Origin and Development of the Composites. 21 
tion in the Mexican region, but the Aniline and Brazilian regions 
show others almost equally well developed. There is a tropical 
connection by Mikania scandens and also by Ageratum conyzoides. 
In addition there is some indication both in its present and its 
Pliocene distribution of the use of the Alaska-Siberian bridge 
by Eupatorium. 
The Piqueriinae are best developed in Mexico and the Andes, 
the Adenostylinae in Mexico and the U.S.A. regions. The main 
sub-tribe, Ageratinae, have the distribution of the Eupatorium- 
Mikania plexus, extending more or less into all the regions of 
the world. 
Helianthece. The Verhesininas have been suggested as the 
primitive sub-tribe (Pig. 7), and Spilanthes, with type 4 stamens, 
type IV style, setiferous aristae in the pappus and a sub-biseriate 
involucre seems a probable primitive genus. The distribution of 
this genus is, therefore, given (Fig. 39) together with the centres 
of the sub-tribes. 
The detailed distribution of this tribe is somewhat complex, 
as there are several more of less cosmopolitan genera, but the 
Spilanthes type of distribution is common among these wide¬ 
spread genera ; Atnbrosia, Xanthium , Siegesbeckia and Eclipta are 
examples, the last two belonging to the same sub-tribe as Spil¬ 
anthes. A northern connection via the Alaska-Siberian bridge in 
addition to the usual tropical one is indicated in Bidens. 
All the sub-tribes, except the peculiar Petrobiinas, have a 
Mexican concentration. The Verbesininas and Coreopsidinae extend 
into all the regions of the world. The Lagasceinae, Madiinae and 
Zinniinae have only a slight extension from Mexico, and the other 
sub-tribes are practically confined to America, extending more or 
less strongly into the Aniline and Brazilian regions. 
Heleniece. All the sub-tribes of the Helenieae are practically 
confined to America, and Porophyllum (Pig. 40) is taken as one of 
the widespread genera, although it is probably not the most 
primitive, faumea, Flaveria and Cadiscus are the only genera 
which extend to the Old World, but there is only one species of 
each outside America. The distribution of the Tagetinae is very 
closely similar to that of the Galinsoginae, both sub-tribes developing 
in the same regions and almost to the same degree. There is a 
distinct extension to the Chilian region in the Baeriinae and the 
Heleniinae, but only one or two species of the Jaumeina; and 
plaveriinae extend to that region. 
