Page:Collected Physical Papers.djvu/369

In the second method, the record is taken on a plate moved at a uniform rate by clockwork. A curve is thus obtained, the ordinate representing growth-elongation and the abscissa, the time. The increment of length divided by the increment of time gives the rate of growth at any part of the curve. As long as growth is uniform, so long the slope of the curve remains constant. Enhancement of the rate of growth by a stimulating agent causes an upward flexure of the curve; a depressing agent, on the other hand; lessens the slope of the curve.

Determination of the Absolute Rate of Growth

The record of growth was taken with a vigorous specimen of S. Kysoor on a stationary plate.

Fig. 110. Crescographic Records.

(A) Successive record of growth at intervals of one second (magnification 10,000 times). (a) Effect of temperature taken on a stationary plate; N, normal rate of growth; C, retarded rate under cold; H, enhanced rate under warmth; (b) record on moving plate, where diminished slope of curve denotes retarded rate under cold. (Magnification 2,000 times.)

For securing uniformity of growth, it is advisable that, the plant be kept in darkness or uniform diffused light.