THE INHIBITORY ACTION OF APICAL LEAVES 



101 



diction with the theory of polarity at which we arrived in the 

 preceding chapter. 



The second is that the inhibitory action of the descending 

 sap from the leaf on shoot formation in the basal part of the stem 

 is an indirect one and due to the fact that this sap is either con- 

 sumed entirely for the growth of the stem in length or in thickness 



J^iG. 79. — In old stems the apical leaves no longer inhibit shoot formation below. 



and that for this reason none or too little of the material con- 

 tained in the descending sap is available for shoot formation; 

 or that the rapid growth of certain parts of the stem attracts the 

 sap from the anlagen for shoots in this region and thereby inhibits 

 shoot formation; or that this rapid growth of the stem inhibits the 

 shoot formation indirectly in some other way. Such an explana- 

 tion would be in harmony with the theory of polarity of regenera- 

 tion given in the preceding chapter. These phenomena of 



