166 MANURE. 



is no reason for assuming, as do some, that carbonic 

 acid, is the only source of the carbon of plants. 

 The volumes of carburetted hydrogen produced in 

 the decay of plants, may be intended as well as 

 carbonic acid for their nutriment. Suppose, of which 

 there is no doubt, that carburetted hydrogen of gly- 

 cerine, contributes to this effect, there remains then, 

 free carbon, which being perfectly insoluble and 

 changeless, acts only by condensing gases in its pores. 



235. Geine, by tillage, air and moisture, evolves 

 also, carbonic acid. As gas, no one will deny that 

 it thus affords carbon to plants ; its carbonic acid is 

 absorbed and its carbon assimilated, and hence, if 

 either glycerine or geine afford carbon, the circum- 

 stances under which they may be applied to the land, 

 are less favorable to the production of carburetted 

 hydrogen, than of carbonic acid. The balance then 

 is in favor of geine. 



236. There are two circumstances, wherein geine 

 and glycerine differ. The latter is soluble to any 

 extent in water, it is applied to the land in spent 

 ley, already dissolved. The action so evident, is 

 due to one of two causes, or to their joint action. 

 Spent ley, acts either by its organic, or by its inor- 

 ganic part, by its glycerine, or by its salts. Those 

 who take the ground, that humus or geine, never is 



