Plants as Affected by Excessive Food. 151 



ively moist atmosphere. Orchards too closely planted or 

 surrounded by wind barriers suffer more from fungous 

 attacks than those having freer circulation of air be- 

 tween the trees. i 



246. InsuiHcient Wind Promotes Damage from Frost 

 by permitting cold air to settle in the lower places 

 (209). On these accounts, gardens and fruit plan- 

 tations should not be entirely surrounded by wind 

 barriers. 



247. Pollination (150) is Dependent upon Wind in 

 many plants, as the coniferous trees, oaks, elms, birches 

 and sedges; but as the pollen of such plants is very 

 light, their fruitfulness is not often much restricted by 

 insufficient wind. 



Section VI. Pl.lnts as Affected by Unfavorable 

 Food Supply. 



We saw that water is the. most important constituent 

 of plant food (62) and we have already considered the 

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

 a proper supply of the other essential food constituents 

 is only second in importance to that of water. 



A — Plants as Affected by Excessive Food. 



248. 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 meth- 

 ods. Indeed, nearly all of the censtituents of plant food 

 may be present in excess of the requirements of plants 



