434 LIFE MOVEMENTS IN PLANTS 



down-movement, and the geotropic up-movement was com- 

 menced within a few seconds Hfter placing the petiole in 

 a horizontal position (Fig. 160). The successive dots in 

 the record are at intervals of 20 seconds and the second 

 dot already exhibited an up-movement ; the latent period 

 is therefore shorter than 20 seconds. It will thus be seen 

 that the latent period in this case is of the same order as 

 the hypothetical period of migration of the statoliths. 



I may state here that I have been successful in 

 devising an electric method for the determination of the 

 latent period, in which the disturbing effect of the weight 

 of the organ is completely eliminated. Applying this 

 perfect method, I found that the latent period was in 

 some cases as short as a second. The experiment will 

 be found fully described in a later chapter. 



THE COMPLETE GEOTEOPIC CURVE. 



The characteristics of the geotropic curve are similar 

 to those of other tropic curves. That is to say the 

 susceptibility for excitation is at first feeble ; it then 

 increases at a rapid rate ; in the third stage the rate 

 becomes uniform ; and finally the curvature attains a 

 maximum value and the organ attains a state of geotro- 

 pic equilibrium (cf. page 353). The period of comple- 

 tion of the curve varies in diff:erent specimens from a 

 few to many hours. 



Experiment 166. — The following record was obtained 

 with a bud of Cri?iu?n, the successive dots being at 

 intervals of 10 minutes. After overcoming the efiEect of 

 weight (which took an hour), the curve rose at first 

 slowly, then rapidly. The period of uniformity of move- 

 ment is seen to be attained after three hours and 



