204 SPRING. 



wood acquires its consistency in the second year, while 

 six or seven are required for the oak. No definitive 

 period can be laid down, however, for every tree depends 

 so much upon the situation and the season. Nor can 

 we even lay it down in a general law, that warm seasons 

 and situations augment the quantity of wood, and cold 

 ones improve its quality, though in native trees the 

 truth be very general. 



When the wood has been completely hardened, its 

 bulk augments no more ; and it is doubtful whether 

 there be in it any power by which it can heal, if 

 wounded. The same holds with bark that has been 

 completely dead. The liber and alburnum have both 

 a healing energy in them, though in the latter it be- 

 comes weaker as the hearty wood is approached. It 

 once was supposed that the whole vegetable action was 

 in the liber, and that the sap, after undergoing some pro- 

 cess in the leaves, formed the new wood in descending ; 

 and that upon that account, when there was a complete 

 section made down to the hard wood, as in the case of 

 lopping off of a large branch, the healing process the 

 production of new bark and wood, by which the 

 wound is in time closed up, took place chiefly at the 

 upper edge of the wound. But that is not the case, 

 as any body that chooses to look at trees that have 

 been pruned may see. The wound begins to granulate 

 always at that place where the bark is in the most 

 sound and vigorous state ; and thus the healing pro- 

 ceeds fastest sometimes from the top of the wound, 

 sometimes from the bottom, and sometimes from the 

 sides, generally indeed from these, and we have never 

 seen an instance of more rapid progress at 'the upper 



