GEOTROPISM 



433 



horizontal position, and its record taken. The succes- 

 sive (lots in the curve are at intervals of 20 seconds, and 



Fiii. lo'.t. 



Fig. U>(i. 



Fig. Inlt. — Geotropic rei-ponse of flower stalk of tube ro«' : preliminary down- 

 movement is due to weight. 



Fig. 160. — Geotroinc response of petiole of Tiofxpolion : latent period shorter 

 than 20 seconds. 



the geotropic up-movement is seen to be initiated 

 (Fig. ir)9) after the tenth dot, the latent period being 

 thus li minutes and 20 seconds, the greater part of which 

 was spent in overcoming the down-movement caused by 

 the weight of the organ. 



Geotropic response of petiole of Tropaeolum : Experi- 

 ment 165. — I expected to obtain still shorter latent 

 period by choosing thinner specimens with less weight. I 

 therefore took a cut specimen of the petiole of Tropceo- 

 lum^ and held it at one end. The lamina was also cut 

 off in order to reduce the considerable leverage exerted 

 by it. The response did not now exhibit any preliminary 



