Holm, The genus Carex in North-West America. 25 
these are much better represented on the Atlantic than on the 
Pacific coast, yet by distinctly American types. — On the other 
hand the Melananiliae, Microrlujndiae, Athroclilaenae, Stenocarpae 
and, partly also, the Äeorastachyae are most amply represented on 
the Pacific coast. 
If the question be asked, how many old-world species are 
among these Pacific- and Atlantic-coast Carices, the answer 
will be: 60 on each coast and these are mainly the same and 
more or less northern species. 
It would thus appear as if the Vegetation of Carex on the 
Pacific and Atlantic coast represents a commingling ol species, 
most of which are strictly American types, while others are, also, 
distributed in the old world, in other words throughout the northern 
hemisphere. The concentration of so many species on this 
continent, as are known, also, from the old world, may be explained 
as a result of migration during or after the Glacial epoch, unless 
we admit, also, the possibility of several centers of development 
in Connection with the several centers of geographical distribution. 
When we consider the extremely rieh representation of certain 
greges, or at least groups of these, on the Pacific coast and the 
comparatively large number of t 5 ^pes i. e. species peculiar to these 
regions, we must admit that the genus shows here an enormous 
vitality and power to produce species of characteristic habit. The 
natural conditions of the Pacific coast seem especially favorable to 
the development of peculiar types. The extreme dryness that 
prevails in the Highland in contrast to the slope, besides the 
almost uinterrupted mountain-ranges traversing the coast from 
north to south. These same factors, and perhaps especially the 
considerable height of the mountains may be the cause, why the 
Atlantic element of American Carices is so very sparingly re¬ 
presented within our region, although many of the Atlantic species 
have found their way west to the central States, in the north as 
well as in the south. 
An immigration from the east seems thus largely impeded by 
the direction and height of these mountains, while, as will be 
shown in the following pages, immigration from the north seems 
probable and not very difficult; we remember for instance the 
presence of 13 circumpolar species and many others from the northern 
parts of the old world. To some extent our region in North¬ 
west America occupies a somewhat secluded position, and has 
hardly been influenced much by immigration from eastern Asia, 
as far as concerns ,,types“ in the stricter sense of the word. As 
a matter of fact none of the very few species which North-West 
America has in common with Eastern Asia may be looked upon 
as Asiatic rather than American types; they seem to be most 
abundant in Alaska. 
North-West America represents, no doubt, a most important 
Center of geographical distribution and of development of certain 
species ,,North-Western types“. Besides this region there are, 
however, several others in which the genus is equally well or even 
better represented. We think especially of Japan, Himalaya and 
New Zealand. Franchet has enumerated 111 species peculiar to 
