Plants as Affected by Excessive Food. 151 



cessively moist atmosphere. Orchards too closely 

 planted or surrounded by wind barriers suffer more 

 from fungous attacks, than those having freer circula- 

 tion of air between the trees. 



246. Insufficient Wind Promotes Damage from 

 Frost by permitting cold air to settle in the lower 

 places (209). On these accounts, gardens and fruit 

 plantations 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. PLANTS 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. 



i 

 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. Indeeed, nearly all the constituents of plant food 

 may be present in excess of plants' requirements with- 



