On the Theory of Vegetation. 17D 



been considered in this light by rational enquirers after 



■i 



truth. But I question whether the true princij)les of ve- 

 getation may not furnish more useful and important lessons 

 to our farmers than even philosophers generally imagine. 



It is a well known fact that many vegetables, as clover, 

 peas, beans, and vetches, help to fertilize exhausted feelds, 

 especially \i i:)lowed in, as the farmers call it. But I cannot 

 find that the true reason of this effect is generally under- 

 stood. I wish if possible to diffuse a knowledge of the cause, 

 in full confidence that the principle may be ap2)lied to ma- 

 ny beneficial purj)oses in agriculture. 



Vegetables, when analized, are found to consist of water, 

 earth, oil and salts. It seems to be the generally received 

 opinion among philosophers, that the cementing principle, 



by which the component parts of vegetables are held togeth- 

 er, is fixed air. With these substances there is united a por- 

 tion of phlogiston ; but the parts which contribute most to 

 fertility are oil and salts. Now it is agreed among the lern- 

 ed, that vegetables are furnished with inhaling or absorbing 

 pores, and that the pores of the leaves and branches serve 

 the double purpose of alternately inhaling and exhaling, 

 according to the temperature of the atmosphere. All this 



V 



is admitted by modern philosophers, yet they contend that 



+ 



vegetables derive their principal nurrishment from the earth. 

 It appears to me this cannot be true in the extent it is com- 

 monly supposed; for if true, I do not see how vegetables 

 of any kind should enrich the land on which they grow, 



apidly as some of them do 



A crpp 



