PREFACE. 



This paper by Dr. Edward L. Greene, Associate in Botany. United 

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

 western species of Ptelea. He finds that this genus instead of being- 

 composed of only a few species is a very Large 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 ('apt. John Donnell Smith"-, eventually to 

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

 that of the California Academy of Sciences. 



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

 wise indicated are to be understood as belonging here. 



J. N. Rose, 



Associatt Curaio?'. 



