The induced electric variation on the upper and on the lower side indicates that the layers of tissue contiguous to the upper perceptive layer undergoes contraction, while those contiguous to the lower perceptive layer undergoes expansion.
[38] Haberlandt—Ibid, p. 597.
XLIV.—ON GEOTROPIC TORSION
By
Sir J. C. Bose,
Assisted by
Guruprasanna Das.
I have explained that in a dorsiventral organ, lateral application of various stimuli induces a responsive torsion by which the less excitable side is made to face the stimulus (p. 403). I shall in this chapter show that the effect of stimulus of gravity is in every respect similar to other forms of stimulation.
Fig. 179.—Diagram of arrangement for torsional response under geotropic stimulus. The less excitable upper half of pulvinus is, in the above figure, to the left and the torsional response is clockwise.
The direction of force of gravity is fixed, and we have to arrange matters in such a way that the geotropic stimulus should act on the dorsiventral organ in a lateral direction. In the following experiments the pulvinus of Mimosa is taken as the typical dorsiventral organ. For lateral stimulation, the plant is placed on its side, so that the vertical lines of gravity impinge on one of the two flanks of the organ. In regard to this, I shall distinguish two different positions, a and b. In the a-position, the apex of the stem and the upper half of the pulvinus are to the left of the observer, and in b-position, the apex of the stem and the less excitable upper half of the pulvinus are to the right. The arrangement for obtaining record of the torsional response under a-position is shown in figure 179.