PREFACE. 
In the act of Congress making appropriation for the Department of 
Agriculture for the fiscal year ending June 380, 1889, provision was 
made for botanical exploration and the collecting of plants in little- 
known districts of America. In the following year began the publi- 
cation of reports on this work, under the general title, Contributions 
from the U. S. National Herbarium. From 1890 to 1902 seven 
volumes were published, The present paper, the first to be issued 
since the transfer of the Contributions from the Department of Agri- 
culture to the United States National Museum, is a continuation of 
Dr. J. N. Rose’s researches on the flora of Mexico, the earlier parts 
of which appeared in the fifth volume of the Contributions. Dr, Rose 
began his work on Mexican plants in 1889, and, besides examining 
several collections made by others, he has himself made three journeys 
to Mexico, which have enabled him to supplement his critical herba- 
rium studies by valuable field observations, All the types and a full 
set of the other specimens on which the paper is based are deposited 
in the U. S. National Herbarium, now a part of the collections of the 
U.S. National Museum. 
Freperick VY. CoviLir, 
Curator of Botany. 
IIL 
