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VI PREFACE. 
more immediate requirements, it seems desirable to prepare a pre- 
liminary series of grass floras which, though lacking in completeness 
and not elaborated wholly upon a type basis, will nevertheless be of 
service to students of grasses who have not ready access to the scat- 
tered literature of the subject. The third paper of this volume, by 
A. 8. Hitchcock, Systematic Agrostologist of the United States 
Department of Agriculture, brings together in this preliminary way 
our knowledge of the grasses of Mexico. Since the paper represents 
preliminary work, it has seemed best to confine the study to speci- 
mens in the United States National Herbarium and to omit refer- 
ences to synonymy except in those cases in which the identity could 
be certainly established, or in which there was involved some change 
from current usage. The National Herbarium contains the collections 
of Dr. Edward Palmer, Dr. C. G. Pringle, Mr. E. W. Nelson, Dr. J. N. 
Rose and his assistants, and many other American collectors. There 
is also an important series of duplicates of several of the earlier 
Kuropean collectors, such as Liebmann, Galeotti, Botteri, and Bour- 
geau. During the summer and autumn of 1910 Professor Hitchcock 
made extensive collections in nearly all the States north of the 
Isthmus of Tehuantepec. The amount of Mexican material at hand 
is so large that the number of species omitted because of confining 
the study to specimens in the National Herbarium is probably not 
great. The number of species included by Professor Hitchcock in 
this paper is 615, of which 23 are described as new. 
The next paper, by Mr. Maxon, is the fifth of his series already 
mentioned on tropical American ferns and fern allies, and, like the 
preceding ones, deals mainly with smaller groups of species which 
are in need of revision. In addition, there are descriptions of new 
species in Marattia and Lycopodium, genera which have been 
treated synoptically elsewhere within recent years. The publication 
of several new species of Polypodium is preliminary to a review of 
the North American species of that genus. 
The fifth paper of the volume is by Mr. Paul C. Standley, of the 
United States National Herbarium, relating primarily to plants of 
Panama. The collections obtained during the recent biological sur- 
vey of the Canal Zone and adjacent parts of Panama furnish to the 
National Herbarium means of greatly extending the knowledge of 
the botany of that region. In working over portions of this material 
Mr. Standley finds it desirable in many instances to include in his 
study specimens from other parts of tropical America. Since these 
studies are likely to extend over several years it has seemed advis- 
able to publish the results in serial form. The present paper, with 
its revisions of genera, descriptions of miscellaneous new species, 
and corrections in nomenclature, is typical of the proposed series. 
