280 THE FARMER OF TO-MORROW 



in soils that had not grown "tired" of these 

 plants, they could not find them. Apparently 

 they did not exist. Apparently they were the 

 product of the growing plant or the product 

 of the soil in its process of functioning to pro- 

 duce this plant. 



If these substances really were the "poison 

 of fatigue," as applied to wheat and cow-peas 

 respectively, a demonstration of the truth 

 ought to be simple enough. A soil solution, 

 either extracted from a healthy soil or put 

 together synthetically in the laboratory, was 

 treated with an "injection" of the "poison" 

 isolated from the soil that was sick of growing 

 cow-peas. Then cow-pea seedlings were intro- 

 duced. Ordinarily these grow well in water. 

 But they did not grow at all in the water which 

 had been treated with "poison." 



The same result was obtained with wheat 

 seedlings, in a solution treated with the wheat 

 "poison." 



On the other hand, cow-peas grew well in 

 the solution inhibitory to wheat, and wheat 

 grew well in the solution that would not grow 

 peas. Apparently the poison was peculiar to 

 each family, inhibitory only to its own family 

 of plants. 



