REGIONS AND AREAS OF DISTRIBUTION. 527 
and for the development and differentiation of numerous species 
in a considerable number of genera. 
Among the characteristic tribes Mutisiacee evidently come 
first. This is the sole region in which they are dominant, and so 
much so as to form nearly one third of the total number of its 
Composite, and to include nearly one half of the whole number 
of American species of the tribe, fifteen of the twenty-seven 
genera of the region being almost or quite absolutely endemic. 
Asteroide:, especially the homochromous genera corresponding to 
the Mexican ones, besides Baccharis and Erigeron, the Gnaphalioid 
Inuloidew and Eupatoriacew are fairly represented; the more 
tropical or northern Helianthoidew and Vernoniace: are but very 
few; Helenioidee are also few, but more in proportion than in the 
tropical regions. The European Cichoriacee and Anthemidex 
also reappear ; and even Cynaroidee and Calendulaces are amongst 
the evidently ancient inhabitants, the former represented by five 
endemic species of the specially Mediterranean genus Centaurea, 
the latter by an endemic monotype of an otherwise African and 
Mediterranean tribe. 
7. Connexions between distant American Regions. 
Under this head we can only refer to north and south; for 
although there is a great difference between the Composite of the 
east and west coasts,both in North and in South A merica, the regions 
are continuous; there is no special eastern centre or area of pre- 
servation separated by a broad interval from the great western 
ridge, which might render the appearance of the same genera in 
both a noteworthy circumstance. The eastern genera, except a 
few local and monotypic, either extend to the western limits of 
the region or penetrate continuously into the western region ; 
some of the western genera send a few species into or all over the 
eastern region, but do not reappear abruptly after a broad interval. 
But the case is very different with respect tonorth and south. A 
considerable number of genera and even some species are esta- 
blished in extratropical North and South America, completely 
separated by a long tropical interval. The physical or other 
cendi: ‘ons which have in ancient or modern times admitted of the 
gradual extension of certain Composite races from east to west or 
from west to east have not been interrupted by the interposition of 
impassable barriers; whilst any such continuity between north 
and south is in the present geological period absolutely broken by 
LINN. JOUBN.— BOTANY, VOL. XIII, 2 P 
