ME. a. BENTHAM OS GBAMINEyE. 35 



pical Americau, a few of which are also generally spread over 

 the warmer regions of the Old "World, especially P. distichwm, Linn. 

 (P. vaginatvm, Sw.), which reaches southern Europe as an intro- 

 duced weed. Scarcely five species can be regarded as belonging 

 exclusively to the Old "World. The above estimate of the total 

 number is founded chiefly on the investigations of Munro, who 

 had nearly completed the working-up of the genus, and has left 

 full descriptions with diagnoses and synonymy of 138 species, 

 besides a few that he had left for further inquiry. Steudel 

 enumerates 262 species, but nearly half of them have proved to 

 be mere synonyms or very slight varieties. Doell describes in 

 detail 105 Brazilian species ; but some of them are what I cannot 

 consider as really distinct ; and his own views of them were any 

 thing but stable, as there are several which he at one time re- 

 ferred to one species and later transferred to another, forgetting 

 to eliminate them from their former place, thus : — 



G-ardner, u. 2354, is repeated under P. malacophyllitm and 



P. subsesquiglvme. 

 Hostmann, n. 658, under P. densiflorum and P. ccsspitoswn. 

 P. distachyum, Salzmann, n. 667, under P. pumilum and P. 



divergens. 

 G-ardner, n. 3496 and 3497, under P. maculosum and P. notatum. 

 Q-ardner, n. 2975, under P. vaginatum, P. tropicum, and P. 



_filifoUum. 

 P. ccBspitosum, Hochst., n. 1543, | ^^^^^ p n^^^^i^ ^nd P. 

 P. amaxomcmn,J^m., and \ dissectim. 



P. numile, bteud., J 



Bigitaria uniflora, Salzm., n. 659, ] under P. platycaulon and 



and Spruce, n. 679, J P. furcatmn. 



P. surincmense, Hochst., n. 1283, under P. furcatmn and P. 



Spruce, n. 30, under P. chrysodactylon and P. chrysollephare. 



Tournier enumerates 40 Mexican species, of which thirteen 

 are described as new ; but he is, in G-raminese, generally disposed 

 to admit as distinct species forms which I perfectly agree with 

 Munro in regarding as slight varieties, corresponding to what so 

 many local European botanists describe as critical species. 



"With regard to the subdivision of the genus, Trinius, in his 

 several revisions, distributed the species chiefly according to the 

 size of the spikelets, which, however much it may afi'ect the 

 general aspect of the species, is in many cases far too uncertain 

 a character to be practically useful. Nees, in his ' Agrostologia 

 Brasiliensis,' proposed six sections, which Doell reduced to four, 



