SYLVICULTURE. 



The degree of wetness of soil is of the utmost importance for 

 tree growth. At its southern limit, a species grows only in swamps 

 or along watercourses. The water in the soil dissolves the mineral 

 salts so as to form sap 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 soil (notably fermentation) and from sun rays. In the 

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

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

 vegetable cover serve as influencing factors. 



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

 temperatures which fine branches easily withstand. The actual 

 influence of the .heat in the soil on tree growth is practically un- 

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

 in autumn are probably connected with the thermic changes occur- 

 ring 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 only 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 O, H, C, P, Fe, K, Mg, Ca, N", S. 



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

 in any nursery. 



XII. Species of soil. 



a. Rock. Most important rock formations are: Granite, gneiss, 

 limestone, sandstone, slate and trap. 



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