90 REGENERATION 



Now if the sap sent out bj^ the basal leaf in the ascending direc- 

 tion is as capable of causing root formation as is the descending 

 sap, we should be able to demonstrate that when a stem possess- 

 ing a pair of leaves at the base is suspended horizontally, roots 

 will also form on the lower side of the stem. That this is the 

 case is shown in Fig. 68. The stem had a pair of large leaves at 

 the base, one of which dipped into water. In order to prevent 

 excessive geotropic curvature the stem was loosely fastened to a 



Fig. 67. — Stem bent passively with convexity on upper side. Roots grow on 

 the lower concave side of the stem. 



piece of wood. Nevertheless some geotropic curvature occurred. 

 The stem has formed no roots on the upper side but an abundant 

 mass of roots on the lower side and some on the sides. The 

 drawing was made on the eleventh day of the experiment. Since 

 the same stem without a leaf would in this time have formed 

 practically no roots on the lower side, the enormous root forma- 

 tion on the lower side of the apical stem must be due to the 

 ascending sap sent out by the basal leaves. The same results 

 were obtained in a large number of experiments though the root 

 formation varies in different stems, especially with the mass of the 

 leaf. But the same is true for the root formation caused by the 

 apical leaf. 



It follows from this that the ascending sap sent out by a leaf 

 gives rise to roots if it reaches cells capable of forming roots; 



