the latent period may, sometimes, be as long as three hours. The delay is due to two reasons; it must take some time for the thick trunk of the tree to attain the temperature of the surrounding, and secondly, the physiological inertia will delay the reaction. As a result of other in‐ vestigations, I find that the induced effect always lags behind the inducing cause. It is interesting in this connection to draw attention to the parallel phenomenon, which is described below, of lag in the variation of sensibility of Mimosa in response to variation of temperature. In this case the lag was found to be about three hours. Returning to the Palm, the tree continues to fall in the forenoon with rising temperature. At about 2-30 p.m. the temperature was at its maximum after which it began to decline; the movement of the tree was not reversed into erection till after 3-15 p.m., the lag being now 45 minutes nearly. I may state here that the movement of the tree is not primarily affected by the periodicity of day and night, but by variation of temperature. In spring and in early summer the rise of temperature during the early part of the day and the fall of the temperature from afternoon to next morning, are regular and continuous; the corresponding movements of the tree are also regular. But at other seasons, owing to the sudden change of direction of the wind, the fluctuations of temperature are irregular. Thus at night there may be a sudden rise, and in the earlier part of the day sudden fall of 13 14 15 temperature. And the record of movement of the tree is found to follow these fluctuations with astonishing fidelity, the rise of temperature being followed by a fall of the tree and vice versâ. That the movement is determined by the temperature variation is exhibited in a striking manner in Fig. 4, where, between 8 and 9 a.m., a common twitch will be noticed in the two curves. While trying to obtain some clue to the mysterious movement of the tree, my attention was strongly attracted by certain striking similarities which the record of the movement of the tree showed to the curve of the diurnal variation of moto- ex​cit​abil​ity, of the pulvinus of Mimosa pudica, an account of which will be found in a subsequent Paper of the series. PERIODIC MOVEMENT OF TREES AND DIURNAL VARIATION OF MOTO-EXCITABILITY IN MIMOSA PUDICA. The excitability of the main pulvinus of Mimosa pudica I find does not remain constant during the 24 hours, but undergoes a striking periodic change. At certain hours of the day, the excitability is at its maximum; at a different period it practically disappears. The period of insensibility is about 7 a.m., which, strangely enough, is also the time when the palm tree attains its maximum height. At about 3 in the afternoon the excitability of Mimosa reaches its climax, and this is the time when the head of the palm tree bends down to its lowest position. For the determination of the periodic variation of excitability of Mimosa I devised a special apparatus by which an electric stimulus of constant intensity was automatically applied to the plant every hour of the day and night, the responsive moment being recorded at the same time. The amplitude of responsive fall of leaf under uniform stimulus gave a measure of excitability of the leaf at any particular moment. In the lower curve of Fig. 5 is given the record of diurnal variation of excitability of Mimosa. Comparison of this figure with Figs. 3 and 4, will show the remarkable resemblance between the curves of diurnal movement of the Palm tree, and of diurnal variation of moto-ex​cit​abil​ity of Mimosa. The ex​cit​abil​ity of Mimosa reached its maximum at about 3 in the afternoon, when the Palm was at its lowest position. After this hour excitability fell continuously till 7 or 8 next morning. Corresponding to this is the continuous erection of the Palm from its lowest position at 3 p.m. to the highest between 7 and 8 a.m. Still more remarkable is the modifying influence of variation of temperature on the diurnal curve of excitability in Mimosa, and the diurnal curve of movement of the Palm. This will be quite evident from the inspection of the temperature curves in Figs. 4 and 5. Fig. 5. Curve of variation of moto-excitability of Mimosa pudica. The upper curve gives variation of temperature and the lower, the corresponding variation of ex​cit​abil​ity. I have shown elsewhere that the variation of moto-excitability of the pulvinus of Mimosa is a physiological function of temperature. The remarkable similarity between the diurnal variation of moto-excitability of Mimosa and diurnal movement of the Palm is due to the fact that both are determined by the physiological action of temperature. I shall presently describe experiments, which will establish the physiological character of the movement of the tree in response to changes of temperature. The records that have been given show that it is the diurnal variation of temperature, and not of light that is effective in inducing the periodic movement of the tree. Further experiments will be given in support of this conclusion. RELATIVE EFFECTS OF LIGHT AND TEMPERATURE. As regards the possibility of light exerting any marked influence on the movement of the Palm tree, I have shown from study of time-relations of the movement, that this could not be the case. Moreover, it is impossible for light to reach the living tissue through the thick layer of bark that surrounds the tree. That the effect of light is negligible will appear from 15 [A] 16 17 [B] 18 the accounts of following experiments, where the possibility of the effect of changing intensity of light is excluded by maintaining the plant in constant darkness, or in constant light. The employment of the large Palm was obviously impracticable in these investigations. I, therefore, searched for other plant-organs in which the movement under variation of temperature was similar to that of the Date Palm. I found that the horizontally spread leaves of vigorous specimens of Arenga saccharifera growing in a flower pot executed movements which were practically the same as that of the Faridpur tree. The leaf moved downwards with rise of temperature and vice versâ. There are many practical advantages in working with a small specimen. It can easily be placed under glass cover or taken to a glass house, thus completely eliminating the troublesome disturbance caused by the wind. Diurnal movement in continued darkness: Experiment 2.—The plant was placed in a dark room and records taken continuously for three days. These did not differ in any way from the normal records taken in a glass house under daily variation of light and darkness. Exposure of plant to darkness for the very prolonged period of a week or more, undoubtedly interferes with the healthy photo-tonic condition of the plant. But such unhealthy condition did not make its appearance in the first few days. PHYSIOLOGICAL CHARACTER OF THE MOVEMENT. There may be a misgiving that the movement of the tree might be due to physical effect of temperature. If the upper strip of a differential thermometer be made of the more expansible brass and the lower of iron, the compound strip bends down with the rise of temperature. Similarly the movement of the tree might be due to the upper half being physically more expansible. It would have been possible to discriminate the physical from the physiological action by causing the death of the tree; in that case physical movement would have persisted, while the physiological action would have disappeared. As this test was not practicable, I tried the effect of physiological depression on the periodic movement of the leaf of Arenga saccharifera. Fig. 6. Effect of physiological depression on diurnal movement of the petiole o f Arenga saccharifera. The uppermost curve exhibits variation of temperature, (a), normal diurnal curve, (b), modification after 3 days’ and (c) after 7 days’ withholding of water. Effect of Drought: Experiment 3.—In Fig. 6 is given a series of records of movement of the leaf-stalk of Arenga, first under normal condition, afterwards under increasing drought, brought about by withholding water. The uppermost is the thermographic record which remained practically the same for successive days. Below this are records of movement of the leaf (a) under normal condition, (b) after withholding water for three days, and (c) after deprivation for seven days. It will be noticed how the extent of movement is diminished under increasing physiological depression brought on by drought. On the seventh day, the responsive movement disappeared, there being now a mere fall of the leaf, which was slow and continuous. After this I supplied the plant with water and the periodic movement was in consequence nearly restored to its original vigour. 19 Effect of poison: Experiment 4.—In another experiment the normal diurnal record with the leaf was taken and the plant was afterwards killed by application of poisonous solution of potassium cyanide. The diurnal movement was found permanently abolished at the death of the plant. These experiments conclusively prove that the periodic movement of the leaf-stalk induced by variation of temperature is a physiological phenomenon, and from analogy we are justified in drawing the inference that the movement of the Faridpur tree is also physiological. The question, however, was finally settled by the unfortunate death of the tree which occurred the other day, nearly a year after I commenced my in​ves​ti​ga​tions. While presiding at my lecture on the subject, His Excellency Lord Ronaldshay, the Governor of Bengal, announced that a telegram had just reached him from his officer at Faridpur that “the palm tree was dead, and that its movements had ceased.” Since my investigation with the Faridpur ‘Praying’ Palm, I have received information regarding other Palms, which exhibit movements equally striking. One of the trees is growing by the side of a tank, the trunk of the tree being inclined towards it. The up-lifted leaves of this tree are swung round in the afternoon and dipped into the water of the tank. The movement of the tree has been shown to be brought about by the physiological action of temperature variation; in other words the diurnal movement of the ‘Praying’ Palm is a thermonastic phenomenon. I have found various creeping stems, branches and leaves of many trees, exhibit this particular movement of fall with a rise of temperature, and vice versâ. Such movements, I shall, for the sake of convenience, distinguish as belonging to the negative type. Having found that the temperature is the modifying cause, the next point of inquiry relates to the discovery of the force, whose varying effects under changing temperature induces the periodic movement. I shall, in this connection, first discuss the various tentative theories that may be advanced in explanation of the movement. TRANSPIRATION AND DIURNAL MOVEMENT. It may be thought that the fall of the tree during rise of temperature may be due to passive yielding of the tree to its weight, there being increased transpiration and general loss of turgor at high temperature. I shall, however, show that the diurnal movement persists in the absence of transpiration. Diurnal movement in absence of transpiration: Experiment 5.—In the leaf of Arenga saccharifera, I found that the petiole was the organ of movement. I cut off the transpiring lamina and covered the cut end with collodion flexile. The plant was now placed in a chamber saturated with moisture. The petiole continued to give records of its diurnal movement in every way similar to the record of the intact leaf. In another experiment with the water plant, Ipoemia reptans, immersed in water, the normal diurnal movement was given by the plant, where there could be no question of variation of turgor due to transpiration. (See also Expt. 7.) In the diurnal movement of the ‘Praying’ Palm the concave curvature of the rigid neck in the morning, became flattened or slightly convex in the afternoon. The force necessary to cause this is enormously great, and could on no account result from the passive yielding to the weight of the upper part of the tree. From the facts given above it will be seen that the diurnal movement is not brought about by variation in transpiration. I now turn to another phenomenon which appeared at first to have some connection with the movement of the tree. Kraus found that the tissue tensions of a shoot exhibit a daily periodicity. He, however, found that between 10°C. and 30°C., variation of temperature had no effect on the daily period. But as regards the diurnal movement of the tree, it is the temperature which is the principal factor. Kraus also found a daily variation of bulk in different plant-organs; this variation of bulk is connected with transpiration, for the removal of the transpiring leaves arrested this variation. But the periodic movement of the tree, as we have seen, is independent of transpiration. Millardet observed a daily periodicity of tension in Mimosa pudica. He found that maximum tension occurs before dawn; the petiole becomes erected, the movement being upwards or towards the tip of the stem. Tension decreases during the day, and reaches a minimum early in the evening; in correspondence with this is the fall of the petiole, the movement being away from the tip of the stem. If the plant were placed upside down the periodic movement of the petiole in relation to the stem will evidently remain the same, but become reversed in space. Maximum tension in the morning will make the petiole approach the tip of the stem, i.e., the movement will be downwards instead of upwards as in the normal position. The experiment described below will show that the diurnal movement induced by variation of temperature is not reversed by placing the plant in an inverted position. Diurnal movement in inverted position: Experiment 6.—I took a vigorous specimen of Arenga saccharifera growing in a pot, and took its normal record, which as explained before exhibited down-movement during rise, and an up-movement during fall of temperature. The plant was now held inverted, the upper side of the petiole now facing the earth. The diurnal curve of movement should now show an inversion, if that movement was solely determined by the anisotropy of the organ. But the record did not exhibit any such inversion. After being placed upside down, the leaf did not, on the first day, show any diurnal movement; there was, on the other hand, a continuous down-movement on account of the fall of the leaf by its own weight. But in the course of 24 hours the leaf readjusted itself to its unaccustomed position, and became somewhat erected under the action of geotropic stimulus. After the attainment of this new state of geotropic equilibrium, the leaf gave a very pronounced record of its diurnal movement which did not show any reversal; the inverted leaf continued to exhibit the same characteristic movements as in the normal position, that is to say, a down movement during rise, and an up-movement during fall of temperature. As the plant in the inverted position did not show any reversal of the periodic curve, it is clear that the diurnal movement is determined by the 20 21 22 23 [C] 24