PREFACE. 



:o:- 



The original edition of this work, first published in 

 1868, was the result of studies undertaken in preparing 

 instruction in Agricultural Chemistry which the Author 

 has now been giving for three and thirty years. To- 

 gether with the companion volunae, " How Crops Feed," 

 it was intended to present concisely but fully the then 

 present state of Science regarding the Nutrition of the 

 higher Plants and the relations of the Atmosphere, 

 Water, and the Soil, to Agricultural Vegetation. Since 

 its first appearance, our knowledge of the subject treated 

 of in the present volume has largely participated in the 

 remarkable advances which have marked all branches of 

 Science during the last twenty years and it has been the 

 writers' endeavor in this revised edition to post the book 

 to date as fully as possible without greatly enlarging its 

 bulk or changing its essential character. In attempting 

 to reach this result he has been doubly embarassed, first, 

 hy the great and rapidly increasing amount of- recent 

 publications in which the materials for revision must be 

 sought, and, second, by the fact that official duties have 

 allowed very insufficient time for a careful and compre- 

 hensive study of the literature. In conclusion, it is 

 hoped that while the limits of the book make necessary 

 the omission of a multitude of interesting details, little 

 has been overlooked that is of real importance to a fair 

 presentation of the subjects discussed. 

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