Page:Life Movements in Plants Vol 2.djvu/25



WE shall in the succeeding series of papers deal with the subject of tropism in general. Different plant organs undergo curvature or bending, sometimes towards and at other times away from the stimulus which induces it. The problem is very intricate; the possibility of its solu- tion will depend greatly on the accurate determination of the immediate and after-effects of various stimuli on the responding organ. The curvature induced in the growing organ is brought about by variation, often extremely slight, of the rate of growth; the result, moreover, is liable to be modified by the duration and point of application of stimulus. The difficulties connected with the problem ean only be removed by the detection and measurement of the minutest variation in growth, and by securing «a continuous and automatic record of the entire history of the change.

In the chapter on High Magnification Crescograph an account is given of the apparatus which I have devised by which the rate of growth may be inagnitied from ten thousand to ten millions times. It iy thus possible to meagure the imperceptible growth of plants for a period shorter than a single second. The variation of normal rate of growth is also found by measuring successive growth records on a stationary plate at regular intervals, say of ten seconds, or from the flexure in the growth-curve taken on a moving plate (p. 163).

I was next desirous of exalting the sensitiveness to a still higher degree by an independent method, which would