United States Engineer Office, 



Geographical Surveys West of the 



One Hundredth Meridian, 

 Washington, D. C, May 10, 1878. 



General : I have the honor to submit herewith reports that go to make 

 up Volume VI of those authorized to be published by acts of Congress 

 approved June 23, 1874, and February 15, 1875. 



The volume comprises a number of reports upon collections of the 

 years 1871 to 1876, inclusive, made by Dr J. T. Rothrock, surgeon and 

 botanist to the Expeditions of 1 873-4-5, and by eminent specialists. 



The collections obtained during the several years, after their identifica- 

 tion and classification, have been forwarded, through the Smithsonian Insti- 

 tution, for final lodgment in the herbarium of the Agricultural Department. 



The following gentlemen have been engaged as field assistants in this 

 branch, viz: Dr. W. J. Hoffman and Ferdinand Bischoff in 1871, Dr. H. 

 C. Yarrow and H. W. Henshaw in 1872, John Wolf in 1873, Dr. J. T 

 Rothrock in 1873-4-5, with Messrs. J. M. Rutter in 1874 and C Shoemaker 

 in 1875 as sub-assistants, and in 1874-5-6 Dr. Oscar Loew. 



Other members of the Expedition have also contributed to the large 

 aggregate of specimens. 



By dint of much pains and labor a number of species new to botanical 

 science have been discovered, twenty-seven of which are here figured for 

 the first time, as well as ten species rare, but not hitherto unknown. The 

 total number of new species is fifty, and two distinct genera have been 

 added to the known Flora of this portion of the United States New and 

 well-marked varieties of older species have been obtained, and among them 

 a number hitherto scantily represented in the largest herbaria. In many 



