199 



vessels. — We may observe too, that the 

 bark of trees, which grow sheltered, is 

 thin ; and hence, the sap-vessels are near 

 the surface ; of course, many of them may 

 suffer from exposure. — AVe know, besides, 

 that heat is absolutely necessary, not only 

 to put vegetation in motion, but to keep 

 it so; and therefore, its increase will always 



be effected by the degree of heat.- We 



may observe, also, that furious winds never 

 fail to damage the leaves of trees, in pro- 

 portion to their flexibility.— And, there- 

 fore, in this warfare, the youngest natu- 

 rally suffer most ; which is peculiarly 

 unfortunate, because they are the princi- 

 pal agents in forwarding the business of 

 vegetation. On the whole, it is presumed, 

 much of the damage done by sudden ex- 

 posnre, may be naturally traced to the 

 above causes. But whether such be the 

 case or not, the effect is exactly as stated, 

 and the means of prevention the same ; 

 namely, thinnings and afterwards j?r//w/?/ov 

 gradually. 



