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PREFACE. 



This paper by Dr. Edward L. Greene, Associate in Botan}-, United 

 States National Mnseuin, is the result of an exhaustive study of the 

 western species of Ptelea. He finds that tliis genus instead of being 

 composed of only a few species is a very largo one, and describes 59 

 species, of which 55 are new. His work is based chiefly on the large 

 series of specimens in the National Herbarium, in his own collection 

 now deposited here, and in Capt. John Donnell Smith's, eventually to 

 come here, together with the collections of the late C. C. Parry and 

 that of the California Acadenij^ of Sciences. 



The types are chiefly in the National Herbarium, and unless other- 

 wise indicated are to be understood as belonging here. 



J. N. Rose, 



Associate Curato7\ 



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