JACQUES LOEB 



351 



The correctness of this idea is supported by the further fact that this 

 inhibitory effect of a leaf on the growth of shoots, especially in the 

 basal parts of the stem, is diminished when the mass of the leaf is 

 reduced. Fig. 15 shows such an experiment. Of the five stems on 

 the left each had one whole leaf on the upper side of the originally 

 horizontal stem. In one stem only did a shoot form and this shoot 



upper 



Fig. 12. 



Fig. 13. 

 Figs. 12 and 13. Explanation of the influence of gravity on regeneration in 

 horizontally suspended stems on the assumption that inhibition is due to sub- 

 stances carried by the sap sent out by the leaf. When the leaf is below (Fig. 

 12), the buds in Nodes 1 and 3 are at the upper edge of the sap flow and these 

 buds may or may not escape the inhibitory effect. In Fig. 13 the leaf is above 

 and the sap flowing in the upper half is bound to reach the buds in Nodes 1 and 

 3 and hence their growth is necessarily suppressed. The lower Buds 2 and 4 

 are outside the sap flow and may develop. 



