THE ART OF THE SECOND GROWTH 



have yielded, however, the astonishing result that winged seeds 

 travel much more slowly than heavy seeds coveted by birds. Fliche 

 gives the following number of years as required by trees traveling 

 from Nancy to Paris, a distance of 160 miles: 



Beech 18640 years. 



Chestnut 12920 years. 



Pine 48G80 years. 



Sarvis 1330 to 2000 years. 



VI. Structure of soil. 



Soil consists of natural rock; or of rock disintegrated under 

 the influence of water, frost, heat, oxygen, carbonic acid, lichens, 

 bacteria; or of material deposited by water, wind or glaciers. 



The components of soil are: 



a. Soil skeleton, large grains, principally quartz and stones. 



b. Soil flesh, minute semi-soluble particles, — the mud of the rivers. 



c. Soil fat, the humose particles giving the soil a dark color. 



d. Soil blood, the air and water, filling the pores of the soil. 

 The size of the pores determines the capillary capacity. 



According to the resistance which soil off'ers to spade or plow, 

 we distinguisli the following classes: 

 Light soil; 

 Loose soil; 

 Binding soil; 

 Heavy soil; 

 Stiflf soil. 



VII. Air in the soil. 



Roots require oxygen for breathing. Like fish, they die from a 

 lack as well as from a superabvmdance of oxygen. Subterranean 

 air is rich in carbonic acid exhaled by roots, fungi, bacteria, 

 animals. Swamp soil contains little air. Hence no species find a 

 living in swamps but those which have large inner air ducts. 



Prairial soil is naturally so compact that it contains little 

 oxygen. 



VIIL Water in the soil. 

 It occurs: 



a. Chemically bound to minerals and salts. 



b. Absorbed by the hygroscopicity of the soil. 



c. Raised by the capillary power of the soil. 



d. As ground water, — lakes, swamps, brooks being merely areas 



of open ground water. 

 The size of the pores and the presence of humus govern the 

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