382 



NATURE STUDY AND LIFE 



may find freshly cut stumps near some of the sections of 

 the soil that they have been studying, and, by counting the 

 annual rings, they may arrive at some idea as to how long 

 the forest has been at its work. Their fathers may also 

 tell them something about the woods in the neighborhood. 

 The following answer (from Green, p. 36) is the most 



FIG. 154. APPARATUS FOR TESTING RETENTION OF WATER BY 



DIFFERENT SOILS 



The figure represents 100 grams each of gravel, sand, barren soil, loam, and leaf 

 mould, and 25 grams of leaves 



definite that I have been able to find. He says : " It has 

 been estimated that after a sandy soil in New England is 

 so exhausted that it will produce nothing but red mosses 

 it may be renewed to its pristine vigor and productive- 

 ness by the growth of trees on it for thirty years." 



Let us next see what relations soils of different kinds 

 bear to the water that falls upon them. These questions 



