108 



REGENERATION 



Two facts have now been proved; first, that the ascending 

 sap sent out by a basal leaf can produce roots in a stem of Bnjo- 

 phyllum and the quantity of roots produced is smaller when the 

 stem is completely defohated than when it has one or two leaves 

 at the base; it can also be stated, though this was not proved 

 quantitatively, that the root formation caused by the basal leaf 

 increases with the mass of the latter. Second, that the descending 

 sap sent out by an apical leaf increases shoot formation in the 

 basal part of the stem and that this shoot formation increases 

 with the mass of the apical leaf. This makes it impossible to 

 attribute the polar character of regeneration in a stem of Bryo- 

 phyllum to differences in the chemical constitution of the ascend- 

 ing and descending sap. The only alternative is, as far as the 

 writer is aware, that the ascending and descending sap reach 

 primarily different kinds of tissues, the ascending sap reaching 

 primarily the anlagen for shoot formation and the descending 

 sap the anlagen for root formation. The fact that the descending 

 sap from an apical leaf inhibits shoot formation and favors root 

 formation in its downward path must be correlated with this con- 

 clusion. It was suggested earlier in this chapter that this inhibi- 

 tion might be the indirect result of a growth of the stem in length 

 or thickness as a consequence of which the growth of shoots is 

 inhibited in the basal part of the stem. 



