Plants as Affected by Insufficient Food. I4I 
compounds of nitrogen, as nitrate of soda and sulfate of 
ammonia (262); and the so-called “ high-grade” commercial 
fertilizers must be used with some caution, for if applied in 
excess they may destroy the plants. 
B—THE PLANT AS AFFECTED BY INSUFFICIENT Foop 
251. It is difficult to separate 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 requisite food 
materials (61) is lacking, a normal plant structure cannot 
be built up. An excess of one food substance cannot compen- 
sate for the lack of another, except in a few instances. 
252. Insufficient Food Dwarfs the Plant in all its 
parts. <A dwarfing of the size of the plant body may occur, 
however, without a dwarfing of the seed product; hence plants 
may often bear their maximum amount of seed or fruit with- 
out 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 good 
crops of tobacco, cabbage, celery, lettuce or potatoes. But 
with a sufficient restriction of food, the seed product will 
suffer diminution, or be wholly cut off. 
253. Crop-Growing Tends to Reduce Plant Food in 
the soil in proportion as the crops are removed from the 
land, and are not returned to it,‘directly or in equivalent. 
Fortunately, a very considerable amount of plant food is 
constantly being liberated by the disintegration and decay 
of rock or soil materials, or is being deposited from the at- 
