152 Principles of Plant Culture. 



out working harm. Nitrogen, however, which aside 

 from water is the most potent food constituent, must 

 be used with some discretion. 



249. Excessive Nitrogen Stimulates Growth at the 

 expense of flowers, seed and fruit. In crops grown for 

 these parts, therefore, fertilizers rich in nitrogen must 

 be used with caution. Apple, pear and quince or- 

 chards liberally manured with such fertilizers produce 

 an excessive, over-succulent growth of the wood, that is 

 subject to blight and winter injury and forms compara- 

 tively few fruit buds. Grain under similar conditions 

 forms 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. 



B — Plants as Affected by Insufficient Food'. 



250. 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 required food materials is lacking (60), a nor- 



