THE WATER OF THE HABITAT 



15 



MODIFYING FACTORS 



20. Influence of soil upon water content. The soil of a habitat 

 is of the greatest importance in determining the amount of water 

 content, and also the kind of water, i.e., the chemical substances 

 found in solution. The amount of water present is directly de- 

 ' pendent upon the texture or fineness of the soil, that is, upon 

 its physical properties. The kind and amount of nutrient mate-' 

 rial dissolved in the water are determined by the chemical nature 

 of the soil. Tn studying the influence of the latter, it is conse- 



FiG. 2. Glacial boulders at Lake Moraine, below Pike's Peak, in \\hich 

 the disintegrating action of weather is aided by the roots of trees. 



quently necessary to examine the physical structure and to deter- 

 mine the chemical composition. These are not of equal value, 

 however. The amounts and kinds of soluble materials in all ordi- 

 nary habitats are so nearly alike that differences in chemical com- 

 position are of little importance. They play a large part only 

 where soluble chemical compounds are i)resent in excessive amomits, 

 as in alkaline soils, or when the amount of humus is unusually 

 large or deficient. An excess of soluble salts hinders absorption 



