LETTER IV. 



35 



the height and thickness of the aggregate remains of 

 the plants ; and thus also, while the roots of the plants 

 of each succeeding year, extending beyond those of the 

 preceding, strike into new and fresh soil, is the basis 

 of sustentation under ground proportionally widened 

 and strengthened. Fig. l. 



8. As yet I have said no- B 

 thing as to the hark and its 

 disposition. A fresh layer of 

 this is formed annually in 

 connection with the plants of 

 each year ; and if our theory 

 be correct, the successive an- 

 nual layers will be disposed 

 in accordance with its re- 

 quirements. And such is 

 actually the case. The woody 

 stem and root of each seed- 

 ling tree-plant is everywhere 

 invested on its exterior with 

 a coating of bark, as in figure 

 1, A. But how do the bark 

 and root of the next year's 

 plant comport themselves in 

 relation to the wood and 

 bark of this seedling, on the 

 summit of which it grows ? 

 By the theory they ought to press down wedgewise 



A 



