86 MR. G. BENTHAM ON GRAMINES. 
received the name of Schmidtia. 18. Purppsrsx, Br., is a dwarf 
paniculate slender Arctic grass, ehiefly distimguishable from Spo- 
robolus by the minute lower empty glumes. 
19. SroroBoLus, Br. (Vilfa, Beauv., Agrosticula, Raddi, Tria- 
chyrium, Hochst., Cryptostachys, Steud.), is now a genus of about 
eighty species, spread over the warmer and temperate regions of 
both the New and the Old World, mostly, however, American, with 
a very few European or Asiatie. Ineluded by the older authors 
in Agrostis, it has since been universally acknowledged as dis- 
tinet, though different characters have been assigned to it. 
Beauvois, who attached primary importance to the presence or 
absence of the awn, referred to it all the unawned species of the 
old genus Agrostis. Brown, who first pointed out the differences 
in the fruit, took as the principal character the loose membra- 
nous pericarp readily detachable from the seed ; but this, though 
very conspicuous in S. indicus, Br., and in some other species, is 
not apparent in the dried state in several others; and in S. virgi- 
cus, Kunth, and others, it is only when soaked that the pericarp 
can be detached. On this account it has been attempted to 
establish two genera, Vilfa and Sporobolus ; but the character is 
far too indefinite, as well as uncertain, to be available even for 
sectional separation. As a whole, Sporobolus is chiefly distin- 
guished from Agrostis by the total absence of any dorsal awn, 
and by the grain so loosely enclosed in the glume that it usually 
protrudes from it when ripe, and often falls away. The palea 
also generally splits readily into two, and in some species is 
even at the time of flowering divided to the base, a character 
which Grisebach, who only observed it in an Argentine species, 
was induced to take as that of a new genus Diachyrium ; but it 
exists in many other species; and this divided palea has been 
more than once described, and even figured (as in T. Nees’s 
* Genera Flore Germanice ’), as a two-valved pericarp, a character 
unknown in Graminee. Brown’s name Sporobolus was rejected 
by Beauvois, Trinius, and others on the supposition that the genus 
is identical with the older established Vilfa, Adans. That, how- 
ever, is a mistake. Adanson’s character of Vilfa is so vague 
that it cannot be identified by that alone; but in his index he 
fixes it by quoting two European species, which are certainly both 
of them true species of Agrostis. 
Two North-American species of Sporobolus, S. compressus, 
Trin., and S. serotinus, A. Gr., are exceptional, not only in the 
