146 Prlncqjles of Plant Culture. 



Section VI. Plants as Affected by Unfavor- 

 able Food Supply 



AVe saw that water is tlie most important constituent 

 of plant food (63) and we have already considered the 

 plant as affected by water supply (Section III). But a 

 proper supjily of the other essential food constituents is 

 only second in importance to that of water. 



A — PIjAN'ts as Affected by Excessive Food 



249. Excessive food is not the extreme that we have 

 most to fear, since natural soils are rarely excessively 

 fertile, and we can only make them so by costly methods. 

 Indeed, nearly all the constituents of plant food may be 

 present in excess of plants' requirements without work- 

 ing harm. Nitrogen, however, which aside from water 

 is the most potent food constituent, must be used with 

 some discretion. 



250. Excessive Nitrogen Stimulates Growth at the ex- 

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

 these parts, therefiyre, fertilizers rich in nitrogen must be 

 used with caution. Ai)ple, itear and quince orchards 

 liberally manured witlr such fertilizers jjroduce an ex- 

 cessive, over-succulent growtli of wood, that is subject 

 to blight and winter injury and forms comparatively few 

 fruit buds. Grain under similar conditions forms long, 

 weak straw, with ijoorly-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 

 croi^s grown for parts other than flowers, fruit or seed, so 



