406 MR. G. BENTHAM ON COMPOSITE. 
often short ; whilst in Conyza these corollas are still further reduced 
to a filiform tube, shorter than the style, toothed or truncate at 
the top, the ligula remaining undeveloped. The achenes, also, 
both in Erigeron and Conyza, are usually much smaller than in 
Aster, with the pappus much less copious, of finer setæ, usually 
but not always in a single row. 
The same great facilities enjoyed by many species of Erigeron 
for propagation and dispersion increase the difficulty of fixing the 
geographical origin of some of the sections of which it is composed. 
Euerigeron, ranging from FE. uniflorus and E. alpinus to E. acris, 
belongs to the northern hemisphere, and is chiefly mountainous, 
passing into the section Alpigenia of Aster, and may be as much, 
or nearly as much, of Old-World as of American extraction. 
Cenotus, the section which passes into Conyza, is now pretty 
nearly cosmopolitan, and, like Conyza, overruns tropical as well 
as temperate regions, the preponderance of local species being 
African as well as American. The other sections appear to be 
chiefly or entirely American, and perhaps all of American origin. 
Phenactis, however, belonging to the northern hemisphere, has 
two genuine Asiatic species. Phalacroloma consists of American 
annuals, two of which have overrun a great part of the Old World 
as weeds, like the. well-known Æ. canadensis, which is almost inter- 
mediate between Cenotus and Euerigeron. | .Erigeridium is a single 
N.-American species of Euerigeron, somewhat aberrant in the form 
of the achene, a deviation which does not appear to go further in 
any genera of the Erigeron group. The South-American sections 
are rather more distinct and local. Leptostelma is a purely Bra- 
zilian form, resembling some of the large-flowered North-American 
species of Plenactis, but with an exceptionally fimbrilliferous 
receptacle. This also does not connect itself with neighbouring 
genera. Oritrophium, from the Andes, aberrant both from Aster 
and Erigeron in the form of the style-branches, in other respects 
approaches the Andine section Voticastrum of Aster nearly as much 
as the northern Euerigeron approaches Alpigenia; Oritrophium 
assumes also often the habit of the more southern Celmisia, but 
differs in the achene and other characters. Terranea (E. fruticosus, 
DC.), from the island of Juan Fernandez, approaches Aster in a 
third direction, being closely connected in many respects with the 
South-American chiefly maritime Oxytripolia. 
Around Erigeron may be grouped the following slightly dum 
gent genera, designated as much by their geographical areas as by 
