ON THE FOOD OF PLANTS. 1^7 



that plants throw oft' anything as excrementitious 

 but oxygene ; and consequently, if nitrogene is 

 taken in, it must be appropriated. This remark 

 also applies to the consumption of hydrogene. 

 If a plant be induced to consume an extra quan- 

 tity of hydrogene, or carburetted hydrogene, it 

 must form a surface sufficiently large to employ 

 or appropriate it, or it must be passed off" as 

 diseased excresence ; it cannot be expelled in a 

 healthy manner, like oxygene. 



Sir Humphry says, " In the writings of scien- 

 " tific agriculturists, a great mass of facts may 

 ** be found in favour of the application of farm- 

 " yard dung in a recent state. Mr. Young, in 

 ** an Essay on Manures, which I have already 

 " quoted, adduces a number of excellent autho- 

 " rities in support of the plan. Many who 

 " doubted have been lately convinced : and, 

 " perhaps, there is no subject of investigation, 

 " in which there is such a union of theoretical 

 " and practical evidence. I have myself, within 

 " the last ten years, witnessed a number of dis- 

 " tinct proofs on the subject. I shall content 

 " myself with quoting that which ought to have, 

 " and which I am sure will have, the greatest 

 " weight among agriculturists. Within the last 

 ** seven years, Mr, Coke has entirely given up 



