CONDITIONS FOR THE GROWTH OF TREES. 45 



In any section of country where the rainfall is 

 limited to certain periods of the year, only those 

 plants can continue to grow that, during the time 

 the rain continues and water is supplied to them, 

 or during the time the plant is actually growing, 

 can reach their maturity and develop their seeds, 

 and thus supply new germs that shall be ready 

 for the appearance of the next rainy season. 



For the growth of forests, both a certain depth 

 of soil and, in general, a certain character of soil 

 are necessary. This soil was slowly formed by the 

 decomposition of the hard, igneous rocks that origi- 

 nally formed the entire crust of the earth, and 

 contains a quantity of vegetable mould or humua 

 derived from many successive generations of plant. 



In the beginning, when the rocks' bare surfaces 

 emerged from the universal oceans, forests could 

 not grow even where the proper conditions of 

 light, heat, and moisture were present, until such 

 soil had been prepared for them. 



Extensive forests can exist naturally only in 

 regions where suitable soil exists and where the 

 rainfall during the time of growth is maintained 

 with a certain approach towards regularity, so 

 that the trees are then properly and continually 

 supplied with liquid nourishment. 



