Plants as Affected by Insufficient Food. 153 



of the required food materials is lacking (60), a nor- 

 mal plant structure cannot be built up. An excess of 

 one food substance cannot compensate for the lack of 

 another, except in a few instances. 



251. Insufficient Food Dwarfs the Plant in all its 

 parts. A dwarfing of the size of the plant body may 

 occur, however, without a corresponding dwarfing of 

 the seed product; hence plants may often bear their 

 maximum amount of seed or fruit without attaining 

 their maximum dimensions. Plants grown for seed or 

 fruit are, therefore, less likely to be restricted in yield 

 by insufficient food than these grown for their leaves, 

 stems, roots or tubers. The cereals, for example, pro- 

 duce well on land not sufficiently fertile to yield equally 

 good crops of tobacco, cabbage, celery, lettuce or pota- 

 toes. But with a sufficient restriction of food, the seed 

 product will suffer diminution or be wholly cut off. 



252. Crop-Growing Tends to Reduce Plant Food in 

 the soil in proportion as the fertilizing components of 

 the crops are removed from the land and are not re- 

 turned to it, directly or in equivalent. Fortunately, 

 considerable plant food is constantly being liberated by 

 the disintegration and decay of rock or soil materials, 

 or is being deposited from the atmosphere in rain or 

 snow, so that it is impossible to exhaust the soil of 

 plant food, even with the most improvident culture. 

 But the cultivator should aim at the largest returns 

 from his soil, and these are impossible without restor- 

 ing certain materials that continued crop-removal in- 

 variably reduces below the limit of profitable yields. 



