MODERN HIGH FARMING. 17 



unaided nature does not with sufficient rapidity replace. It is 

 consequently necessary to artificially introduce it into the soil in 

 some cheap, efficacious and soluble form, if we desire the equilibrium 

 to be undisturbed, since its presence determines the dearth or 

 abundance in the plants of nitrogenous carbon-hydrates or proteids, 

 such as legumine or vegetable caseine in the leguminous species, 

 gluten in the cereals, and nicotine in tobacco. 



As at a later stage of this work we shall come back to this 

 question under the heading of Manures, we may for the present leave 

 the gaseous elements and pass on to those of a mineral nature, which 

 play a no less important part in the vegetable economy. 



