XLIX.—DAILY MOVEMENT IN PLANTS DUE TO
THERMO-GEOTROPISM
By
Sir J. C. Bose,
Assisted by
Lalit Mohan Mukherji.
Of the vast number of daily movements perhaps the largest proportion is due to thermo-geotropic reaction and its modifications. Thermo-geotropic movements have the following characteristics:
1. The organs are sensitive to the stimulus of gravity and the periodic movements are brought about by variation of geotropic curvature under change of temperature.
2. The movement is not confined to growing organs, but is also exhibited by organs which are fully grown and even by rigid trees.
3. The periodic movement is closely related to the diurnal variation of temperature. Fall of temperature from thermal-noon (about 2 p.m.) to thermal-dawn (about 6 a.m.) is attended by a movement of erection; rise of temperature from thermal-dawn to thermal-noon is followed, on the other hand, by a reverse movement of fall.
That the movement is primarily due to variation of temperature will be demonstrated in two different ways:
(a) by the change of normal rhythm of movement by artificial transpositions of periods of maximum and minimum temperature, and
(b) by the abolition of periodic movement through maintenance of constant temperature.