AMERICAN SYLVICULTURE 



intensity and rapidity of water obtention and retention. Sand, 

 for instance, allows water to enter into its large pores quickly, but 

 gives it up rapidly as well. Wet, moist, fresh, dry and arid soil 

 are distinguislied. 



The degree of the wetness of the soil is of the utmost impor- 

 tance for tree growth. At its Southern limit, a species may grow 

 but along watercourses. The water in the soil dissolves the mineial 

 salts and seems to be of great influence on the bacterial life in 

 the soil. 



iX. Heat in the soil. 



It is derived from the earth's own temperature, from chemical 

 processes in the soil (notably fermentation) and from the sun rays. 

 In the latter case, the angle of insolation, the duration of insolation, 

 the heat capacity, the color, the porosity of the soil and its 

 vegetable cover serve as influencing factors. 



A cold root has no pumping power. Fine root fibres die from 

 temperatures which fine oranches easily withstand. The actual 

 influence of the heat in the soil on tree gi'owth is practically un- 

 known. The opening of the buds in spring and the fall of the 

 leaves in autumn are probably connected with the thermic changes 

 occurring in the various strata of the soil. 



X. Depth of soil. 



Flat rooted species easily obtain the superiority over tap- 

 rooted species on shallow soil. Tree roots, however, are not apt 

 to penetrate to a depth greater than six feet. Shallow soil in- 

 creases danger from fire, drought, storm. A tap rooted species, 

 planted on shallow soil, produces but a stunted form. Shallow 

 soil is well adapted to the coppice system, in case of broad leaved 

 tap rooted species. 



XI. Food in the soil. 



A tree, like a crystal, is composed of various chemical elements. 

 The available amount of that necessary element which happens to 

 occur in the relatively smallest degree determines, in both crystal 

 and plant, the rate of growth actually taking place (Liebig''s law). 

 The superabundance of one component, even of a necessary com- 

 ponent, prevents, on the other hand, the local existence of many 

 species. 



The ten necessary elements found within a plant in solid, liquid 

 or gaseous condition are 0, H, C, P, Fe, K, Mg, Ca, N, S, 



" Roots search food as if they had eyes," is a rule easily proven 

 in any nursery. 



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