Plant Autographs and Their Revelations

The other tree from which sugary sap is collected is the Palmyra Palm (Borassiis flabellifer) ; it is a tree of very slow growth and lives for more than a century. The sap is drawn from the cut end of the flowering spike or spadix, which appears only in early summer. Fermentation soon becomes pronounced at high temperatures, and very special precautions have to be taken to obtain the sap unfermented. Ordinary cleaning of the collecting pot is found insufficient for the purpose ; the prevailing custom is to smear the vessel with quick-lime and wash it afterwards. This antiseptic treatment is usually successful in securing the fresh sap as a drink.

The total quantity of sap given out by a single tree during its life may be as much as 120,000 litres. The sap is rich in sugar, the content being as high as 10 per cent. It may be regarded as a very efficient plant for the manu¬ facture of sugar, since the total yield from a single tree during its lifetime may reach the enormous total of 12,000 kilograms or nearly 12 tons. a very interesting variation. For the investigation of this, I devised the Tilter, by which definite quantities of sap collected are automatically recorded for hours and days.

The rate at which the sugar-containing sap is given out is not the same at all hours of the day and night, but shows The recording apparatus may be placed inside the laboratory at any distance from the tree. As soon as the collecting cup of the Tiber becomes full, it overturns and empties itself. This upset completes an electric circuit each time, and the electric signal thus sent makes a mark on a recording drum. All that is necessary is to count the number of marks, which are closer together when the exudation is copious, and wider apart when the yield is scanty. The automatic records show that the rate of the yield of sap is at its minimum at about i p.m. and at its maximum at about 2 A.M. (fig. 85). The exudation at night is thus seen to be very much greater than in the day-time.

Note the separation of the dots after i p.m. and their closeness Careful measurement of the yield of a particular Date Palm showed that it gave 700 cubic centimetres of sap between six in the morning and six in the evening, while for the succeeding twelve hours of night the exudation was 2150 cubic centimetres, an amount three times as great. The explanation of this difference is to be found in the fact that the tree loses water by transpiration from the leaves as well as by the exudation of sap from the wounded surface. Consequently maximum transpiration should correspond with minimum exudation, and z’icc versa. As the loss by

transpiration is feeble at night, the exudation of sap from the cut surface is relatively greater. During the day-time, on the other hand, the loss due to transpiration from leaves is very great; hence the smaller yield of sap. I now turn to the explanation of the exudation of sap by the Indian Date Palm. Many trees before the unfolding of leaves in early spring are filled with sap under considerable pressure, on account of which the sap exudes as soon as a hole is drilled into the tree. But in the Palm no sap exudes from a hole drilled in the trunk. I felled a tree, and the cut ends of the trunk did not exude a single drop of sap. Por¬ tions of the tissue taken from the interior of the trunk were found to be almost dry, and it was only after considerable compression that a small quantity of sap could be squeezed out. This experiment proves that there is no root-pressure to cause exudation from an injured surface. It should be remembered, in this connection, that the Date Palm grows in a dry or even arid soil ; hence necessity compels the tree to exploit fully the scanty and precarious supply of water. The tree sends out more than a thousand roots to a con¬ siderable distance, each as thick as one’s little finger. I followed each of these roots to a distance of more than twenty feet, yet the end was not in sight. The trunk of the tree is thus slowly charged with water absorbed by the enormously extended root-system, the sap being held in the trunk of the tree with great tenacity.

A hole made in the trunk, as stated before, does not yield a single drop of sap from the Palm. How, then, is the tree induced to give out its hoarded treasure? The normal inactivity of the wounded surface of the Palm is shown by the fact that there is no exudation at first even when vertical slices are cut in the upper part of the stem. The sap begins to exude only after repeated slicing of the stem for nearly a week. What is the explanation of these facts ? It has already been shown in a previous chapter that a living tissue may be roused from a state of inactivity to multiple activity

by adequate stimulation. A very inactive tissue would naturally require a very strong stimulus or a succession of stimuli which became effective by their cumulative effects. In order to induce exudation from the Palm, the intense wound-stimulus had, therefore, to be repeated for several days in succession. In the Palmyra Palm, in which the spike of flowers or spadix yields the sap, the process of coercion is somewhat different. There is no exudation when the tip of the spadix is cut off ; exudation takes place only after the inflorescence has been subjected to a special treatment for several days. For this purpose two different processes have been elaborated in different countries, which may aptly be described as ‘butting’ and ‘milking,’ from the not very far¬ fetched analogy of the action of the calf to make the cow yield her milk.

The Malaya people strike the spike of the flower with a wooden mallet repeatedly for nearly a fortnight, after which the sugary juice is yielded from an incision. In India the method employed is perhaps more humane. The long spadix is held tightly between the fingers and kneaded from above downwards, the process being similar to the milking of a cow. This milking process is repeated day after day for a week. Cutting of the tip is then followed by a copious yield of sap. The preliminary hammering may be compared to the ‘butting’ of the calf, the ‘kneading’ to the usual process of milking.

The methods employed to induce the yield of sap by the previously inactive tissue of the Palm are fundamentally similar. They have one object in common — namely, the arousing of the dormant activity by the repeated application of stimulus, which may take the form of repeated cuts, repeated blows, or repeated kneading. As a result of this treatment the inactive tissue becomes as active as a glandular tissue, and is thus able to maintain the exudation even though there be no internal sap-pressure to urge it.

The electric method enabled me, as explained in a previous chapter, to prove that a propulsive tissue runs throughout the length of the plant, and that the flow of sap is brought about by a mechanism essentially similar to that of the circulation of the blood in the animal. The rhythmic pul¬ sation of this tissue in the plant has, as already explained, been observed only by means of the corresponding electric pulsations. The channel for the transport of sap may be regarded as an artery, the throbbing activity of which is its pulse-beat. Is it at all possible to record the actual pulse-beat mechani¬ cally? If we can succeed in doing this, the pulsatory activity of the plant will have been demonstrated by two entirely independent methods, the electrical and the mechanical.

There are yet other rigorous tests which may serve to demonstrate the essential similarity of the mechanisms for the circulation of the sap and of the blood. Various alkaloids induce characteristic reactions in the pulse-beat of the animal; do they similarly affect the pulse-beat of the plant? The pulsations of the animal heart may be recorded directly by the Cardiograph, or indirectly by the Sphygmograph. The Cardiograph is essentially a magnifying lever, the short arm of which is attached to the beating heart, the longer arm recording the beats on a moving plate of smoked glass. Under a stimulating drug the pumping activity is greatly enhanced, the record showing an increased frequency or

increased amplitude of pulsation. A depressing agent, on the other hand, brings about a diminution in the frequency or amplitude of the heart-beat. The heart-beat has a corresponding pulse-beat in the arteries. The enhanced or depressed activity of the heart and the consequent changes of blood-pressure can be made out from the records given by the arterial pulse. In the human subject the radial artery is on the surface, at the wrist. The pressure-variation in the artery can be recorded by the Sphygmograph, which consists of a series of magnify¬ ing levers actuated by the? impulse. This would obviously be impossible were the artery buried under other indifferent tissues instead of being on the surface.

It has been shown that the sap is propelled by the rhythmic pulsation of the propulsive layer in the stem. But any attempt to feel the pulse of the plant would, by the very nature of the case, appear to be hopeless, for the amount of expansion and contraction at each pulse would be beyond even the highest powers of the microscope to detect, since the amplitude would be something like a millionth of an inch. The active cells, moreover, are buried in the interior of the plant; how can the invisible and intangible be made accessible ?

Let us follow the course of the sap-stream. As the plant is pumping the sap along the stem, the passage of each pulse must be attended by an infinitesimal expansion. After the brief passage of the pulse-wave, the stem will revert to its original diameter, until the next pulse reinflates it once more. The difficulty of recording the variation of the sap- pressure in the stem arises from the fact that the conduct¬ ing channel, unlike the radial artery, is buried under other tissues; the area of the channel is, moreover, insignificant compared with the total section of the stem. The infinitesi¬ mal dilatation and contraction due to the pulse-wave can only be detected by a Plant-Feeler of surpassing delicacy and sensitiveness.

A supersensitive apparatus for the purpose has been realised in the Optical Sphymograph, in which a compound magnification is produced by a lever and a rotating mirror. The stem is placed between two rods, one of which is fixed and the other movable. Two v-shaped pieces of ivory carried by the two rods touch two diametrically opposite points of the stem at R and C. The fulcrum-rod F of the movable lever is supported on jewel bearings. This lever is made of a porcupine quill, which combines lightness and

rigidity in an unusual degree ; its inertia being negligible, it quickly follows the movement of the pulse-beat. The lateral pressure of the lever on the stem is adjusted by the spring S, which may be placed either behind or in front of the lever. The length of the lever produces a magnification of about thirty times (fig. 86), which, however, is too slight to render the pulsations visible. It is therefore necessary to superpose a further optical magnification. A thin silk thread tied to the tip of the sphygmograph-lever makes one turn round a thin vertical rod supported both above and below by jewel bearings. The other end of the string is

attached to a fine spiral spring, by which the pressure of contact on the stem can be easily adjusted. The outward movement of the lever L caused by the pulse- wave during expansion rotates the vertical rod in a clockwise direction, contraction producing anti-clockwise rotation. The rotation thus produced is highly magnified by a small mirror M, by which a beam of light is reflected on to a distant screen (fig. 87). Fig. 87. Diagram of the Sph3-gmograph with optical attachment.

is about a million times, which is suflicient for public demonstration of the characteristic effects of different alkaloids on the propulsive tissue of the plant. The complete apparatus is shown in fig. 88. The special applicator carries three small cups, containing respectively a stimu¬ lating, a depressing, and a poisonous solution. One or other of these may be rapidly applied to the cut end of the stem. For the record of the individual pulse-beat of the plant a still higher magnification — namely, of ten million times —

is necessary. This has been rendered practicable by my Magnetic Sphymograph. record in the sphymo- gram. This state of balance is not static but dynamic, consisting of oscillations about a po¬ sition of equilibrium. The alternate expansion and contraction due to rhythmic activity are exhibited in the pulse- records, the dilatation by an up-curve and the contraction by a down- Fig. 89. Record of Cellular Pulsations. curve, these twO being equal (fig. 89). As these pulsations are very minute, as already stated, it requires the very high magnification of ten million times for their

demonstration. They are, however, conspicuously exhibited when the pressure is undergoing any change. The blood-pressure in the animal, as previously explained, can be increased by a stimulant and lowered by a depressant. In the parallel experiment with the plant, the unique opportunity is presented of actually observing the action of the cellular pump, and the unecjual strokes delivered by it during enhancement or depression of the rate of ascent, which cause changes in the sap-pressure. Results will presently be described which establish the important generalisation that a stimulating agent which enhances the rate of ascent gives rise to pulsations the up-stroke of zohich is larger than the down-stroke. A depressing agent produces, on the other hand, a change in the constituent pulsations, such that the down-stroke is larger than the upstroke. Therefore, the stimulative or inhibitor v nature of an agent can at once be discovered bv its effect on the pulse-record. The sensitiveness of this method of observation is extraordinarily great. Taking, for example, the action of a stimulative agent, the immediate eff'ect is a moderately large up-stroke followed by a feeble down-stroke ; the eff'ect increases rapidly until the amplitude of the up-stroke becomes so large as to carry the record off the plate. The frequency of the pulsations is also increased, so that the individual pulsations merge one into the other. The application of a depressant now produces the reverse change. It is interesting at this crisis to note the change in character of the individual pulsations, by which the hitherto increasing pressure is converted into diminishing pressure. After a period of hesitation, the down-stroke becomes predominant; a series of such constituent pulsa¬ tions produce the descending curve which indicates the induced diminution of pressure.

beat of the animal. For the sake of convenience, they may be divided into three classes : ( i ) stimulants, which produce in general an enhancement of activity; (2) (fepressants, causing an inhibition of activity; (3) stimulant- depressants, producing stimulation in minute dose and depression in moderately large dose. For the detection of changes of activity induced in the animal heart, the Cardiograph is more direct and sensitive than the Sphygmograph. But the only apparatus which records the pulse-beat of the plant is the Magnetic Sphygmo¬ graph. The similarity of effects of certain alkaloids on animal and plant will be demonstrated as follows ;

The result in both animal and plant is modified ( i ) by the tonic condition of the tissue and (2) by the dose and duration of application. I shall presently describe certain simple and typical examples. The cardiogram was obtained with the heart of a fish, Ophiocephalus, in which the normal beat remains uniform for a great length of time. The sphygmogram of the plant was obtained with Cosmos, Centaurea and Antirrhinum. Dilute solution of camphor enhances the activity of the animal heart. The stimulative effect is more easily shown with a specimen which is in a somewhat depressed condition. It is obvious that little further enhancement can be induced in a heart that is already in a condition

of maximum activity. The normal record of pulsation of the animal heart is shown in the upper record of fig. 90. Injection of camphor, two parts in a thousand, Fig. 90. Effect of Camphor. Upper record shows normal rate of heart-beat. Rapidly descending line represents expulsion of blood by systolic contraction ; ascending line represents active diastole; horizontal or slightly ascending line, passive diastole and pre-systole, the duration of which is greatly modified by action of drugs. Lower record represents stimulating action of Camphor in quickening the heart-beat. (Heart of Fish.)

Fig. 91. Effect of Camphor on the plant; enhancement of sap- pressure due to increased pumping activity. Note up-stroke of each pulse larger than down-stroke. considerably quickened the heart-beat, as seen in the lower record. The effect of camphor on the plant is shown in fig. 91. The original amplitude of pulsation was feeble, so the record Fig. 92. Action of Morphine : depression of cardiac activity in the fish. Fig. 94. First series gives record of normal cardiac activity ; the second shows depres¬ sion under KBr ; and the third, enhanced activity under musk. (Fish.)

appears as a horizontal line. Application of dilute camphor produced a sudden increase of pressure shown by the ascend¬ ing curve, in which the constituent pulsations show the up-stroke to be larger than the down-stroke. I obtained Fig. 95. Effect of KBr in depressing and of musk in enhancing sap-pressure. similar results with other stimulants, such as musk, pro¬ vided the dose is not excessive. left record in fig. 92 shows the normal heart-beat of the fish; the record to the right shows the effect induced by morphine, the amplitude and the frequency of pulsation exhibiting a depression.

The depressing action of morphine on the pulse-beat of the plant is seen in the next record, the constituent pulsations of the descending curve exhibiting down-strokes of each pulse larger than the up-stroke (fig. 93). Alcohol, even in small doses, produces a depression of the beat. I will next describe the remarkable records obtained by alternate application of a depressant and a stimulant to both animal and plant. For a mild depressant, I used a solution of bromide of potassium. In the first of the series of records in fig. 94 is shown the normal heart¬ beat. After application of bromide of potassium solution, five parts in a thousand, great depression occurred, both in amplitude and in frequency. A solution of musk, one part in a thousand, was next applied ; it not only neutralised the depressing action of the bromide; but enhanced the activity above the normal. In the parallel case of the plant, the bromide was seen to produce great depression; subsequent application of musk not merely removed the depression, but caused a great enhancement of pumping activity and resulting increase of pressure (fig. 95).

Such antagonistic reactions are even more strikingly exhibited under the action of a poison and its antidote. Thus while under the continued action of morphine the plant was on the point of death, as shown by movement of the light-index to the extreme left, application of atropine revived the pulsation; the beam of light moved to the right, indicating the revived life of the plant. A dose of strychnine, one part in a thousand, caused a marked enhancement of the cardiac activity, as seen in the quickened rate of pulsation ; a 2 per cent, solution pro-

duced, on the other hand, a great depression and ultimate arrest of the heart-beat (fig. 96). Parallel effects of stimulation and depression were pro¬ duced in the plant by minute and large doses of strychnine. A dose of a solution of one part in a thousand acted Fig. 96. Action of Strychnine. Increased frequency of cardiac pulsa¬ tions under o.i per cent, solution (upper record). Depression and arrest under 2 per cent, solution (lower record). as a stimulant, increased the sap-pressure: but one of a i per cent, solution caused marked depression and diminution

Cobra-venom acts on the animal as a very deadly poison. When injected subcutaneously it proves fatal when the quantity is as small as 0.00002 gram. There is a popular belief in India that even when a person bitten by the snake exhibits all the signs of death, such as stoppage of respira¬ tion and of pulse-beat, yet there may be a chance of revival. The dead body is, therefore, not cremated as in other cases of death, but placed on a raft and allowed to float down the river.

I investigated the effect of cobra-venom on both animal and plant, and employed for my ex¬ periments desiccated venom, which keeps its deadly property unchanged for many years. After taking the normal rec¬ ord of the vigorously pulsating heart of the flsh, 0.5 c.c. of solu¬ tion of venom, one part in a thousand, was injected into the vein. The amplitude of the pul¬ sation exhibited a rapid decline and the heart-beat came to a complete stop in the course of twelve minutes. Shortly before this, a muscular spasm occurred in the body of the flsh, shown as a down-twitch in the record (fig. 98). _