333 



CHAPTER IX. 



COMPOSITION OF PARTICULAR CROPS AND MANURES. 



904. Plants diiFer considerably from each other 

 in chemical composition ; not only do various plants 

 consist of different proportions of the proximate ele- 

 ments which compose them, but also the same plant 

 is found to contain variable proportions of these sub- 

 stances, depending on the peculiarities of soil, situa- 

 tion, mode of cultivation, manure, and the weather, 

 or season when they were grown. In the following 

 pages a brief account is given of the average mean 

 composition of some of the principal plants which are 

 cultivated as crops. 



905. The first point to be ascertained is the relative 

 proportion of water, organic matter, and inorganic 

 matter in different plants. This is done by very 

 carefully drying a weighed portion ; the loss which 

 it sustains indicates the quantity of water. The dry 

 matter is then burnt, the weight of the ashes shows 

 the proportion of inorganic matter. The chemical 

 composition of the organic matter, as well as the in- 

 organic constituents, requires a separate analysis. 



