XVIII INTEODTJCTORY. 



Prof. D. C. Eaton, of Yale College, has written a most valuable report 

 on the Ferns. This paper differs from the others inasmuch as it is a com- 

 plete monograph of all the known Ferns of North America south of the 

 40th parallel and west of the 105th meridian, whether collected by your 

 Expedition or not. It must remain for years the standard authority on 

 the Ferns of that wide area. 



Mr. Thomas P. James, a well-known authority on the American 

 Mosses, has kindly prepared the account of these plants ; and Prof. Edward 

 Tuckerman, of Amherst College, equally well known in his own special 

 branch, names the Lichens. 



The remainder of the text I am responsible for, and though I can 

 hardly hope it will equal the portions contributed by the gentlemen above 

 named, I trust it may be of some value. I have freely quoted from other 

 authors, and have endeavored to give due credit to the sources whence any 

 information has been derived. I have cited the Genera Plantarum by 

 Bentham and Hooker as the authority for the generic descriptions given 

 throughout the Report in the form of footnotes. Though I have in the 

 main simply translated their descriptions, I have occasionally made some 

 changes to suit the particular species I was concerned with. My reason 

 for adhering so closely to these authors as I did was, that the descriptions 

 might be full enough to include other species found in the same region. 



It is a great regret to me that the material collected by Dr. W. J. 

 Hoffman, formerly of your Survey, has not been directly available. I have 

 hence been obliged to omit mention of him as the collector of many inter- 

 esting species from Arizona and Nevada. I take, however, this means of 

 recognizing the value of his work. I have elsewhere alluded to his report 

 on the "Distribution of Vegetation in Portions of Arizona and Nevada," 

 published in the American Naturalist for June, 1877. 



Almost the entire botanical collection of 1873 was made by Mr. John 

 Wolf, and it was among the largest and finest ever obtained by a Govern- 

 ment expedition. 



I was materially assisted, in 1874, by Messrs. Henshaw and Rutter in 

 the work of collecting, and in 1875, by Dr. H. C. Yarrow and Messrs. 

 Henshaw and Shoemaker. 



