viii PREFACE 



To encourage the teacher, let me say that much of the science 

 of agriculture can be successfully taught without a field or a gar- 

 den, and even without complete knowledge of the art. Thus, you 

 may teach why clover should be grown and when it contains the 

 most nitrogen, but leave the farmer to determine for himself when 

 to plow it under, if he is the better judge of seasonal conditions 

 and of their probable influences upon his own soil and crop. 



CYRIL G. HOPKINS 

 UNIVERSIT^ OF ILLINOIS 

 URBANA 



