PREFACE. 
The work entitled “ How Crops Grow” has been re- 
ecived with favor beyond its merits, not only in America, 
but in Europe. It has been republished in England under 
the joint Editorship of Professors Church and Dyer, of 
the Royal Agricultural College, at Cirencester, and a 
translation into German is soon to appear, at the instiga- 
tion of Professor von Liebig. 
The Author, therefore, puts forth this volume—the com- 
panion and complement to the former—with the hope that 
it also will be welcomed by those who appreciate the sci- 
entific aspects of Agriculture, and are persuaded that a 
true Theory is the surest guide to a successful Practice. 
The writer does not flatter himself that he has produced 
a popular book. He has not sought to excite the imagi- 
nation with high-wrought pictures of overflowing fertility 
as the immediate result of scientific discussion or experi- 
ment, nor has he attempted to make a show of revolution- 
izing his subject by bold or striking speculations. His 
office has been to digest the cumbrous mass of evidence, 
in which the truths of Vegetable Nutrition lie buried out 
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