183 LECTURES ON 



These general principles are the following: 



1. Plants require various kinds of fixed mineral matters, and derive 

 the same exclusively from the soil. 



The only exceptions to this statement are, perhaps, to be found in 

 case of chlorine and sodium, which appear to be carried inland from 

 the sea in the direction of prevailing winds, both in the spray and 

 dissolved in the vapor that ascends from the ocean. 



2. Some plants which, in the natural state, derive a large portion of 

 the volatile elements of their structure — viz: carbon, hydrogen, oxygen, and 

 nitrogen — from the air, must be supplied with much more of these matters 



from the soil, in agricultural production. 



As already remarked, the increased supply of these matters by the 

 soil is requisite only to insure that rapid and abundant growth which 

 constitutes agricultural production. 



The very fact of an artificially increased supply of food to plants, 

 in connexion with the care otherwise provided by cultivation, in a few 

 generations enlarges their capacity for assimilating nutriment, greatl} 7 " 

 increases the mass of vegetable matter that can develop on a given 

 surface, and, in consequence, makes a fertile soil necessary for exhib- 

 iting the capabilities of the crop. Many of our agricultural plants are 

 the result of high cultivation, including, as one of its most efficient 

 factors, a fertile, and, in most cases, artificially fertilized soil. The 

 wretched weeds from which our numerous varieties of turnip, ruta- 

 baga, kohl rabi, cauliflower, broccoli, and cabbage have been derived, 

 are hardly recognizable as the originals of so many useful plants, 

 and these, as well as the wild egilops of southern Europe, from which 

 the wheat grain appears to have come, are no less inferior to the cul- 

 tivated plants, in appearance and value, than is the soil required for 

 their natural development, to that demanded in their agricultural pro- 

 duction. 



3. Different plants require different proportions of these substances for 

 their luxuriant growth. 



4. Different plants require different absolute quantities of food to ma- 

 ture a full crop. 



These propositions are illustrated by the accompanying table, 

 which represents, in average figures, the weight, in pounds, of total 

 produce, and of the chief ingredients, removed annually from an acre of 

 good land, in case of several of the more commonly cultivated crops. 



