1917] 



WEB— BR YOPII YLLUM 



43 



removed 



In the former case the 



stretching 



force of wood and pith on the side where the cortex is removed is 

 lacking. Such stems show in a striking way the influence of the 

 position of the leaf upon the geo tropic curvature. 



More than a dozen stems whose cortex was removed on 

 upper side were suspended horizontally (fii^s. 26, 27). Each stem 

 had one leaf left, one-half of the stems having the leaf at the base 



the 



(% 



while 



I. Only the 



leaf at the 



able 



d 



any geotropic bending. This shows that 

 the geotropic growth of the cortex must 

 be considerably less when the leaf is at 



when it is at the apex. 



Fig. 25 



When the cortex was above (lie:. 2O and the leaf 







the curvature due to the effect of the removal of the cortex 

 on one side of the stem, which takes place instantly after the 

 operation . 



When the leaf is left at the apical end and the cortex below, as 

 in fig. 27, the curvature occurs again in the region of the second 

 node behind (basally from) the leaf; and in that node on the lower 

 side the first roots develop (fig. 27). These drawings were made 

 9 days after the beginning of the experiment. If all the leaves are 

 removed on such a stem it is no longer able to bend geotropically. 



