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 Melananihae, Microrhynchae, ÄtJirochlaenae, Stenocarpae 

 and, partly also, the ÄeorastacJujae 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 ot 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 types 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 dement 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 foUowing 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 



