Page:Life Movements in Plants.djvu/235

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XVI.—ACTION OF LIGHT ON GROWTH


By


Sir J. C. Bose,


Assisted by


Guruprasanna Das.


The next subject of inquiry is the normal effect of light on growth. I speak of the normal effect because, under certain definite conditions, to be described in a later Paper, the response undergoes a reversal. The Crescograph is so extremely sensitive that it records the effect of even the slightest variation of light. Thus, as I have already mentioned, the opening of the blinds of a moderately-lighted room induces, within a short time, a marked change in the record of the rate of growth. The conditions of the experiment would thus become more precise if the growth-rate in the absence of light is taken as the normal. The specimens are, therefore, kept for several hours in darkness before the experiment. But this should not be carried to the extent of lowering the healthy tone of the plant.

I shall, in the present Paper, determine the characteristic response to light in variation of growth, the latent period of response, the effects of light of increasing intensity and duration, and the effects of the visible and invisible rays of the spectrum.

METHOD OF EXPERIMENT.

The plant was placed in a glass chamber kept in humid condition. The sources of light employed were: (1) an

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