180 



On the Tlicori/ of Vcgdailon. 



A crop of clover will fertil 



an exhausted feeld 



the c 



fccld. 



IS 



ed, and the body of 



carried from th 



But if the clover draws the principal part of its 



and salts from the earth, and the most of 



growth 



cut and carried off from the feeld, one w^ould think that 



t 



insted of enriching, it would impoverish the soil. 



The constituent parts of vegetables are contained in 



the 



atmosphere ; and it is rational to suppose that different 



vegetables imbibe more 

 according to their 



or 



less 



nurrishment from the air, 



different 



organization. 



Those 



plants 



which are of a firm texture probably imbibe most of their 

 nurrishment from the earth j as flax and hemp, which re- 

 quire very rich land and impoverish the soil where they 

 grow. But plants which are of a more spongy texture, and 

 whose leaves have larger pores, probably imbibe most of 

 their food from the atmosphere ; as clover, vetches, peas 

 and many other succulent 'plants. This I take to be the 

 reason why the latter enrich the soil where they erow 



& 



es- 



pecially when suffered to rot upon the soil. They imbibe 

 the oily and saline substances from the air, and their vessels 

 serve as tubes to convey them to the earth. 



It may be said, that the particles inhaled by 

 during one part of the day, are 



leaves 



during another part 



But it 



thrown off by perspiration, 

 only the most volatile and 



in this 



fluid part of the nurrishment which is thrown off 

 manner, that is, the water. 



The 



of 



are 



mostlv durin 



J the heet of the day; the process of absorp- 

 tion is principally during the night, and then is the time 



* 



w^hen 



