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means, is limited to the acceleration of the de- 

 velopment of the plants under cultivation; 

 and that there are other circumstances vvhicli 

 have a remarkable influence upon the growth 

 of the crops. We will recur to this very im- 

 portant point vv^hen speaking of mineral ma- 

 nures. 



« 



CHAPTER III. 



MINERAL MANURES. 



Plants invariably contain earthy and al- 

 kaline matters, indispensable to their growth 

 and perfect vitality. A single example is suf- 

 ficient to show the necessity of the presence 

 of certain salts in plants. The bony frame of 

 animals owes its stiffness to the phosphate and 

 carbonate of lime, and these calcareous salts 

 must therefore be furnished by the food ; for 

 all aliments are definitively derived from the 

 vegetable kingdom. 



Another evidence of the utility of salts, is 

 the fact that plants do not indifierently receive 

 those which are conveyed to them, but really 

 exercise a power of preference. This pro- 

 perty and the utility of selected mineral sub- 



