PREFACE 



1%JOW and then, out of those explorations 

 which scientific men of the severer type 

 make into the realm of the unknown, there 

 may come something of direct practical aid to 

 the race, something that makes the world move 

 a little more easily in its grooves ; though very 

 many of the discoveries are of scientific value 

 alone, of interest chiefly to isolated circles 

 of great specialists. 



There is another class of scientists, not large 

 but steadily growing, whose work in the vari- 

 ous bureaus of the Department of Agriculture 

 in Washington, and, preeminently on the staffs 

 of the Experiment Stations of the United 

 States, is not only admirably scientific in char- 

 acter and scope, but of commanding economic 

 importance. In the preparation of this volume, 

 the writer has been under obligation to this 



