Ill 



above the scars, the descending sap would 

 appear to be necessary to this new growth, 

 if not its sole cause. And in speaking of 

 the growth in diameter of the entire tree. 

 I have taken this/ac/ for granted, though 

 this, like most other physiological ^ac^s, is 

 a possibility based on probability. 



I have observed larch poles, when nailed 

 as rails in the air, without any communi- 

 cation with the earth, throw out twigs the 

 first summer. This would appear to be 

 the result of the elaboration of the upward 

 sap already in the "t^oood. 



If a piece of bark is insulated, new growth 

 will be deposited from the scar of the 

 continent^ but not from the island^ except 

 a very slight deposit the first year from the 

 descending sap already in the bark. But if 

 the island has a twig or branch on it, or if 

 it throws one out, which is very likely, the 

 descending sap from the branch will deposit 

 new growth on the scar round the island. 

 We are to suppose the upward sap 



