GENERAL EBPOET. Uu 



limits of such papers, including in it descriptions generic and specific when- 

 ever they are not to be found in the popular manuals of the eastern floras. 

 The method pursued is that which seemed simplest and best adapted to 

 the end in view, and scarcely needs elucidation. To this have been added 

 in the Appendix concise synopses of most of the more recently revised genera, 

 thus bringing together a considerable amount of material that may be found 

 of use by those who have not ready access to the fuller original papers. 

 Among these synopses are revisions of a few genera, {Orthocarpus, Ahronia 

 and Allium^) which were prepared in connection with the present work. 



The collection, comprising about 19,000 specimens available for study, 

 but not all ranking as herbarium specimens, is distributed into sets, of 

 which the most complete belongs to the Herbarium of the Agricultural 

 Department at Washington. The second is due to Prof Eaton at Yale Col- 

 lege, and the remaining sets will be donated to such herbariums as may be 

 designated. 



There now remains but the pleasant duty of grateful acknowledgment 

 of favors and assistance received during the course of the work. Especially 

 to Prof Daniel C. Eaton is the fullest expression of thanks due for all the 

 facilities aiforded by his well-appointed herbarium-room, placed at my com- 

 mand from the outset of the work, for the constant use of his library and the 

 procurement of needed books of reference, and for assistance of every kind 

 rendered in innumerable instances, always most kindly and generously. By 

 him also the Composites, of the collection, comprising of one-seventh of the 

 whole, were carefully determined and the resulting paper forms one of the most 

 valuable portions of the Catalogue. Assistance in various portions of the 

 work has likewise been received from Dr. GtRAY and Dr. Torrey, in addition 

 to the free use of their herbariums whenever desired. Dr. GtEORGe Engel- 

 mann, also, of St. Louis, has made ready response to every application for 

 information and aid, and the articles of Col. Olney on the Carices, of Mr. 

 James on the Mosses, of Dr. Robbins on Potamogeton, and of Prof Tucker- 

 man on the Lichens, all prompt and thorough in whatever they have under- 

 taken, show that the most that was possible has been made by them of the 

 material that was furnished. 



SERENO WATSON. 



August 26, 1871. 

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