Life Movements in Plants, Volume II

by Jagadis Chandra Bose

Fig. 200.—Diurnal record of inclined palm tree, of geotropically curved procumbent stem of Tropæolum and the dia-geotropic leaf of palm. Note general similarity between diurnal curve of plants and the thermographic record.

I have also shown that the diurnal movement is determined by the modifying influence of temperature on geotropic curvature. Rise of temperature opposes or neutralises the geotropic curvature; fall of temperature, on the other hand, accentuates it. The particular diurnal movement was not confined to the palm trees, but was exhibited by all plant-organs subjected to the stimulus of gravity.

Fig. 201.—-Diurnal records of leaves of Dahlia, Papaya and Croton.

DIURNAL MOVEMENT OF PROCUMBENT STEMS AND OF LEAVES.

Experiment 210.—In order to demonstrate the continuity of the phenomenon of diurnal movement I took various stems growing in water or land for my experiment. The plants were laid horizontally, till the stems bent up and assumed the stable position of geotropic equilibrium. In figure 200 is given records of the inclined palm tree, of procumbent stem of Tropæolum, and the leaf of the palm tree. The very close relation between the temperature-variation and the movement of different plant-organs is sufficiently obvious.

I shall next give a series of diurnal records of leaves of different plants such as those of Dahlia, Papaya and Croton (Fig. 201). In these also fall of temperature induces an up-movement while rise of temperature causes a fall of the leaf. I shall presently refer to the 'personal equation' by which the record of one plant is distinguished from another.

CONTINUOUS DIURNAL RECORD FOR SUCCESSIVE THERMAL NOONS.

Experiment 211.—The diurnal record given above, was taken from ordinary noon at 12 o'clock to noon next day. The diurnal curve becomes much simplified if the record be taken from thermal-noon (at about 2 p.m.) to the thermal noon next day. The plant-organ becomes erected during falling temperature from thermal-noon to thermal-dawn next morning, and undergoes a fall during rise of temperature from thermal-dawn to thermal-noon. The subsequent diurnal records will therefore be given for 24 hours commencing with 2 p.m. In figure 202 is given diurnal records of geotropically curved stem of Tropæolum and the leaf of Dahlia for two days in succession.