MEDIUM AND SPACE FOR GROWTH. 61 



I. Proper medium and space for groivth. In the process 

 of germination, the only conditions are air, water, and a cer- 

 tain temperature. But as soon as the roots and stalks make 

 their appearance, they require mechanical support, and a 

 medium for the action of those agents which are necessary to 

 their perfect development. This medium is the soil and the 

 atmosphere. The former only demands attention in this 

 connection. There are some aquatic plants that float upon 

 the surface of water and derive their nourishment from it, and 

 from the atmosphere; and a large number of parasitics, as 

 the mistletoe, which attach themselves to larger plants or 

 trees, and even to the rocks, such as the mosses, from which 

 they derive support and nourishment ; but all vegetables, cul- 

 tivated for the use of man, and other animals, require, as a 

 necessary condition to the most vigorous action of their vital 

 powers, that their roots should he fixed in the soil. 



Uses of the Soil The soil appears to serve several pur- 

 poses in this respect. 



1. It furnishes support to the plant, and prevents it from 

 being blown about by the winds. Different plants require 

 different kinds of soil to give the requisite stability. Wheat 

 requires a stiff soil ; corn a light one. This results, not only 

 from the different degrees of strength in the vital power, but 

 also from the character of the roots, and the weight which 

 the stalk must sustain. Those roots which lie near the sur- 

 face, like most of our common grains, require a stiff soil ; 

 those which penetrate deep, like most of the hoed crops, re- 

 quire a light soil in order to gain the requisite support ; hence 

 the importance of adapting the crop to the character of the 

 soil, or the soil to the nature of the root. 



2. The soil is the repository of the food of vegetables, and 

 a medium of communicating it to their roots. 



3. The soil facilitates the chemical changes, necessary in 

 the preparation of the food, and of those saline compounds, 

 which either act as a stimulus to the vital power, or are the 



