The relative modification of geotropic and phototropic excitabilities by an external agent, is determined by the resulting upset of the photo-geotropic balance.
XLV.—ON THERMO-GEOTROPISM
By
Sir J. C. Bose.
I shall in this chapter investigate the effect of variation of temperature on geotropic response. We have to bear in mind in this connection, that for the exhibition of geotropic curvature two conditions are necessary: (1) the presence of a perceptive organ to undergo excitation under the stimulus of gravity, and (2) the motility of the organ. A motile organ, including both the pulvinated and growing, will exhibit no geotropic effect on account of the depression of the power of perception through seasonal or other changes, or in the entire absence of the perceptive organ. The organ may, on the other hand, possess the geo-perceptive apparatus, but no visible movement can take place in the absence of motility of the tissue.
As regards the modifying influence of temperature on geotropic curvature, the effect will depend on two factors:
(1) the influence of variation of temperature on geo-perception by the sensitive layer, and
(2) the modifying effect of temperature variation on the motile reaction.
