MR. G. BENTHAM ON GRAMINEX. 35 
pical American, a few of which are also generally spread over 
the warmer regions of the Old World, especially P. distichum, Linn. 
(P. vaginatum, 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 :— 
Gardner, n. 2354, is repeated under P. malacophyllum and 
P. subsesquiglume. S 
Hostmann, n. 658, under P. densiflorum and P. cespitosum. 
P. distachyum, Salzmann, n. 667, under Ë. pumilum and P. 
divergens. 
Gardner, n. 3496 and 3497, under P. maculosum and P. notatum. 
Gardner, n. 2975, under P. vaginatum, P. tropicum, and P. 
Jilifolium. 
P. cespitosum, Hochst., n. 1543, ) 
P. amazonicum, Trin., and EE 
P. humile, Steud., : 
Digitaria uniflora, Salzm., n. 659, | under P. platycaulon and 
“and Spruce, n. 679, P. furcatum. 
P. surinamense, Hochst., n. 1283, under P. furcatum and P. 
^ scoparium. 
Spruce, n. 30, under P. chrysodactylon and P. ehrysoblephare. 
under P. plicatulum and P. 
Fournier enumerates 40 Mexican species, of which thirteen 
are described as new ; but he is, in Grammes, generally disposed 
to admit as distinet 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 affect 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, 
