Jagadish Chandra Bose

“ I soon found that a sudden change in the intensity of light induces a marked variation of motile excitability in Mimosa. Thus on bringing a highly sensitive plant to a dark room its excitability is found to disappear. This abolition of excitability is generally speaking temporary, since the plant often regains its sensitiveness after about an hour, though still kept in the dark. The fact that under normal conditions it is the sudden diminuntion of light rather than darkness that induces depression of excitability, is borne out by the fact that the plant is fully sensitive at night. ”

“ The most prominent motile organ in Mimosa consists of a mass of tissue known as the pulvinus, at the joint or articulation of the primary leaf-stalk. The swollen mass on the lower side of this organ is very conspicuous. Under excitation the parenchyma, in this more effective lower half, undergoes 'contraction,' in consequence of which there is a fall of the leaf. This sudden movement constitutes the mechanical response of the leaf to the impinging stimulus, just as the contractile movement of a muscle in similar circumstances forms its characteristic mechanical response. ”

“ For precision in such a determination it is necessary to discover a temperature which is of itself efficient to initiate an abrupt death-change. On the other hand, there must be a certain latent period after the expiration of which the change would be outwardly manifested. An interval will elapse, moreover, during which the tissue is attaining the temperature of the bath. If the rate of rise of temperature be too rapid, then, owing to the lag caused by the two factors, by the time the death-spasm commences the recorded temperature may have gone beyond the actual death-point. ”

“ The record will not now labour under the defects inseparable from the friction of continuous contact. Instead of this, we shall have the vibrating writer tapping a record which is practically free from friction. For it will be understood that, as in our concrete example, a recording-point which is vibrating ten times each second will execute one entire to-and-fro movement in one-tenth of a second. The duration of contact, at the extreme forward end of the swing, will represent only a small fraction, say one-fifth, of the entire period of one vibration. ”

“ A stronger stimulus, generally speaking, requires a longer period for recovery. The influence of season is also a factor to be taken into consideration. Under the physiological depression induced by winter, the responsive process is appropriately modified. The excitability of the tissue becomes depressed. An intensity of stimulus which in summer was effective, becomes in winter ineffective. To evoke response much stronger stimulus has to be employed. The latent period is prolonged and the amplitude of response reduced. ”

“ In a very excitable condition we may suppose the slightest shock of stimulus would evoke a very large responsive expression; in a state of depression, on the other hand, the strongest stimulus would induce only a feeble reply. The relation between the stimulus and the response would thus form a gauge of the physiological condition of the organism. The invisible fluctuating changes taking place in the plant, under the changing conditions of the environment, might in this way be made to reveal themselves. ”

“ There are many important problems which wait for their solution till some such means of inquiry is found. What, for instance, are the various forms of stimulus which evoke an answering reaction in the plant? Again, has a given plant-tissue, like animal muscle, any definite perception-period capable of exact measurement? Is the responding tissue susceptible of fatigue? Is the intensity of its answer dependent on the intensity of the blow? Is the excitation that may be caused at one point transmissible to a distance, as along animal nerve? ”

“ The stimulus of unvarying intensity must also be made to act automatically upon the specimen. Under these conditions any variation that may be observed in the record will be due to changes of excitability induced as an after-effect of the stimulus itself.
Maintaining the stimulus-intensity absolutely constant is not so easy to secure with a single make- or break-shock, since the intensity of such a shock is liable to variation, according to the degree of suddenness with which it is effected; but the total additive value of a group of such shocks may be expected to be fairly constant. ”

“ When the motile pulvinus of Mimosa is subjected to an exciting shock, a short time elapses between the incidence of this shock and the initiation of the responsive movement. This short interval is known as the Latent Period. In a responding muscle, similarly, contraction does not occur instantaneously on the application of stimulus. The latent period in this case is determined from the record of the muscle-twitch. When after the application of stimulus the muscle has not yet begun to contract, the record appears as a straight line. ”

“ In all these cases excitation may be either direct or indirect. In the case of muscle, with its attached nerve, we may cause excitation directly by applying the various forms of stimulus on the muscle itself, or indirectly by applying them on the nerve. In the latter case excitation is transmitted by the conducting-tract—the nerve—and reaching the muscle after a brief and definite interval, induces there the usual contraction.
Taking the case of Mimosa, we may similarly have either direct or indirect excitation. Excitation is direct when it is applied, say, on the contractile pulvinus itself. ”

“ This particular intensity, the feeblest that is effective, we designate the minimal stimulus. As We now proceed to increase the stimulation by pushing the secondary nearer to the primary, we find the amplitude of the response is progressively enhanced, and ultimately we reach an intensity beyond which there is no further increment of amplitude. This intensity we designate the maximal stimulus. When the plant is in an exceedingly vigorous condition, the minimal intensity is low and the range between maximal and minimal is narrow. ”

“ If the plant is subjected to a gradual rise of temperature, there would arrive a time when the death-change will begin to occur. In the animal an early symptom of death is the setting in of rigor mortis. We shall find that in plants also a death-spasm, analogous to the death-throe of the animal, occurs at a critical moment. ”

“ Storm and sunshine, the warmth of summer and the frost of winter, drought and rain, all these and many more come and go about it. What coercion do they exercise upon it? What subtle impress do they leave behind? ”

“ As the steel wire has to be made extremely fine, in order to reduce to a minimum the inertia of the recorder, the resulting pull exerted on it is very slight, unless an excessively strong current be sent round the electro-magnet. Again, unless the intermittent closures of the electric circuit be properly timed, the writing-index may be subjected to attraction in the course of its journey, now to the recording-surface and again away from it. In the latter of these cases its vibration, on which the intermittent contact depends, is totally destroyed. ”

“ The exaltation of excitability induced by stimulating agents is exhibited by the enhancement of amplitude of response. The effect of depressing agents is seen in the diminution of amplitude of response; in this class may be included agents which have slight narcotic action. In all these cases the removal of the gas is attended by the restoration of normal excitability of the plant. A curious fact noticeable in this connection is the phenomenon of accommodation. Under the action of a slightly depressing agent, there is induced a diminution of excitability. ”

“ Mechanical response of Mimosa is due to differential contraction of the upper and lower halves of pulvinus.
Erectile responses of Mimosa may be obtained by local stimulation of the upper half of pulvinus.
Distinction of plants into sensitive and ordinary is arbitrary. Under suitable conditions, ordinary plants, so-called, may be made to exhibit motile response.
By means of electric response it may be shown that every plant, and every organ of the plant, is sensitive and responds to stimulation by a definite electric change. ”

“ As the death-spasm is a form of physiological response we should expect the curve of death to undergo modification under physiological variation. One such modification would lie in the translocation of the point of inversion, or the displacement of the death-point. Thus age has some influence, the death-point of very young specimens being lower than that of mature ones. ”

“ A light six-rayed wheel is attached to the axis of the seconds-hand, and during the course of a single complete revolution, that is to say, in a minute, the projecting rays press the spring-key six times at intervals of 10 seconds each (fig. 13) . It is only during the short interval when the key is pressed that the circuit is completed and the recorder set in vibration to make its dots. Each dot made, it should be remembered, is the result of a succession of strokes inscribed by the vibrating recorder 10 times in the second. ”

“ In strong contrast to the energetic animal, with its various reflex movements and pulsating organs, stands the plant in its apparent placidity and immobility. Yet that same environment, which with its changing influences so strikingly affects the animal, is playing upon it also. ”

“ Having shared the prevailing belief that the sensitiveness of the plant was very feeble compared with that of the animal, I was considerably surprised to find that the intensity of induction-shock which is barely sufficient to induce sensation in man is quite enough to cause excitatory fall in a Mimosa of moderate sensitiveness. ”

“ A general flattening, along the whole length, tends to maintain the vibration in a definite plane, otherwise the free tip is apt to execute an elliptical vibration. The tuning of the vibrator with the coercer is not very difficult when the vibration-frequency is low, say 10 per second. But when the frequency is high, say 100 or 200 times in a second, an exact tuning is essential. The slightest variation of the length of the coercer will either bring about full resonance or make it entirely ineffective. When the tuning is nearly but not quite perfect, then we have the phenomenon of beats. ”

“ We may subject the tissue to shock of either make or break at will by employing an additional short-circuiting key. When this key is down, the shock from the secondary coil is practically diverted across the better conducting-path provided by the key, so that for practical purposes none passes through the plant tissue. If it is desired to cause successive excitations by make-shock only, then the short-circuit key is raised when the primary circuit is made, and pressed down when this is broken. ”

“ The absorption of energy from without, by Whatever form of stimulation, will improve the tonic condition of the plant, with consequent enhancement of excitability.
Taking a plant in a subtonic condition, then, we may expect that any application of stimulus will increase its excitability, a fact which will find expression in a growing amplitude of response. This enhancement of excitability will reach a limit at which the plant will be in an optimum condition. After reaching this climax there may be a reversal, with decline of excitability, a state of things which we associate with fatigue. ”

“ The break-shock is more effective in inducing excitation than the make-shock.
Stimulus, singly ineffective, becomes effective on repetition. The effective stimulation is equal to the individual intensity of stimulus multiplied by the number of repetitions.
The effect of load on the response of Mimosa is similar to that on the contractile response of muscle. With increasing load the height of response undergoes a progressive diminution With shortening of period of recovery.
Within limits, the amount of work performed by a muscle increases with the load. ”

“ The occurrence of death-spasm may also be shown by means of ordinary plants. If we take a hollow tubular organ, such as the hollow leaf-stalk of gourd or hollow flower-stalk of any other plant, cut it in the form of a spiral and subject it to the rising temperature of the bath, there is noticed at first an expansive movement of uncurling of spiral. ”

“ If We know the natural frequency of vibration of the recording-index, and if by means of some mechanism we can send periodic currents of exactly the same frequency through the electro-magnet, then the intermittent magnetic pulls will exactly synchronise with the natural swings of the writing-index. ”

“ Although we thus have various forms of stimulus at our disposal for inducing individual and isolated responsive contractions in Mimosa, yet we are confronted with very great difficulties when we wish to obtain a series of uniform excitations for quantitative investigation. It is obvious that chemical forms of stimulus would be impossible for successive excitations. The objection to a mechanical blow, as the stimulus to be employed, lies in its liability to cause a mechanical jar and thus to disturb the record. ”

“ On the fall of the leaf, under excitation, it would pull down with it the attached arm of the lever. The vertical writer would then also move, say, to the left. If the finely pointed bent end of the writer were to press lightly against the smoked surface of a glass plate, which was allowed to fall, at a uniform rate, by means of clockwork, a curve would then be traced which would not only record the responsive movement and recovery but also give their time-relations (fig. 1) . ”

“ The intensity of the current can be maintained uniform if we always employ the same battery, say a 4-volt accumulator or storage-cell. As the break of a current is accomplished more quickly than make, the break-shock, as we have seen, is more intense than the make-shock. ”

“ The motor is fully wound at the beginning, and the partial unwinding during one revolution is exactly compensated before the next observation by the winding necessary to pull up the plate. Owing to the constancy of this winding, the rate of fall in successive experiments is kept the same. The pressure of the handle K, which releases the plate, also causes 'make' of the current in the primary coil. This circuit of the primary coil is completed in addition through a contact-breaking device.
This consists of a long strip of ebonite, fixed along one edge of the recording-plate carrier. ”