PREFACE. 



The paper presented herewith is essentially a revision of Bulletin 

 No. 18 of the Division of Vegetable Physiology and Pathology of the 

 U. S. Department of Agriculture, published in 1899. The edition of 

 this bulletin has been for a long time exhausted. In the preparation 

 of this new edition considerable new material has been added and 

 modifications have been made by Dr. Loew, who is now professor of 

 agricultural chemistry in the Imperial University of Japan. It has 

 been thought best, in view of the changes, to publish this as a bul- 

 letin of the new series. 



A correct understanding of the physiological role of mineral nutri- 

 ents lies at the foundation of all work in plant nutrition. The 

 relation of nutrition to the health of plants and the quality of their 

 products is receiving more attention than formerly, and is a matter of 

 great YJi'actical and scientific importance. The purpose of this paper 

 is to present a resume of what has been accomplished up to the pres- 

 ent time b}^ the numerous investigators who have given the subject 

 attention. The matter has been prepared, as in the former work, pri- 

 marily for teachers and experiment-station workers, and it is therefore 

 treated from a technical rather than from a practical standpoint. 



Albert F. Woods, 

 Pathologist and Physiologist. 



Office of the Pathologist and Physiologist, 



Washington, D. C, May 21, 1903. 



