UNFAVOBABLE FOOD SUPPLY 145 



long, weak straw, with poorly-filled heads. Grape vines 

 on over-manured ground produce excessive wood with 

 few and late-ripening bunches. 



There is little danger of over-manuring, however, with 

 crops grown for parts other than flowers, fruit or seed, 

 so long as decomposed stable manure is used (251). But 

 the more concentrated animal manures, as those from 

 poultry and the hog, the chemical compounds of nitro- 

 gen, as nitrate of soda and sulfate of ammonia (261), 

 and the so-called " high-grade " commercial fertilizers 

 must be used with caution, as they may destroy the 

 plants if applied in excess. 



PLANTS AS AFFECTED BY INSUFFICIENT FOOD 



250. Lack of food and water. — It is difficult to sep- 

 arate the effects of a lack of food from those of a lack of 

 water, since the food is mainly conveyed to the plant in 

 the soil water (62). But even with a proper water supply, 

 if one or more of the required food materials is lacking 

 (60), a normal 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. Dwarfing of plants. — 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 those grown for their 

 leaves, stems, roots or tubers. The cereals, for example, 

 produce well on land not sufficiently fertile to yield equally 



