Page:Life Movements in Plants.djvu/191

Rh dots (Fig. 59A). For securing regularity in the rate of

Fig. 59. — Crescographic record? : (A) successive records of g;TOwth at inter- vals of one second (magaifacation 10,000 times), (a) Effect of temperature on a stationary plate; N, normal rate of growth; C, retarded rate under cold; H, enhanced rate under warmth: (6) record on moving plate, where diminished slope of curve denotes retarded rate under cold. (Magnification 2,000 times.)

growth, it is advisable that the plant should be kept in uni- form darkness or in uniformly diffused light. So sensitive is the recorder that it shows a change of growth-rate due to the slight increase of illumination by the opening of an additional window. One-sided light, moreover, gives rise to disturbing phototropic curvature. "With the precautions described the growth-rate in vigorous specimens is I'ound to be very uniform.

After the completion of the first vertical series, the recording plate was moved 1 cm. to the left ; the tip of the recorder was brought once more to the top by the micrometer screw, S, (Fig. 58), and the record taken once more after an interval of 15 minutes. The magnified growth for 4 seconds is 3<S mm. in the first record ; it is precisely the same in the record taken fifteen minutes after. The successive growth elongations at intervals of 1 second is practically the same throughout, being 9*5 mm. This uniformity in the spacings demonstrates not only the