^s^o. 474] 



SAP FLOW IN MAPLE 



453 



permeable thus setting up a current and accompanying pressure 

 from the pith toward the bark. 



19. The maple type seems to differ from the birch type prin- 

 -cipally in the locahzation of the active cells mainly in the trunk, 

 rather than in the root; and in the spasmodic action of these under 

 certain stimulation. 



20. It is quite possible that careful research will show no such 

 irritability in the butternut and other trees of this group as is found 

 in the maple. 



