WHEAT 41 



favorable degree of heat. The plantlet is nour- 

 ished at first by the food substance,, stored in the 

 mother seed, but this is soon used up and the 

 little roots quickly spread out in the prepared 

 soil to gather the moisture and available plant 

 food which may be found there. The young plant 

 grows and is soon well established if the soil is 

 fertile and the seed bed has been well prepared. 



HOW PLANT FOOD IS MADE AVAILABLE 



All fertile soils contain an abundant supply of 

 plant food elements, but the compounds in which 

 they exist are usually in an insoluble condition in 

 the soil, a provision of nature which prevents the 

 wasting of plant food, insures the permanency of 

 soil fertility and the continued productiveness of 

 the soil for ages, providing man does his part. 



The plant food of the soil is gradually liberated 

 by the action t of weathering agents which cause 

 the rock particles to break down and disintegrate, 

 and is made available by the action of the soil 

 bacteria which assist in the processes of decay. 

 Thus chemical changes take place by which the 

 insoluble plant food is gradually changed into 

 soluble compounds, the elements of which become 

 available to the plants when absorbed by the 

 roots. 



This "digestion" of the plant food in the soil 

 by which it is made available to plants, at least 

 so far as bacteria are concerned, is favored by the 

 same conditions which are essential for the 

 germination of seeds and the growth of plants, viz., 

 the soil must be warm, moist and well aerated. 



