JACQUES LOEB 



695 



earlier date than the root formation; hence the substances existing 

 in the leaf at the time of darkening may suffice for bringing about 

 the geotropic curvature but will not suffice for bringing about ample 

 root formation. 



Fig. 7. Drawing of the same stems as in Fig. 6. 



IV. EJfect of Gravity on Root Formation. 



Figs. 8 and 9 are photographs of whole stems suspended horizon- 

 tally, each stem having an apical leaf on the upper side. All these 

 stems were originally perfectly straight. The reader will notice 

 that all the stems have an abundant supply of roots but these roots 

 are all on the lower side of the stem with the exception of the ex- 

 treme basal end. The mass of the leaves was reduced in one set of 

 stems (Fig. 8) and the mass of roots was less in this set than in the 

 other (Fig. 9), where the mass of the leaves was larger, thus confirm- 

 ing our statement at the beginning of this paper. The stems with a 

 larger mass of leaves have undergone also considerably greater curva- 

 ture than the stems with a smaller mass of leaves. 



