THE AMERICAN BOTANIST 61 



farmer can undertsand though it is thoroughly scientific is 

 every respect and is designed to serve as a text book for uni- 

 versities and colleges. A host index renders it possible for the 

 student to readily discover the nature of a given disease in his 

 crops. The volume is published by Ginn & Co., at $3.00. 



The question of the fertility of the soil and how to main- 

 tain it is one of paramount Importance to every farmer and 

 .therefore to the rest of us who depend upon the farmer for 

 food. In recent years the theory that there is in most soils a 

 sufficiency of the chemicals needed by plants for all time, has 

 been stoutly argued and as stoutly combatted by those who be- 

 lieve that soils can be worn out and must be improved by fer- 

 tilizers. A notable contribution to the discussion is "Soil Fer- 

 tility and Permanent Agriculture" by C. G. Hopkins well 

 known for his work in soil chemistry at the Illinois Experi- 

 ment Station. Dr. Hopkins is on the side of those who advo- 

 cate the improvement of our soils by fertilizers and takes no 

 uncertain stand on the subject. In his book he goes very ex- 

 tensively into the chemistry of soils, the sources of plant food 

 and crop recjuirements, and draws his conclusion in favor of 

 fertilizers. Much space is also given to detailed accounts of 

 soil investigations in this country and abroad and the factors 

 in soil fertility are carefully analyzed. However much the 

 two schools may differ, as to the effect of fertilizers, they agree 

 in this, that good crops cannot be grown indefinitely on an}- 

 soil without them. Whether they are needed, as Dr. Hopkins 

 contends, to supply an actual lack in the soil, or whether, as 

 his opponents assert, they are useful to plants only as they en- 

 able them to neutrolize various toxic elements in the soil, is a 

 question that apparently canrot be decided at present. If 

 manures are necessary to keep the plant food in the soil at its 

 highest state, it is difficult to account for the fertility of most 

 virgin soils, while the fact that certain plants are undoubtedly 



