JACQUES LOEB 305 



We selected for each experiment twelve pairs of sister leaves and 

 care was taken that the leaves were healthy, not too large, and of 

 equal size. We made sure that the fresh weight of each set of 

 leaves with their piece of half stem was approximately hke that of 

 the set of sister leaves (Table V). 



The difference in one set is not more than 3 per cent and is equalized 

 by the fact that six sets of different experiments were made. We 

 proceeded then as follows. The dry weight of b (Fig. 4) was ascer- 

 tained immediately. Then the leaf a (detached from its stem) and 

 the leaf ai (in connection with its piece of half stem) were suspended 

 in the same aquarium dipping with their apices into water. In the 

 leaves a (without stems), roots and shoots formed soon, while none, 

 or practically none, formed in leaves ai. 



TABLE V. 



After several weeks the shoots were cut off, their dry weight was 

 determined, and the piece of stem &i was also detached from it's leaf 

 and its dry weight determined. Let a be the dry weight of shoots 

 and roots formed by the leaves detached from their stem; let ai be 

 the dry weight of shoots and roots formed by the leaves or in the 

 axil of the leaves connected with their stem; let b be the dry weight 



shoot formation the more completely the smaller the leaf. When the leaf is 

 large it furnishes more material than the cells of a small piece of stem can absorb. 

 It is also of interest that the inhibitory power of a piece of stem on shoot forma- 

 tion in a leaf is smaller in an old leaf than in a young leaf nearer the apex. This 

 influence of age of the leaf is probably connected with the fact that in the oldest 

 leaf the flow of sap into the leaf is more or less incomplete; this interruption of 

 sap flow may possibly be the first step in the histological changes at the base of 

 the leaf which cause it to fall off. In our experiments conditions were selected 

 in such a way as to make the inhibition of shoot and root formation in Leaf oi 

 practically complete. 



