100 



REGENERATION 



anlagen which he a httle more on the side. This is clearly illus- 

 trated in experiments on old stems split longitudinally and 

 possessing one apical leaf (Fig. 78). In this case the shoots in the 

 first and third node below the leaf can grow out but not the shoot 

 in the second node below the leaf, because the latter is in the 

 middle of the path of the descending sap from the leaf while the 

 other buds are only on the side. 



Fig. 78. — Old stem split longitudinally, one leaf at apex. In this ease shoot 

 formation occurs in first and third node below the apical leaf, but not in the 

 second node below the leaf. Oct. 24 to Nov. 13. 



2. These experiments leave no doubt that the sap sent out by 

 an apical leaf in the descending current of sap inhibits the shoot 

 formation in the parts of the stem below the leaf which lie in the 

 path of the descending sap; provided the stems are suspended 

 vertically and are young (less than one year old). There are, 

 as far as the writer is aware, two ways of accounting for this 

 inhibitory action of the descending sap from the leaf on shoot 

 formation below. The first is that the descending sap contains 

 some specific hormone which directly suppresses shoot formation 

 and favors root formation. This idea is, however, in contra- 



