ON THE FOOD OF PLANTS. 143 



" ferment ; they cannot, therefore, if intended 

 " for manure, be used too soon after their 

 " death." 



" When green crops are to be employed for 

 " enriching a soil, they should be ploughed in, 

 " if possible, when in flower, or at the time the 

 " flower is beginning to appear ; for it is at this 

 " period that they contain the largest quantity 

 " of easily soluble matter, and that their leaves 

 " are most active in forming nutritive matter ; 

 " green crops, pond weeds, the paring of hedges 

 " or ditches, or any kind of fresh vegetable 

 " matter, requires no preparation to fit them for 

 " manure ; the decomposition slowly proceeds 

 " beneath the soil ; the soluble matters are gra- 

 " dually dissolved, and the slight fermentation 

 " that goes on, checked by the want of a free 

 " communication of air, tends to render the woody 

 " fibre soluble, without occasioning the rapid 

 " dissipation of elastic matter." 



This doctrine is evidently founded on the 

 notion, that plants consume vegetable substances 

 in their compound state ; but having admitted 

 that carbon, oxygene, and hydrogene, with a 

 portion of earth, are all the elements that are 

 necessary to compose a vegetable ; and also, that 

 water contains all those elements in itself, ex- 

 cept carbon, and that carbon, produced by the 



