Plants as Affected hy Insufficient Food. 147 



long as stable manure is used (252). But the more con- 

 centrated animal manures, as those from poultry and the 

 hog, the chemical compounds of nitrogen, as nitrate of 

 soda and sulfate of ammonia (262), and the so-called 

 "high-grade" commercial fertilizers must be used with 

 caution, as they may destroy the plants if applied in 

 excess. 



B — Plants as Affected by InsufI'Mcient Food 



251. It is difficult to st-parate 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 (63). But 

 even with a proper water supply, if one or more of the 

 requisite food materials is lacking (61j, a normal plant 

 structure cannot be built up. An excess of one food sub- 

 stance cannot compensate for the lack of another, except in 

 a few instances. 



252. Insufficient Food Dwarfs the Plant in all its parts. 

 A dwarfing of the sLe of the plant body may occur, how- 

 ever, without a corresponding dwarfing of tlic seed pro- 

 duct; hence plants may often bear their maximum amount 

 of seed or fruit without attaining their maximum dimen- 

 sions. 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 restric- 

 tion 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 fertilizing components of the 



