192 



STUDIES IN GENERAL PHYSIOLOGY 



these animals are compelled to assume a definite orientation 

 toward the center of the earth. 1 If the growing stem of an 

 Antennularian is put into any other than a vertical position. 

 3 the growing tips bend until the stem again 



stands vertically, after which it grows straight 

 upward. The root, upon the other hand, grows 

 vertically downward, but not so directly as the 

 stem. The stem is negatively, the root posi- 

 tively, geotropic. The stem ab (Fig. 38) origin- 

 ally stood vertically. I tilted it so that it 

 formed an angle cba with the vertical; the newly 

 formed piece be grew vertically upward after 

 this change in position. I then put the stem 

 back into its old position, after which growth 

 continued in a vertical direction cd. Fig. 39 

 also shows an upward bending of the stem. 

 Roots growing downward are shown in W (Figs. 

 40 and 41). While the tip of the growing 

 stem does not weary of growing vertically 

 upward whenever its position toward the 

 horizon is slightly altered, the root is 

 much more sensitive. It does not bear 



FIG. 37 FIG. 38 FIG. 39 



changes in position very well, and I have been able to 

 demonstrate positive geotropism only in newly grown 



1 Part I, p. 176. 



