CULTURE OF THE GRAPE. 209 



four inches per annum. This is at the rate of 87.120 cubic 

 feet or 2.466 metres of rain-water per acre ; and this, 

 according to the proportions per cubic metre in the pre- 

 ceding table (M. Barrel's), would afford annually of 



" Nitrogen 45 pounds. 



Nitric Acid 103 " 



Ammonia 19 " 



Chlorine 12 " 



Lime 35 " 



Magnesia 11 " 



Amount total per acre 227 " 



" Of these substances, the three first are of the utmost 

 importance, on account of their entering so largely into 

 the indispensable constituents of the food by which vege- 

 table life is sustained. The quantity of ammonia thus 

 ascertained to exist is about what is expected in two 

 hundred- weight of Peruvian guano; and bountiful Na- 

 ture gives us, moreover, nearly one hundred and fifty 

 pounds of nitrogenous matter equally suited to the nutri- 

 tion of our crops." 



True as it may be that there is vast benefit from rain 

 in addition to the humidity which it yields, and that an 

 increased supply promotes luxuriant vegetation, yet there 

 is a limit to the requirements, and also to the capacity, of 



14 



