40 T. Holm — Studies in the Cyperacece. 



II. Southern Species. 



e. Species common to both loorlds. 



Cfoetida^ stenop)hylla^ pyrenaica and inelanocephala. 



f. Species endemic to North America. 



C. occidentalism straminiformis^ chalciolepia, hella, scopulorum^ 

 chimaphila, rhomhoidea, elynoides^ oreocharis^Engehyianniim 

 monile and lupulina. 



When comparing the geographical distribution of these 

 Carices, the arctic-alpine are of a special interest, because they 

 prove that there are species common to these mountain-peaks 

 and to the polar regions, a fact that may point towards the place 

 where these species originated, or let us say " develoj)ed." 



And the most natural explanation seems to be, that they are 

 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 distribution would, thus, be 

 the arctic region. This explanation might be plausible in 

 respect to the circumpolar species, but less so concerning the 

 others. For in regard to the latter there is some, and indeed 

 no small, possibility for supposing that these had originally 

 developed in the South, but that they accompanied their arctic 

 brethren on their return to the JS'orth. The latter explanation 

 might be applicable especially to such species which 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 information about the center of development of such 

 species which are arctic, but not alpine, some other data may 

 be taken into consideration. We suggest the association with 

 allied species as perhaps giving some clue to the solution of 

 this problem."^ Would it not be natural to suppose that where 

 some species is found associated with a group of types which 

 appear to be closely allied to this, that '' there " may be sought 

 the center of its distribution, if not of its development? We 

 might illustrate this suggestion by an example, taken from 

 Carexf estiva. This species is arctic, but neither circumpolar 

 or strictly alpine; it is relatively rare in the polar-regions and 

 occurs there only as what may be termed the "typical" plant. 

 But much farther South and especially in the subalpine zone 

 of the Rocky Mountains is a herd of this same species, accom- 

 panied by several aberrant forms, besides by species that ai'e 

 apparently distinct, but among its closest allies : C. athrostachya^ 

 petasata^ pratensis, etc. Judging from our present knowledge 



■^Compare E, v. Wettstein : GiTindziige d. geogr.-morphol. Methode d. 

 Pflanzensystematik, 1898, p. 35, etc. 



