Page:Life Movements in Plants.djvu/193

Rh record is at first taken under normal condition, the subse- quent series being obtained under the given changed condition ; the increase or diminution of intervals between successive dots, in the two series, at once demonstrates the stimulating or depressing nature of the changed condition.

In the second method, the record is taken on a plate moving at an uniform rate by clockwork. A curve is thus obtained, the ordinate representing growth elongation and the abscissa the time. The increment of length divided l)y the increment of time gives the absolute rate of growth at any part of the curve. As long as the growth is uniform, so long the slope of the curve remains con- stant. If a stimulating agency enhances the rate of growth, there is an immediate upward flexure in the curve ; a depressing agent, on the other hand, lessens the slope ot the curve.

I shall now give a few typical examples of the employment of the Crescograph for investigations on growth: the first example I shall take is the demonstra- tion of the influence of variation of temperature.

Stationary method : Experiment 52. — The records, given in Fig. 59 a, were taken on a stj,tionary plate. The specimen was S. Kysoor ; the Crescographic magnifica- tion was two thousand times, and the successive dots at intervals of 5 seconds. The mi'ldle series, N, was at the temperature of the room. The next, C, was obtained with the temperature lowered by a few degrees. Finally H was taken when the plant-chamber was warmed. It will be seen how under cooling the spaces between successive dots have become shortened, showing the diminished rate of growth. Warming, on the other hand, caused a widen- ing of intervals between successive dots, thus demonstrating an enhancement of the rate of growth.