518 MR. G. BENTHAM ON COMPOSITE, 
and tierra templada, at least of Central America, are decidedly 
Mexican in character ; whilst the hot moist southern provinces 
show a much greater proportion of Columbian races and woukl 
therefore fall into the Andine region ; the transition, however, 
from the one to the other is here evidently gradual and com- 
plieated. 
It is possible, when better known, that this region may be sub- 
divided into two or more, for there are many genera peculiar either 
to the northern or to the southern districts; but at present the 
whole appear to maintain the same general character. The more 
distinet of the monotypie genera are often confined to limited 
areas as well in the north as in the south, aud those which con- 
tain several species either range over the whole area, or the 
northern and southern species blend very much together ; and in 
the superficial sketch which alone I am able now to give I feel 
compeiled to regard the whole as a single region. 
The first peculiarity that strikes one in glancing down the 
Mexican columns of the above lists is the great diversity of forms 
showu by the large number of genera, both absolute and in pro- 
portion to the species, as compared with most other regions. 
Those of the Mexican region are about 100 more than in either 
of the other three most varied regions (216 against 143 in the 
Andine, 145 in the Mediterranean, and 149 in the South-African 
regions). Nearly half of these Mexican genera are endemic, with 
an average of about threespecies to a genus, and one half of these are 
quite mono! y pic—several of them with but few eonnexions,although 
not so many perhaps absolutely isolated as in some of the Old- 
World or insular regions. If we deduct the larger genera which 
have their chief seat without the region, Vernonia, Eupatorium, 
Aster, Senecio, and Cnicus, the average number of species in the 
whole region is about four to the genus, and even with the addi- 
tion of the above five it is not much above five to the genus; whilst 
in the adjoining United-States and Andine regions it is above six, 
and in the Old World, in the corresponding Mediterranean region, 
the average is more than thirteen species to a genus. The larger 
genera of a specially Mexican type which have flourished and 
established a large number of species and varieties are Stevia, 
also abundant in the Andes, Brickellia, scarcely extending beyond 
the regiou except in a single tropical species, the homochromous 
Asteroidex, some of them repeated in the south, and the Madies 
and Tagetinez, almost endemic. 
