Academy of Sciences.] 

 No. 3.] 



CENTERS OF DISTRIBUTION. 



35 



Til. Northern Types, Endemic to North America. 

 C. pelasata, C. Bonplandii, and C. nigricans. 

 IV. Southern Species. 



SPECIES COMMON TO BOTH WORLDS. 



C. pyrenaica, and C. mclanocephala. 



SPECIES ENDEMIC TO NORTH AMERICA. 



C. chalciolepis, C. scopulorum, C. chimaphila, and C. 

 elynoides. 



I. Northern Types. 



CIRCUMPOLAR TYPES. 



C. rigida and C. misandra. 



ARCTIC, BUT NOT CIRCUMPOLAR. 



C. nardina, C. /estiva, C. alpina, C. atrata, and C. 

 capillaris. 



II. Northern, but Not Arctic Types. 



C. siccata. 



Of these, the Arctic-Alpine species represent undoubtedly remnants of a glacial flora 

 which were left on these mountains, while the others migrated back to their northern homes 

 when the ice receded. Their center of development and distribution would thus be the Arctic 

 region. This explanation might be plausible concerning the circumpolar species, but some 

 of the merely Arctic-Alpine might have originated in the south and accompanied their Arctic 

 brethren on their return to the north. The latter explanation might be applicable especially 

 to such species as are not strictly Alpine but which nevertheless are known to occur in the 

 Arctic region. When thus the geographical distribution fails to give us any exact informa- 

 tion about the center of development of such Arctic species, which are not always Alpine, 

 some other data may be taken into consideration. As touched upon in the introduction to 

 this chapter, the association with allied species may give some clue to the solution of this 

 problem. 41 



Carex atrata may thus have developed from one center in the Rocky Mountains, a second 

 in the European Alps, and a third one in the Himalayas. A like distribution and association 

 with allied types may be recorded from several of the other species, the Alpine as well as the 

 Arctic-Alpine. Let us examine Carex /estiva , for instance. This species is Arctic, but neither 

 circumpolar nor strictly Alpine. Only the typical plant occurs in the Arctic region, where it is 

 relatively rare; but much farther south, and especially in the subalpine zone of the Rocky 

 Mountains, is a herd of this same species together with several aberrant forms associated with 

 species that are closely related to C. festiva: C. athrostachya, C. pratensis, C. petasata cet. It 

 seems, therefore, natural to suppose that C. festiva has its center of development and geographical 

 distribution in the Rocky Mountains, where it is typically developed, accompanied by allies, 

 and where it is most abundant. Its occurrence in the Arctic region may be explained in this 

 manner, that individuals of this species were among those that migrated northward with the 

 Arctic plants. But C. rigida and C. misandra may have originated within the Arctic 

 region, where they have their widest distribution and where they show, especially the former, 

 a much more pronounced tendency to develop varieties than they do farther south. A northern 

 and Arctic center may be attributed also to C. nardina. But concerning the other members 

 of the category, "Arctic, but not circumpolar types," these developed evidently in stations 

 south of the Arctic region. The third and fourth category of northern types emphasize such 

 species as are not Arctic. With the exception of C. siccata, these species are endemic to 

 .North America, where they evidently originated. Among the southern types C. pyrenaica 

 shows a remarkably wide distribution — from Colorado to Canada, Alaska, the Pyrenees, Alps 

 of Switzerland, Caucasus, Japan, and New Zealand — while its nearest ally, C. nigricans, is 

 confined to the Rocky Mountains and Alaska. Thus it seems impossible to locate the geo- 

 graphical center of C. pyrenaica, especially on account of its occurrence in New Zealand. 

 But the species endemic to this continent, naturally developed there and undoubtedly in the 

 mountains. In other words, the presence of these various types of Carex indicate that the 

 Rocky Mountains harbor a certain element of that flora, which we call the Arctic, which 

 was reared in the polar regions but forced south during the glacial epoch. The genus Carex 

 thus offers an excellent illustration of these data and in a much greater scale than most of 

 the other genera which have been discussed in the preceding pages from this same point of 

 view — geographical distribution and center of development. 



o Compare, R. V.: Wettstein: Grundzuge d. geogr.— morphol Methode d. Pflanzensystematik. 1S9S. P. 35, etc. 



