96 



REGENERATION 



on that side of the stem where the leaf is, while on the opposite 

 side which is not reached by the descending sap from the leaf a 

 shoot can form. The two buds in the first and third node below 

 the leaf, being in the path of the descending sap from the leaf, 

 are prevented from growing while the bud in the second or fourth 

 node below (Fig. 72) but opposite the leaf is outside the path 

 of the descending sap from the leaf and can therefore develop. 



Fig. 72. — Young stem with one apical leaf. Bud opposite the leaf (in node 0) 

 is cut out. Shoot formation in the first node below the leaf is suppressed, but 

 a shoot is formed in the second node below and opposite the leaf. 



That the descending sap from a leaf inhibits shoot formation in 

 young stems is further supported by the fact that when the size 

 of the apical leaf is sufficiently reduced the inhibitory effect 

 of the leaf on shoot formation ceases, and that shoots can now 

 grow out in the first node below the leaf (Fig. 73). And finally, 

 if half of the base of the petiole of the apical leaf (where it joins 



