ON SOILS. 29 



the wheat is concerned, the earth is, by the dis- 

 integration of the original matter of the soil, 

 again acquiring a supply of those salts and 

 phosphates, during the growth of the beans; 

 and this, with the manure which is applied, is 

 sufficient to furnish a supply for the w^heat in 

 the succeeding season. In addition to this the 

 excrement of the one may furnish the pabulum 

 for the other, and thus each has a beneficial ef- 

 fect on the succeeding crop. 



Experience also has taught us, that beans 

 alone are not a sufficient food for horses. It is 

 customary always either to w ix chaff, or gene- 

 rally bran with the beans, to supply the neces- 

 sary amount of phosphates required by the 

 horse for supplying the waste of the body ; and 

 thus chemistry explains and confirms the po- 

 licy of this mode of treatment which long ex- 

 perience only has taught. 



Decaying animal and vegetable matters is 

 also another and a very fertile source of the 

 supply of nutriment to plants — and all soils 

 contain more or less of this matter in some 

 state or other — but the consideration of the 

 immediate effects produced on vegetation by 

 these substances, is likewise postponed until 

 its effects are explained in a succeeding chap- 

 ter; their presence is only noted here as form- 

 ino^ one of the principal constituents of the 

 soil. 



From the remarks we have already made, it 



will be evident that no plants which require 



the same substances for their support can be 



successfully cultivated, either together or in 



4 



