The Motor Mechanism of Plants

Effect of amputation of upper half of pulvinus Curves showing differential excitability of upper and lower half of pulvinus of Mimosa . . . . . . .. Responses of a subtonic specimen of Mimosa Effect of the application of KC1 solution on the pulvinus . Record of iatent period of Mimosa with a 200-vibration recorder Additive effect of stimulus of intensity o*5 .... Different phases in the fatigue-reversal in Mimosa Positive, diphasic, and negative response in. a subtonic specimen of Mimosa . . . . . *1 .

Staircase increase in successive responses of subtonic Mimosa Staircase response followed by fatigue in Mimosa . Preliminary staircase followed by fatigue in tlie response of e Frog’s muscle . . . f . . Longitudinal section of petiole and pulvinus of Mimosa Reproduction of phofes-micrographs of portions of the pulvini of Active' Mimosa, semi-active Neptunia, and inactive Berm-plant- ......... Transverse sections of pectoral muscles of the falcon, the goose, and the domestic fowl . . . . '

38. Impressing efiedt of a passing cloud on the response of Mimosa 39, Abolition of ^moto -excitability of pulvinus of Mimosa by Total abolition of excitability and death of plant (Mimosa) Effect of ether (Mimosa) ...... The petiole-pulvinus preparation attached to the Resonant, Recorder . # . 49. The effect of wound on detached shoot Stimulating action of light, and depressing action of darkness Incomplete recovery under fhe action of BaCl2 • Antagonistic action of acid and alkali .

determination of the diurnal variation of excitability Effect of moderate cooling in depressing excitability Effect of exposure to intense cold . . . 57. Record for 2 4 hours, exhibiting diurnal variation of excitability Midday record from noon to 3 P.M., exhibiting uniform and c The gradual waking up of the plant from 8 a.m. to 12 n<: on . Curve of variation of moto-excit ability of Mirtosa pudica Diurnal variation of moto-excitability exhibited by summer- specimen (Mimosa) . . . . . . . .

Record of diurnal variation of excitability of specimen which exhibited marked nyctitropic movement (Mimosa) Commutator, for causing make and break of electric current 72. Stimulating action of Camphor on puhinar respon;e (Mimosa) 73. Stimulating action of Camphor on response of Frog’s muscle 77. Effect of minute dose of Strychnine in enhancing the con¬ 78. Diagrammatic representation of the measurement of diametric 81. Record of diametric contraction of pulvinus of Mimosa . .

82. Record of diametric contraction of cortex of stem of Mimosa. 84. Response of ordinary leaf under transmitted excitation of 88. Res^ onse of the stem of Phaseolus to unilateral stimulation . 90. Response of geotropically curved organ under diffuse electric 91* Response of the Mimosa pulvinus to irrigation and to with¬ drawal of water . . . . . . . 94. Responses of stem, leaf -joint, and pulvinus of Mimosa to 95. Method of obtaining electric response of the pulvinus of Mimosa

t 01 . Increasing amplitude of electric response to increasing tor¬ sional stimulation ........ 102. Uniform electric responses under torsional stimulation . 103. Fatigue of electric response with shortened -period of rest 104. Abolition of electric resporse by steam .... X05. Gradual abolition of electric response under chloroform too. Arrangement for obtaining electric response of the leaf to light 107. Effect of in creasing duration of exposure of 5, 10, and ^seconds

Experimental method for obtaining response to mechanical stimulation by resistivity variation . . . . . Recced showing uniform responses to mechanical stimulation Effec t of C‘ loroform in inducing depression of response by variation of resistance . . . . . Method of resistance-variation in response to stimulation . Effect of electric stimulation of moderate intensity Effect of feeble electric stimulation . . . . . The Quadrant Method for determination of variation of electric resistance under photic stimulation Equal responses in opposite directions on alternate illumina¬ tion of the two pairs of quadrants (Tropaeolum) . . .

Abolition of response to warming or codling in specimen which had passed the death-point . . . . . . Therm.o-mer.hanical curve indicating death-point at 6o° C. of leaf of Bean (Phaseolus) ...... Determination of death-point of pulvinoid (Eichhornia) . Death-spasm of the geotropically curved stem of Baseila alba Determination of the death-point by electromotive variation Multiple response to transmitted death-excitation at 6o°C. (Averrhoa) Multiple response of leaflet of Biophytum imder transmitted death-excitation due to poisoning . . . .

The Balance for recording apparent variation in weight at death Record of variation in weight of Carissa fruit at death under rise of temperature . . . . . U-tube support for the leaf, and the plant-chamber Photograph of the Oscillating Recorder . . . . . Continuous record of pulsation of Desmodium leaflet for 4 hours Record of a single pulsation of Desmodium .... Gradual stoppage of pulsation in isolated leaflet 01 Desmodium Response of Desmodium leaflefin a state of standstill . .

Prolonged revival of pulsation under moderate electric stimula¬ tion .......... Multiple response in Biophytum to a moderately strong electric shock . . . * . . * . Multiple response ir Biophytum ..... Response of Biophytum leaf to stimulation!, of varying duration . ... . 1 ... . Single response of Desmodium leaflet ..... Stimulus applied at systolic and diastolic phase 'Frog) . . Extra pulsation of Desmodium under stimulation at diast le. The Resonant Cardiograph . . . . . . .

Irregular record of heart-beat of Frog due to lricticn . Characteristic cardiograms of Tortoise, Frog, air’ Fish . . Diagrammatic representation of Recorder for the pulvinule of Desmodium . . . . . . . . . Effects of drought and irrigation on pulsation of Desmodium Effects of oxygen and carbonic acid g~s in reviving and arresting pulsation of Desmodium leaflet . . . . Arrest of normal heart-beat of Frog under the action of 0O2 . Revival of Frog’s heart-beat by feeble and by strong electric stimulation . . . . . . ...

The feeble automatic pulsation iu dark enhanced after stimulation by light Transmitted effect of moderate and indirect electric stimulation Effect of cooling in ariest 'ng the pulsatory activity . . . Effect of rise of temperature in increasing frequency of pulsation (Desmodium) ....... Effect of rise of temperature in enhancement of frequency of Stimulating action of Spirit. Ammon. Arom. on heart-beat of Frog ......... Action of a minute dose and of a larger dose of KB*- on Desmodium pulsation ......

Oppc ,ite effects of minute and strong doses of KBr on heart¬ beat (Frog) . Antagonistic action of Muscarin and Atropin Antagonistic action of Piiocarpin and Atropin . Revival of depressed activity of Desmodium by A^roma Parallel effects on pulsating activity of Frog’s heart . . Uniform automatic pulsations of Frog's stomach Arrested pulsation of stomach due to lack of oxygen Effect of C02 on normal pulsation of Frog's stomach . Effect of variation of temperature on pulsation of Frog’s stomach

Responses to mechanical stimulation (Prog’s stomach) Response^ to eleQtric stimulation . . . ' . Effect of continuous chemical stimulation with Cholin Chlorate Effect of unilateral thermal stimulation .... Eafect of poisonous and <*f stimulating solutions on shoots Effect of poisonous solution in diminishing the rate of suction * The Applicator for applying different solutions at cut end of Effect of stimulus of light in enhancing the activity of ascent 'She arrested activity of ascent revived by electric stimulation . Effect of alternate application of cold in depressing and heat in enhancing rate of ascent of sap Alternate arrest and enhancement of ascent of sap by depress¬ ant and stimulant ........

Uniform sphygmograms of young stem of Leucosceptrum Dee Effect of variation of temperature on propulsive activity . Diagram of passage pf hydraulic wave from cut end of stem to leaf above ......... Sphygmograms of descending and ascending hydraulic waves in a bare varnished stem ....... Diurnal variation of pressure in leafless tree ... Method for record of electric pulsation of pulvinule of Des- Simultaneous record of mechanical pulsation and corresponding electric pulsation of pulvinule of Desmodium The Electric Probe for the localisation of the pulsating tissue in the stern . « .« . . « . . . .

Record showing the amplitude of electric pulsation '^different layers of the stem of Impatiens ..... Electric connexions for record of electric pulsation of the Effect of stimulus of light enhancing electric pulsation in a Curves showing rates of suction in varnished stems of Centaurea and Impatiens . . . ; Curves shdwv.ng the effect on transport on sap in a stem when watef is applied at. either end . . . . . . Diagrammatic representation of the Potograph and of the effects induced Tiy stimulation or depression

Directive flow of sap under differential iniulation ; L besa! end and apical end of the petiole . . . . • • 35^ Effect on pulsation of alternate drought and supply of '.atei 3O0 Effect of application of warm water in increasing sap-pr^ sure in a shoot * . . . . • . • • • 3^3 Effect of feeble indirect stimulation in enhancing the sap- pressure . . . . . . . * • • 37Q Effect of dilute solution of Camphor on heart-beat of Prog . 373 Effect of Camphor in enhancing the sap-pressure by increasing the pumping activity . . . . . . 374

Antagonistic action of Musk and Bromide of Potassium on heart-beat of Frog . . . — . . . . 370 Effect of KBr in depressing and of Musk in enhanci. g sap- pressure (Impatiens) ..... A . 377 Effect of Morphine anu Atropine on heart-beat of Frog . . 378 Effect of dilute Strychnine in stimulating the heart-beat of Frog 37S Action of Strychnine on the plant ..... 379 Effects of thermal stimulation or depression on movement of sap in sealed stem . . . . . . . . 382

Record of transmitted effects of electric stimulation . . . 389 Diagrammatic representation of effects of chemical stimulant- end depressant ........ 391 Record of opposite effects on pressure and movement of sap of Camphor and KJ3r ... .... 392 Diagram of effect of thermal stimulation and depression . . 398 Record of effects of alternate thermal stimulation and depression . 400 Movement is a characteristic property of living organisms. It may be locomotb’ry, as when the whole organism moves ; or a parr of the organism may move, whilst as a whole it. remains in the same place.. It is probable that the original living organisms were locomotory, swimming in the sea, and from these have been evolved the animal series which are typically motile, and the plant series which are as typically sessile.

I 'he original unicellular living organisms consisted, as do many at present, of nothing but a speck of living proto¬ plasm. Motility, that is the capacity of effecting changes of form or position which we call movement, ic an inherent property of protoplasm. This is the starting-point of any possible consideration of the mechanism o^ movement. The primitive mechanism has been observed to be this : (u) that after stimulation the protoplasm reduces the whole or some part.of its bulk ; this has beeir termed ‘ contraction/ and protoplasm is, therefore, said to be ‘ contractile ’ ; and (b) that after contraction the protoplasm recovers its previous bulk, contraction being* followed by expansion. The general expression contractility of protoplasm ’ includes both contraction and expansion.

It appears from what has just been said that any move¬ ment of the protoplasm is the result of a previous stimulation, that is, of a disturbance of its equilibrium by some external agent, vdrich is the ‘ stimulus/ such as a touch, an electric shock, a sudden variation of temperature or of light. Inas¬ much as it responds to the action of a stimulus, the proto¬ plasm is descrioed as being irritable/ or 4 excitable, or sometimes 4 sensitive/ In the simple unicellular organism the whole of the protoplasm is equally contractile and irritable. In the course of evolution, as more and more complex organisms were developed, attaining various degrees of physiological differentiation, the contractile and the irritable functions have come to be more or less concentrated in certain parts of the body and in certain specialised tissues : contractility in the motor organs, and in the contractile tissue termed 4 muscle ' in the animal ; irritability in the sensory organs receiving and those conducting excitation, and in the tissue termed “nerve.^ But this segregation of function is not absolute. It is most complete in the case of nerve which responds to stimulation without any contraction or other visible indication of its activity : muscle, on the oilier hand, is both irritable and contractile. In virtue of this combination of properties, conveniently termed 4 rheto- excitability/ the excitability of muscle is mechanically manifested by its contractile response to stimulation, excitability of nerve, apart from muscle, can only be detected by the electric variation wThich it, in common with all the living tissues of the body, undergoes when stimulated, a method which involves the use of the galvanometer.

The differentiation of the tissues has never reached in the plant series anything like the same degree as in the animal series ; this is especially true of the motile or con¬ tractile tissue, as well of the associated nervous tissue. Hence it is only In a genera1 sense that it is possible to 'apply the term 4 muscle ' and 4 nerve J to the contractile and the excitatory tissues of plants. It is not surprising that these tissues should be so highly developed in the locomotory animal, and should be hss developed in the sessile plant. Nevertheless I shall be able to show that in the plant the motile organ has reached a degree of complexity, hitherto unsuspected, containing as it does contract' ie tissue which may well be called *’ muscle * anil conducting tissue which may well be called f nerve/

In all but the simplest plants the body is an aggregate of units of protoplasm known as cells, each enclosed in a non- protoplasmic wall. The bulk of the living tissue of the plant is made up o* such cells. The cell-wall consists of what may be summarily described as cellulose, witnin which is the living protoplasm closely lining the wall at all points. Except in quite young cells the protoplasm does not fill the whole cavity of the ceil ; it adheres to the wall throughout, forming a thin living membrane. The cavity enclosed within this living membrane is the vacuole, filled with the watery cell -sap holding various substances, such as acias, salts, sugar, colouring matters, etc., in solution. It is by such cells as these that the movements of the various parts of the plant-body are effected.

What are the movements that the plant performs ? All plants and all parts of ihem, at a certain stage of develop¬ ment perform the slow automatic movement known as growth/ This movement can only be effected by young cells and is, therefore, a merely temporary feature in the life of an ordinary tissue-cell. But in certain plants, commonly termed * sensitive plants/ there are groups of cells, situated in special motile organs, which not only retain their power of movement but possess it in an increased degree after th*wr have attained their adult development, and constitute characteristic contractile tissue. The movements, chiefly of the leaves, that these organs effect are not spontaneous, as is growth, but are induced by a stimulus acting from without. It is on this account that the plants manifesting these movements have been described as 4 sensitive/ Their motile organs* present various grades oT both motility and

sensitiveness : some respond with a prompt and active movement to but a slight stimulus', whereas others respond but sluggishly to even, a fairly strong stimulus. ' What, now, is the ultimate mechanism of the individual contractile cell . What is its condition preliminary to con¬ traction ? The first essential is that it should be in good tonic condition, arid this is true of all active living cells. What, exactly, are the factors in the state of ‘ tonus ’ is not clear, but they must include the excitability that enables the protoplasm to respond to stimulation ; and, further, a store of -latent energy necessary for the work, whatever it may be — iii this case it is contraction — which the cell has to perform. Its mechanical condition is that it is in a state of internal s tension, generally termed ‘ turgor/ like an inflated football ; the vacuole contains as much sap as it can hold I he elastic cell-wall is stretched to its utmost ; but, as it is Readily permeable, there must be some structure which prevents the escape of liquid under pressure from the cell. The structure in question is the lining layer of proto¬ plasm, which is a semi-permeable membrane allowing the entrance of water but resisting the escape of the cell-sap. The accumulation of water in the vacuole is the effect o: the osmotic action of substances dissolved in the cell- sap. When a stimulus acts upon the turgid contractile cell, the result is that the cell as a whole shrinks, cell-sap escapes through the protoplasmic lining, and the cell loses its turgidity. On the cessation of stimulation, recovery of the previous condition of the cell begins with reabsorption of water, and ends in the restoration of turgor.

How are these events to be interpreted ? i hey have been interpreted in various ways which need not be dis¬ cussed here. It must suffice to. sav that, as the protoplasm has inherent motility, and is known to be sensitive to the action of stimuli, it is the chief factor in maintaining or producing variation of the turgidity of the cell. In response +o a stimulus it ‘ contracts,’ a process which must be associated with a sudden increase of its permeability sc as

to permit the escape of liquid from the ceil with resulting diminution of turgidlty. It must be admitted that our present knowledge of the contraction cf protoplasm under stimulation is not complete as to the minutiae of the processes by which it is brought about. In muscle it is oupposed that during the act of contraction there is a transfer and redistribution of fluid material.1 In both plant and animal there is thus a fundamental protoplasmic reaction which finds external expression in a movement. Whether or not this reaction is essentially similar in the two cases can only be decided by comparing the records of their responses under all possible variations of external conditions.

Mention should be made of the special case of auto- maticaHy pulsating tissue. An ordinary muscle undergoes contraction only in response to the action of an external stimulus ; but there are other muscular tissues which con- tract repeatedly with a rhythmic pulsation. A familiar instance of this is afforded by the rhythmic movements ol the leadets of the Telegraph Plant, Desmodium gyrans. It is seen in its highest perfection in the animal heart, the rapid rhythmic peristaltic activity of which maintains the pro¬ pulsion of the blood, a functional activity which has hitherto been unsuspected in the plant. I will in the present work give a more detailed account of the discovery of a rhythmic propulsive mechanism in the plant analogous to that of the animal heart.

ihere remains further the consideration of the relation of movement to external conditions ; for instance, how an electrical current, or heat or light, or chemical substances, or the various changes, in the environment, affect the response given by the excitable and contractile cells. 1 Schafer, working on the highly differentiated wing-muscle of the \va;>p, concludes fhat each sarcomere contains a darker substance near the centre, divided into two parts by Hensen’s disc. At each end of the sarcomere the contents are clear and hyaline". In the act of contraction the clear material flows, according to Schafer, into tubular pores, in the central dark material.’ — Stalling, Elements of Human Physiology , Eighth Edition, p. 91.