Page:The Modern Review (July-December 1925).pdf/748

720 of the muscle being followed by galvanometer deflection in the opposite direction. A single mechanical pulsation of contraction and expansion is thus attended by a corresponding electric pulsation. If electric connection be next made with the heart of the animal, the heart-beat is independently manifested by the corresponding electric pulsation. For localising the heart of the plant, the Electric Probe was gradually introduced across the stem; when the Probe comes in contact with the active cell, it sends out electric signals which are automatically recorded by the Galvanograph. The up-stroke of the records indicates expansion and absorption of sap, while the down-stroke indicates expulsive contraction. It is thus found, that the cells actively engaged in propulsion of sap, are in a state of incessant pulsation, expanding and contracting by turns. Each cell during its phase of expansion absorbs water from below, and expels it upwards during the phase of contraction. The ascent of sap thus takes place by the coordinated activity of a series of vertically situated cellular pumps.

It was however objected that this proof was indirect; what was wanted was a tangible demonstration of the change of sap-pressure by excitation or depression of the cellular pump, and, if possible, to record the constituent pulse itself.

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Let us follow the course of the sap-stream with clear inner vision. The plant is pumping the sap along the stem; the passage of each pulse

must therefore be attended by an infinitesimal expansion. After the brief passage of the pulse-wave, the stem would revert to its original diameter, till the next pulse re-inflates it once more. A stimulant would make the heart-pump work more energetically, either by making the length of the stroke larger or the frequency quicker. The sap-pressure would then increase, as would be evidenced by the greater inflation of the stem. Under depressors, the change would be of an opposite character. What was seen by the mind’s eye, now requires experimental verification. For this, it is necessary to construct artificial organs of perception of surpassing delicacy and sensitiveness. The Plant-Feeler or the new type of Sphygmograph consists of two rods, one of which is fixed and the other movable, the stem of the plant being placed between they two. The expansive pulse-wave pushes the movable rod outwards by an infinitesimal amount which has to be magnified at least fifty thousand times by the special device shown. This amplification is sufficient to enlarge the wave-length of sodium light to 25 mm. Great precautions have to be taken to eliminate all mechanical disturbances by the invention of special shock-absorbers. The artificial earthquake produced by the passage of motor-vans is however introducing increasing difficulty in the use of supersensitive instruments. Occasional respite for obtaining satisfactory record is obtained when there is a lull in the traffic I have sometimes been compelled to carry the instruments to my Mayapuri Research Station at Darjeeling, situated at a height of 7000 feet. The Laboratory built on a substratum of solid rock affords sufficient protection against all mechanical disturbance.

The apparatus giving a magnification of fifty thousand times is quite effective in giving an immediate record of effects of stimulants on the active cells, a sudden rise of the curve demonstrating the resulting increase of sap-pressure. Depressing agents, on the other hand, produce a fall of the curve showing a diminution of pressure. The sensitiveness of the apparatus is, however,