702 



PHYSIOLOGICAL BASIS OF POLARITY. II 



development of roots in the leaves suspended sidewise was explained 

 as being due to a greater collection either of water or of solutes or of 

 both in the notches on the lower side.^ This influence of gravity on 



Apex in water 



Fig. 13. Four leaves dipped with their apices in water whereby the develop- 

 ment of roots is accelerated in the apex. As a consequence the growth of roots 

 in the upper notches of the leaves is inhibited. Duration of experiment 17 days. 



Fig. 14. Sister leaves of those in Fig. 13 suspended in moist air. Most of the 

 notches have roots since the growth is nowhere sufficiently accelerated to retard 

 it in the rest of the notches. Duration of experiment 17 days. 



the collection of water can show mainly in the more fleshy parts of 

 the leaf, i.e. in the middle, but not in the thin tissues of the apex 

 of the leaf. 



