CHAPTER I. 



ABSORPTION OF LIQUID NUTRIMENT. 



1. Food of Plants. Green plants generally derive their food 

 from simple chemical compounds in the soil, air, and water. 

 Of these compounds the simple mineral salts are obtained 

 from the soil. Animal manures and decaying vegetable mat- 

 ter do not serve directly as food-material. Elements and 

 simple compounds liberated by the decomposition of these 

 substances may be used in building up the plant. The chief 

 value of such " organic " matter to the plant lies in the fact 

 that it preserves the porous condition of the soil, thus allow- 

 ing access of air to the roots and retaining water containing 

 nutrient salts in solution. The decaying " organic " material 

 in the soil also furnishes the proper conditions of growth for 

 the soil Bacteria, whose activity is a necessary factor in the 

 development of many of the higher plants. An admixture 

 of " organic " material with the mineral elements of the soil 

 is also a means of equalizing the temperature. 



Aquatic plants in general use the same food-material as 

 land plants. The water in which they grow is in contact 

 with the soil and contains all of its soluble salts in solution. 



Remark. It is to be noted that the species comprised in the parasitic, 

 saprophytic, and insectivorous plants, many of which are furnished with 

 chlorophyll, are able to use directly complex substances derived from plants 

 or animals, and do not depend entirely, or at all, on the simple compounds 

 in the soil. 



2. Nutrient Elements. In order to determine what elements 

 enter into the food of plants, and the office of each substance, 



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