110 ON THE FOOD OF PLANTS. 



" manure. This celebrated horticulturist lived, 

 " however, sufficiently long to alter his opinion. 

 '* The results of his later and more refined ob- 

 * c servations led him to the conclusion, that no 

 " single material afforded the food of plants. 

 " The general experience of farmers had long 

 " before convinced the unprejudiced, of the truth 

 " of the same opinion, and that manures were 

 " absolutely consumed in the process of vegeta- 

 " tion. The exhaustion of soils by carrying off 

 " corn crops from them, and the effects of feed- 

 " ing cattle on lands, and of preserving their 

 " manures, offer familiar illustrations of the prin- 

 " ciple. And several philosophical enquirers, 

 " particularly Hazenfraz and Saussure, have 

 " shown by satisfactory experiments, that ani- 

 " mal and vegetable matters deposited in soils 

 " are absorbed by plants, and become a part of 

 " their organised matter. But though neither 

 " water, nor air, nor earth, supplies the whole of 

 " the food of plants, yet they all operate in the 

 " process of vegetation. The soil is the labora- 

 " tory in which the food is prepared. No ma- 

 " nure can be taken up by the roots of plants 

 "unless water is present j and water, or its 

 " elements, exist in all the products of vegeta- 

 " tion. The germination of seeds does not take 

 " place without the presence of air or oxygene 



