Researches on Irritability of Plants

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I HAVE in this work dealing with my researches on the irritability of plants introduced new methods by which the scope of investigation has been enlarged, and a very high degree of accuracy secured. In my previous treatise on Plant Response, the response recorder employed was a modification of the optical lever, automatic records being secured by the very inconvenient and tedious process of photography. The delay thus imposed retarded seriously the progress of the research. Those practically engaged in investigations on plants can realise the difficulties that arise from the too quick passage of the seasons. It thus frequently happened that by the time new instrumental appliances were rendered practicable the favourable season for the plant was over, involving the postponement of the experiment for another year. In spite of these difficulties, the long series of investigations that I then carried out gave many interesting results, which not only threw light on many obscure problems, but also led to the discovery of several important phenomena in plant physiology.

Some of these results, moreover, tended to cast doubt on certain conclusions that had found universal acceptance. It has, for example, been held that there was no trans- mission of true excitation in Mimosa, the propagated impulse being regarded as merely hydro-mechanical. The question whether the transmitted impulse was physical or physiological could only be satisfactorily decided if the plant could itself be made to record the velocity of its impulse and the changes induced in that velocity under

ideal methods of attacking problems in the life of plants, the realisation of which would make a great advance in physiological investigation. It would also be desirable to discard, if possible,” the troublesome method of obtaining record by photography, which necessitates work in a dark room ; in this connection it should be remembered that subjection of the plant to darkness introduces complications by modifying its normal excitability. For these reasons, another requirement which it is necessary to fulfil is the devising of some simple and direct method of obtaining the record. And in order that the results obtained should not be influenced by any personal factor, it would be further desirable that the plant attached to the recording apparatus should be automatically excited by stimulus absolutely constant, should make its own responsive record, going through its own period of recovery, and embarking on the same cycle over again without assistance at any point on the part of the observer.

The difficulties encountered in realising these ideal requirements appeared at first to be insurmountable. In the records of response serious errors occurred as regards ampli- tude and time-relations, owing to the friction of the writing lever against the recording surface. Asan extreme instance of this, in recording the rhythmic movement of the leaflets of Desmodium the very slight friction which the smoked- glass surface offered was enough to stop the pulse-record.

After many attempts, I was at last successful in overcoming all obstacles by the device of the Resonant and Oscillating Recorders. Taking the very difficult test of direct record of the rhythmic movements of Desmodium leaflets, it will be found that the pulsations recorded in this book not only gave accurate measure of the amplitude and period, but also the absolute rate of movement during any phase of their autonomous response. Again, in the matter of accurate measurement of short intervals of time required for the determination of the latent period and velocity of transmission of excitation, I have shown the possibility

of recording time-intervals as short as a thousandth part of a second. A brief account of this is given in my paper “On an Automatic Method for the Investigation of the Velocity of Transmission of Excitation in Mimosa,” read before the Royal Society. It will be recognised immediately in how many directions our power of inquiry has become extended by the elaboration of these new methods and the invention of several types of instrumental appliances described in this work.

In presenting the results of these investigations, it will be noted that the plant has been made to tell its own story, by means of its self-made records. Each experiment has been repeated at least a dozen times, in many cases as often as a hundred times. The results may therefore be accepted as fully attested. The establishment of the unity of re- sponsive reactions in the plant and animal, which is the subject of this work, will be found highly significant, since it is only by the study of the simpler phenomena of irritability in the vegetal organisms that we can ever expect to elucidate the more complex physiological reactions in the animal tissues.

I take this opportunity to thank my research assistants, Messrs. Guruprasanna Das, L.M.S., and Surendra Chandra Das, M.A., for the very efficient help rendered by them in these researches. Action of environment on plant—Revelation of internal condition by character of response—Problems to be solved—Electrical response—Mechanical response—Motile organ in Mimosa pudica—Response in plant and animal—Different phases of the responsive movement—Graphic record—Determination of absolute movement of leaf and its time-relations— Characteristic effects of different agencies on the response- curve—Specific difficulties in recording plant-response : I

Advantages of intermittent contact in record—Two types of apparatus: the Oscillating Recorder, and the Resonant Recorder—Coercer and Vibrator—Perfect tuning—Recorders with standardised frequencies—Slide and clockwork—The record its own chronogram—Smoked surface and its fixation— Adjustments of the writer—Records with continuous and intermittent contacts c : : : : : : II Different methods of stimulating the plant: mechanical, chemical, thermal and electrical—Difficulties of securing quantitative stimuli—Direct and indirect stimulation—Ideal modes of stimulation—Electro-thermic stimulation—Stimulation by constant current—Stimulation by condenser-discharge—Non- polarisable electrodes—Direct, extra-electrodal, and intra- electrodal stimulation—Stimulation by induction-shock— Effects of make- and break-shock—Excitation by tetanising shock . : . P 5 : : . ;

Latent period of Mimosa—Apex time—-Rate of responsive move- ment of leaf—Effect of intensity of stimulus, fatigue, and temperature—Periodic dot marker—Time relations of response and recovery—Effect of season—Response of Biophytum— Response of Neptunia—Abitrary distinction between sensi- tive and ordinary plants—Differential response in Mimosa— Response of ordinary plants—Universal sensitiveness of plants—Standardisation of stimulus—Maximal and Minimal Stimuli— Extreme sensitiveness of Mimosa . : 5 3 35

Greater excitatory efficiency of the break-shock—Additive effect of stimulus—Quantitative relation of additive effect—Effect of load—Thermal chamber—Effect of temperature—Effect of increasing intensity of stimulus on response c : - 52 Necessity of uniform stimulation—The Periodic Starter—The Automatic Exciter—Electrolytic contact-maker—The com- plete Response-recorder—The factor of tonicity—Uniform responses—Fatigue under shortened period of rest—Growing fatigue—Alternating fatigue—Staircase response—Explana- tion of erection of leaf under continuous stimulation—Fatigue- relaxation in plant and animal—Response under single stimulus and under tetanisation . d : . : : 64

Induced change of excitability under sudden variation of light— Abolition of excitability by absorption of water—Restoration of excitability by application of glycerine—Stimulating, depressing, and toxic agents—Phenomenon of accommodation —Stimulating action of ozone—Effects of carbonic-acid gas, vapour of alcohol, ether, carbon disulphide, coal gas, chloroform, ammonia, sulphuretted hydrogen, laughing-gas, nitrogen dioxide, and sulphur dioxide . - . . : 85

Criterion of the death of plant—Abolition of electric response at death—Mechanical spasm of death—Water-bath for uniform rise of temperature—Excitatory effect of sudden cooling or heating—Erection of leaf with rising, and depression of leaf with falling, temperature—Thermo-mechanical inversion at the death-point—Necessity for specification of rate of rise of temperature —Death-record of Mimosa — Abolition of response after death-spasm—Constancy of death-point exhibited by different specimens— Death-records of Desmodium gyrans and Vicia Fava—Death-spasm in ordinary plants—The electric-spasm of death—Lowering of death- point by fatigue and by poisonous solution . é , ‘ 98

Difficulties of accurate determination of Latent Peviod—Advan- tages of Resonant Recorder—Simultaneous tracings of tuning- fork exciter and Resonant Recorder—Automatic stimulation at a definite moment—Identical value of latent period in successive determinations—Accurate measurement of time- interval shorter than .oo5 second—Latent period little affected by inertia of recorder—Tabular statement of value of different specimens of Mimosa—Effect of season on latent period . 108

Diffuse stimulation under alternating-shock—Effect of intensity of stimulus on Latent Period—Influence of optimum condition —Effect of fatigue—Effect of temperature . : - 5 122 Detection of transmitted excitation by means of electromotive variation—Specific tissue for conduction of excitation—Hydro- mechanical theory of transmission of stimulus—Propagation of excitatory protoplasmic change—Physiological test—Auto- matic record of transmission-period—Conditions for obtaining constant velocity—Determination of velocity of transmission in Mimosa—Differential method of determining velocity— Constancy of results—Tabular statement of different deter- minations of velocity—Effect of intensity of stimulus on velocity of transmission—Effects on sub-tonic tissue and on tissue in optimum condition—After-effect of stimulus in enhancing conductivity—Effect of optimum condition— Disturbing action of leakage of exciting current—Effect of fatigue—Effect of temperature—Velocity of transmission in Biophytum and Averrhoa—Direction of preferential conduction 132

The hydro-mechanical theory—lInconclusive character of the anesthetic experiment of Pfeffer and scalding experiment of Haberlandt—Kiihne’s experiment showing transmission of excitation under intense stimulation in a rigored nerve— Error introduced by employment of excessive intensities of stimulus—Discriminative polar effect of current in excitation —Block of transmission of excitation by local application of cold—Restoration of normal conductivity by tetanising shock in tissue paralysed by cold—Electro tonic arrest of excitatory impulse—Action of various poisons in inducing block of con- duction . ; : : : : A ; : : 154

Two opposite kinds of responses, negative and positive—Excitatory contraction, negative turgidity variation, fall of leaf, and concomitant negative electric variation—Positive electric response—Positive or erectile mechanical response—Dual impulses under different forms of stimuli—Exhibition of positive and negative impulses by different plants—Con- ditions for obtaining positive response—Characteristics of positive impulse—Masking and unmasking of positive effect—

Polar excitation in animal tissues—Anomalous reactions in Pro- tozoa—Mono-polar method—Current Reverser—Excitatory polar action in plant—Method of record—Effects of ascending and descending currents in animal and plant—Records giving time-relations—Potential slide—Measurement of E.M.F. and current—Potential keyboard Polar effects of feeble and moderate currents on (1) leaflets of Mimosa, (2) leaflets of Biophytum, (3) leaflets of Neptunza, (4) leaflets of Avervrhoa carambola, (5) leaflets of Averrhoa bilimbi, and (6) primary leaf of Mzmosa—Excitation with feeble current only at kathode-make—Excitation at kathode- make and anode-break, under moderate current—Tabular statement of results .

Polar effects of currents on pulsation of Desmodium gyvans— Reduction of systolic contraction by anodic action—Diminu- tion of diastolic expansion by kathodic action—Arrest at systole by make of kathode and diastolic expansion by break of kathode—Arrest at diastole by make of anode, and systolic contraction by break of anode—Effects of ascending and descending currents of feeble and strong intensity in nerve- and-muscle preparation—Parallel effects in petiole-and-pul-

Excitability of nerve to induction-shock diminished by cooling— Nerve excitation by constant current enhanced by cooling— Excitation of conducting-tissue of Mimosa by constant current enhanced by cooling and depressed by warming— Ineffective stimulus becoming effective under cooling and vice versa — Multiple response induced in Biophytum by the passage of constant current—Comparison of sensitiveness of plant and animal—Minimum current for excitation of human tongue—Relatively higher sensitiveness of Biophytum .

Abnormal polar reactions in Pyotozoa—Transformation of polar reaction in leaf of Mimosa from Type II. to Type III. under strong current—Further transformation to Type IV. under stronger current—Exhibition of Type III. and Type IV. by leaflets of Mimosa, Biophytum, Averrhoa carambcla—Law of polar action of strong currents Modification of polar reaction under tissue-changes—Effect of age—After-effect of moderate stimulation—Modified polar effect; excitation at kathode-make and anode-make; excita- tion at kathode-make, kathode-break, and anode-make— General review of polar reactions

Oscillating Recorder—Latent period of Biophytum—Refrac- tory period—Response on ‘ all-or-none’ principle—Multiple electrical response to a single strong stimulus—Multiple mechanical response to strong stimulus in Biophytum and Averrhoa—Continuity of multiple and automatic response— Ordinarily responding Biophytum converted into automatically responding condition by excess of stored energy—Automati- cally responding Desmodium converted to ordinarily respond- ing condition by depletion of stored energy

Activity of detached leaflet of Desmodium—Pulsation maintained uniform under constant internal hydrostatic pressure—The plant-chamber—Time-relations of pulsating movement derived from dotted record—Significance of down and up movements —Systole and diastole—Table showing rates of movement of Desmodium leaflet at different phases : : : 7 200 Effect of internal hydrostatic pressure on the pulsation of Desmo- dium—Expansive erection of leaflet under increased pressure ; diminution of the extent of systolic contraction—Effect of load: diminution of period—Stannius’ ligature on heart-beat —FParallel effect of ligature on pulsation of Desmodium—

Arrest of pulsation by a cut and revival by electric shock : 300 Condition of standstill brought about by depletion of energy— Renewal of pulsation by the stimulus of light—Response to stimulus of induction-shock—Multiple response under tetani- sation—Determination of the latent period and the apex time —Refractory period—Effect of stimulus on leaflets in sub- tonic condition—Fffect of isolation on rhythmic activity— Gradual arrest of pulsation resulting from run-down of stored energy—Effect of fresh accession of energy - . 3 306

Effect of electric shock on Desmodium leaflet—Incapability of tetanus—-Extra pulsation induced by electric shock—Relative effectiveness of electric stimulus at diastolic phase—Effect of transmitted excitation on normal pulsation of heart and on pulsation of Desmodium leaflet-—Effects of acceleration and inhibition : , : : : g : : 318 Effect of lowering of temperature on rhythmic pulsation of cardiac tissue—Similar effect on the pulsation of Desmodium— Increase of systolic limit during cooling—Minimum tempera- ture for arrest of pulsation—Arrest by cooling and subsequent revival by warming—Increase of diastolic limit during warming—Effect of rise of temperature on the pulsation of frog’s heart—Similar effect on the pulsation of Desmoditum— Effect of rise above and return to normal temperature— Diminution of systolic contraction during rise of temperature —lIncrease of systolic contraction during fall of temperature— Permanent arrest due to heat-rigor . : “ ‘ : 323

Application of gaseous or liquid reagents—Modifying influence of tonic condition of specimen, strength, and duration of appli- cation—Effect of sugar solution—Effect of alcohol—Action of carbonic-acid gas—Effects of anesthetics, ether, and chloro- form—Action of carbon disulphide—Effect of copper sul- phate solution—Effect of potassium cyanide solution—Anta- gonistic actions of acids and alkalis on the pulsations of the heart and of Desmodium—Similarities of reaction in rhythmic tissues animal and vegetal . : 5 - : 332

1. Diagrammatic representation of Response Recorder : : 6 2. Response curve of leaf of Mimosa : : - : - i 3. Resonant Recorder, upper part . é : : - : ET. 4. General view of the Resonant Recorder and accessories . Z 20 5. Record showing advantage of intermittent contact : : 21 6. Electro-thermic stimulator . : 3 : : : 25 7. Response of Mimosa to indirect thermal stinelation : ; 20 8. Response to stimulus of constant electric current . : SPST g. Direct stimulation by condenser discharge . : : 28

Io. Record of response to stimulation by condenser discndeat : 30 11. Arrangement for applying single make- or break-shock . 7) 32 12. Records giving apex time of response of Mimosa . - =) «38 17. Erectile response of leaf of Mzmosa, due to local siienitation of 29. Increasing response under increasing stimulation . : a. Oe 32. Photograph of duplex type of Recouciat Fescndacy: : 1) 0G Abolition of motile excitability of pulvinus by absaratien of water . :

59. Abolition of response to warming or cooling after passing thre the death-point . 61. Thermo-mechanical inversion indicating deathcnnint of leat of bean ; 65. Simultaneous record of vibrating recorder and exciting tunica fork : - : 2 : : = 67. Two successive records exhibiting identity of latent period of Mimosa 74. Simultaneous excitation in Sa ge tract under alternating- Constancy of latent period under stimuli above the maximal . Determination of velocity of transmission of excitation in Mimosa