432 LIFE MOVEMENTS IN PLANTS 



period ofll'ei's a serious difficulty in the acceptance of the 



theory of statoliths. But it may be urged that the 



latent period has hitherto baen obtained by relatively 



crude methods, and I therefore undertook a fresh 

 determination of its value by a sensitive and accurate 



means of record. 



PETERMINATION OF THE LATENT PERIOD. 



As regirds the interpretation of the record of geotropic 

 movement, it should b^ borne in mind that after the 

 parceptioii of stimulus a certain lime must elapse before 

 the induced growth-variatioix will result in curvature. 

 There is again another factor which causes delay in the 

 exhibition of true geotropic movement ; for the up-move- 

 ment of stems, in response to the stimulus of gravity, has 

 to overcome the opposite down movement, caused by 

 weight, before it becomes at all perceptible. On account 

 of the bending due to weight there is a greater tension 

 on the upper side, which as we have seen (p. 193), 

 enhances the rate of growth, and thus tends to make 

 that side convex. The exhibition of geotropic response 

 by induced contraction of the excited upper side thus 

 becomes greatly delayed. In these circumstances I tried 

 to discover specimens in which the geotropic action would 

 be quick, and in which the retarding effect of weight 

 could be considerably reduced. 



Geotropic response of Jioiver stalk of Tuheruse : Experi- 

 ment 164. — For this 1 took a short length of flower 

 stalk of tuberose in a state of active growth ; the flower 

 head itself was cut off in order to remove unnecessary 

 weight. After a suitable period of rest for recovery from 

 the shock of operation, the specimen was placed in a 



