68 ME. G. BENTHA.M ON GEAMUfEJB. 



by their inflorescence; the spikelets are singly scattered or 

 clustered along the inarticulate branches of the panicle or, in the 

 very few cases where they are in pairs, the two of each pair are 

 perfectly similar. Tristeginese are distinguished from Agrosteee 

 by the characters which separate the two primary series PanicacesB 

 and PoacesB. The tribual name was given by Nees from the genus 

 Melinis, which he published as Tristegis, believing it to be new ; 

 and although its identity with Beauvois's Melinis has since been 

 established, it does not seem worth while now to alter the tribual 

 name, which has been pretty generally adopted. Of the thirteen 

 following genera, several of them common to the New and the 

 Old World, the first four, with three glumes to each spikelet, are 

 temperate or subtropical, the following nine all tropical, with four 

 glumes to the spikelet. 



1. Thitebeeia is a new name I have been compelled to substitute 

 for Qreenia of Nuttall or Scleraohne of Torrey, both of which had 

 been preoccupied. The genus is limited to two North-American 

 species which Steudel has proposed to unite with Limnas; but 

 they differ essentially from it in the awn of the flowering glume 

 terminal, not dorsal, in the distinct styles, and other characters 

 besides habit. I have named the genus after G. Thurber, who has 

 much studied North- American G-ramineae and worked them up 

 for S. Watson's Californian Mora. The genus formerly dedi- 

 cated to him by Asa Gray has since proved not to be distinct from 

 Qossypium, to which it has been reunited by the author himself. 



2. Limnas is a single perfectly distinct species from East- 

 Eussian Asia, well described and figured by Trinius. 



3. PoLTPOGON, Desf., a genus readily known by its dense in- 

 florescence and the long awns of its empty glumes, is one of those 

 which interferes in some measure with general classification. It 

 has usually been placed in Agrostese ; but the very decided arti- 

 culation of the pedicel removes it from that tribe to the Triste- 

 ginese, where in many respects it is allied to Garnotia. It consists 

 of about ten species, dispersed over the temperate regions both of 

 the northern and the southern hemisphere, one of them almost 

 cosmopolitan, but they are rare within the tropics. It was first 

 published by Savi under the name of Santia in the Memoirs of the 

 Italian Society of Science, a publication which had so little circula- 

 tion that the name has not found its way into standard works, and 

 that of Desfontaines has now been so long and so generally in use 

 in all countries, that it would only create useless confusion now to 



