Preface. ix 



sciences is ever studied with any satisfaction to the learner, it 

 must be accomplished by severe and unflinching mental effort. 

 It is hoped, however, that the language is sufficiently clear to be 

 readily appreciated by those who are really interested in the 

 subject. That all technical terms may be understood, a copious 

 glossary has been prepared in connection with the index. 



■The illustrations are largely from drawings by the writer. A 

 few have been copied from other authors, as is in each case ac- 

 knowledged. The valuable frontispiece was secured through the 

 kindness of Dr. James D. Dana, from his " Manual of Geology.'' 



The writer would here take occasion to express his gratitude 

 to very many botanical correspondents and friends for material 

 aid in the preparation of this work, either in the loan of books or 

 specimens, or in valuable notes, suggestions and corrections. 

 Were it not invidious to specify, a few might be mentioned to 

 whom he feels under special obligations, L. M. U, ' 



Bloomington, III., January, 1881. 



