CH. v.] THE SAP. 169 



matter is formed that unites it to the stock. A con- 

 fused line marks the point of union, but all the 

 deposit of wood is between that line and the bud, 

 and is always the same in character as the tree 

 from which the bud is taken. 



A bud, with almost the solitary exception of that 

 of the walnut, succeeds best when inserted on a 

 shoot of the same year's growth, and apparently 

 for the reason that the sap and juice it yields are 

 most nearly of the same state of elaboration as they 

 were in the parent of the bud ; and because, as 

 in the animal frame, repair of injuiy, the healing of 

 wounds, is always advanced most favourably by the 

 \^tal energy of youth. 



The more mature any part of a plant the less easy 

 is it excitable ; a branch from which the leaves have 

 fallen in autumn requires a higher temperature to 

 induce vegetation, than does a similar branch in the 

 spring. So is it with a bud ; and, as was suggested 

 by Mr. Knight, it appears to be occasioned by those 

 parts having passed into a state of repose ; a de- 

 creased degree of ^'ital energy occurring preparatoiy 

 to their -winter sleep. Let no man scoff at the idea 

 of this vital energy continuing in a bud after a sepa- ^ 

 ration from the parent, for even the head of a poly- 

 pus may be cut off and grafted, ^\'ithout injuiy, upon 

 the decapitated body of another. The mature bud 



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is consequently always inserted with more success f^i, ^ 



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