INTRODUCTION. 
The many and striking differences presented by the specimens which 
. have been referred to Stanton hystrix (Elymus sitanion) have long been 
recognized, but no one has heretofore attempted to define or classify 
them. From the material in the herbarium of the Academy of Natural 
Seienees of Philadelphia, it is evident that Nuttall distinguished at 
least two species. These are shown in Plate I, the tiekets attached 
to the specimens being iu Nuttall's An The large amount 
of material in the National Herbarium, gathere. from numerous and 
widely separated localities by many collectors, has afforded an excellent 
opportunity for a study of the variations which with the increase of the 
eolleetion became more and more apparent, and the necessity of their 
classification more and more evident. The present paper, prepared by 
my direction, was undertaken to meet this necessity, and while the 
species here defined may require some modification after further studies 
in the field, and while some classed as species may eventually be reduced 
to varieties, the subject as presented can hardly fail to be of interest 
to the student of grasses and helpful in the close discrimination of the 
species of a critical group of plants 
Nuttall, who first described the species of this genus, referred it to 
the European Ægilops and named his plant Ægilops hystrix, His 
description was carefully drawn up and his species can be readily 
„recognized. A year later, Rafinesque? published his genus Sitanion, 
based upon a single species, which he named Sitanion elymoides. It has 
been found impossible to determine with certainty which of the species 
enumerated in the present paper was the one named by Rafinesque; it 
certainly was not, however, the grass described by Nuttall. 
Our leading authorities, Bentham and Hooker, Hackel,* and Baillon,“ 
have all reduced Sitanion to a section of Elymus. The articulate rachis, 
readily breaking up at maturity, and the usually bifid or many parted 
and awned empty glumes are well-defined characters, distinguishing 
the species from Elymus, and justifying their separation as a distinct 
1Genera North American aa 1:86. 1818. 
? Journ. Phys., 89: 103. £9. 
3 Genera Plantarum 3: 
*Die Natiirlichen be 2: part 
5 Histoire des Plantes, Monographie des 9 258. 
