PREFACE. 



For the last twelve years it has been the duty of the 

 writer to pronounce a course of lectures annually upon 

 Agricultural Chemistry and Physiology to a class in the 

 Scientific School of Tale College. This volume is a result 

 of studies undertaken in preparing these lectures. It is 

 intended to he one of a series that shall cover the whole 

 subject of the applications of Chemical and Physiological 

 Science to Agriculture, and is ofiered to the public in the 

 hope that it will supply a deficiency that has long existed 

 in English literature. 



The progress of these branches of science during recent 

 years has been very great. Thanks to the activity of 

 numerous English, French, and especially German inves- 

 tigators, Agricultural Chemistry has ceased to be the 

 monopoly of speculative minds, and is well based on a 

 foundation of hard work ia the study of facts and first 

 principles. Yegetable Physiology has likewise made re- 

 markable advances, has disencumbered itself of many 

 useless accumulations, and has achieved much that is of 

 direct bearing on the art of cultivation. 



The author has endeavored in this work to lay out a 

 groundwork of facts sufficiently complete to reflect a true 

 and well-proportioned image of the nature and needs of 

 the plant, and to serve the student of agriculture for 

 thoroughly preparing himself to comprehend thp whole 

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