JACQUES LOEB 



341 



the apical leaf are in the path of the sap flow from the leaf, the 

 formation of shoots is suppressed in these buds, while the bud in 

 the second and fourth nodes below but on the opposite side from 

 the leaf lies outside of the path of the conducting vessels from the 

 leaf. Hence if any bud in such a stem grows out it is usually the one 

 in the second node below but on the opposite side from the apical leaf. 

 As soon as this bud grows out it will inhibit the growth of the 

 lower buds in the same half of the stem. 



Fig. 4. Diagram explaining this inhibitory influence of the leaf on the theory 

 that the descending sap from the leaf carries inhibitory substances. The re- 

 gion of the stem reached by the sap from the leaf is shaded and in the shaded 

 part regeneration of shoots is inhibited. 



The petiole of a leaf is attached with its base to one-half of the 

 circumference of the stem. When we cut off half of the base of the 

 petiole of a leaf, the sap sent out by that leaf can flow only through 

 one quadrant of the next internode. This should limit the inhibitory 

 influence of such a leaf to this quadrant of the node below, and this 

 turns out to be the case. The top of a number of potted plants was 

 cut ofi and only one leaf was left at the apex (Fig. 5). Half of the 



