HISTORY AND GEOGRAPHICAL DISTRIBUTION. 393 
ings in the following detailed notes, that these regions are founded 
solely on the distribution of Composite, and would require much 
modification as to those orders of plants especially which take a 
part in forest vegetation. I must also explain that the Mexican 
region, here often referred to, includes California, W. Texas, 
and a portion of Central America, and that the Mediterranean 
region, in the Composite sense, must include the Levant and 
Persia. 
A. DISTRIBUTION OF THE TRIBES AND PRINCIPAL GENERA. 
1. Vernoniacee. 
This tribe, as limited for systematic purposes, consists princi- 
pally of one large genus with a number of smaller ones closely 
connected with it, forming altogether one subtribual or generic 
group of a higher order; and to this are added afew small genera 
so distinct as to leave some doubts as to their real affinities. I 
shall here, therefore, commence with the principal genus. 
Vernonia, a genus, as we now propose to limit it, of nearly 400 
species, and closely connected with about 25 smaller genera com- 
prising above 120 more species, has its chief centres in tropical 
America and tropical Africa, forming in both countries more or 
less divergent groups, but in different directions, the species more 
numerous in America, the forms more varied in Africa. From 
tropical America it spreads more sparingly into North America 
and extratropical South America, and from tropical into Southern 
Africa, and eastward into tropical and subtropical Asia, forming 
in each of these outlying districts more or less local groups. More 
than three fourths of the genus belong to the section Lepidaploa, 
which, rather from its wide geographical range and connexions 
than from its happening to include the species first taken as the 
type, may be conjectured to be nearest to the original form. At 
least four fifths of its species are tropical American ; but it includes 
also the North-American ones, a portion of those from Africa, 
and five or six Asiatic species. In this section the achenes 
are equally 10-ribbed, with the inner sete of the pappus long 
and fine, rarely slightly dilated, the outer numerous and short, 
more frequently flattened and almost scale-like than fine. This 
great multitude of species has to be methodized and distinguished 
by foliage, general inflorescence, size, and shape of the capitula, 
and by the obtuse, acute, or aristate, appressed, or squarrose invo- 
