LETTER IX. 



89 



wished to bring you. We have seen what are the 

 more special objects of the existence of vegetables, 

 and what the character and duration of their vita- 

 lity. We have seen also the importance of timber to 

 man, and may infer from this the main object of the 

 existence of trees and tree-plants. And we may now, 

 I think, see a reason why the stems and roots which 

 remain after the fall of the leaves need not, nay, why 

 they should not, any longer retain their vitality. For 

 the chief object of the existence of trees and tree- 

 plants is plainly the production of timber ; and, its 

 production going on by the formation year by year of 

 distinct layers of woody matter, there is a strong 

 presumption, from the considerations now adduced, 

 that on the accomplishment of this object each year, 

 both the timber produced, as well as the plants pro- 

 ducing it, will no longer be either the seat or the 

 subject of vitality. We may thus perceive why the 

 production of our timber-stuffs " need not differ in 

 principle from the production of our " bread-stuffs,'' 

 I say in principle, for there is a difference. It is one, 

 however, in mode only ; a difference in the accidents, 

 not in the essentials of its production, the reason for 

 which also we may readily perceive. For, although 

 for some purposes the wood of the seedling or sappling 

 is useful, yet for most purposes the aggregate collection 

 of the wood of several years successive tree-plants is 

 necessary. Indeed, it is only such an aggregate that 



