16 t FLORA OF THE YELLOWSTONE NATIONAL PARK. 



We also find Elatine triandra, Schkuhr., and Flcerkea proser- 

 pinacoides, Willd. 



The genus Arnica is well represented in the Park, all the seven 

 species of the Rocky Mountains between New Mexico and the 

 British boundary have been found. Of Arabis, six out of eight 

 species, half of the dozen or so species of Ribes, and eight of the 

 ten species of Epilobium. All the species of the following genera 

 have been collected, Lonicera (4), Veronica (6), Habenaria (4), 

 and Luzula (4). The order Composite, which in North America 

 comprises an eighth of Phsenoganious Plants, in the limited area 

 of the Park has, as far as known, 38 genera and 108 species, or 

 about one-sixth of the whole. The ferns are meagrely repre- 

 sented by only six species, and these for the most part are rare 

 and local. 



ALPINE FLORA. 



As far as observed the alpine flora of the Park contains about 

 the same proportion of 'arctic species as that of the whole 

 Rocky Mountain region within the United States. In the 

 latter case out of about 190 species, 55 per cent, belong to the 

 arctic flora. In other words, this alpine flora, like that of 

 the whole temperate zone in the northern hemisphere, is a 

 southern extension of arctic vegetation. The appearance of 

 these arctic forms is looked for in the general refrigeration 

 which brought on the glacial period. Pushed southward by the 

 extreme cold, and then, as the climate moderated, retreating 

 northward, following the receding glaciers, they were left 

 stranded on the mountain summits, and finding a congenial 

 home, have there persisted. In the list of the alpine flora given 

 below, those which are arctic are marked thus (*). It will be 

 seen that the Rocky Mountain arctic alpine flora is pretty well 

 represented, considering the limited area under consideration, 

 with the exception of the Gentians, which are entirely wanting 

 as far as observed. 



Ranunculus nivalis, L., var. Eschscholtzii, Watson. 

 *Draba alpina, L. 

 Draba crassifolia, Graham. 

 Draba aurea, Vahl. 



