Page:Collected Physical Papers.djvu/411

Rh high magnification, and for the automatic record of the magnified rate of growth.

The High Magnification Crescograph gives automatic record of growth under a magnification of ten thousand times (p. 348). With this it is possible to obtain growth-record in a time shorter than a second and determine its absolute rate, which in S. Kysoor is 0.95 μ per second, where μ represents micron or 0.001 mm.

Effect of variation of temperature.—The effect of rise of temperature in acceleration of growth can be determined in a few minutes (p. 349). It is thus possible to make accurate determinations of the optimum temperature for maximum growth and the minimum temperature for the arrest of activity.

Effect of Chemical agents.—The effect of manures, anæsthetics, drugs and poisons can be similarly determined in a few minutes and with unprecedented accuracy. The effect of a chemical agent is found to be modified by the dose of application (p. 351).

The Balanced Crescograph.—A still higher sensitiveness in recording the slightest change of growth was secured by the method of balance in which by a clockwork device, the plant is made to descend exactly at the same rate at which the growing tip of the plant was rising (p. 352). The rate of growth is thus accurately compensated and the recorder dots a horizontal line of balanced growth. The minutest change induced in the rate of growth by the environment is at once indicated by the upset of the balance shown by the up and down movements of the curve. The method is so extremely sensitive that it detects and records variations in the rate of growth so excessively minute as $1⁄1500$ millionth of an inch per second.