316 ELEMENTARY STUDIES IN BOTANY 



materials are found in all soils upon which natural vegetation 

 can grow. Soil is a variable mixture, and there is no fixed 

 standard that determines the best mixture. In the second 

 place, the immediate need of any soil is to be put in proper 

 physical condition, and what is necessary to accomplish this 

 can be told only by an examination of the area ; it certainly 

 cannot be told from a sample. 



