92 RYDBERG: PHY APHICAL NOTES 
4. Eurasian alpine plants, found in the mountains of the Old 
World, but not in the arctic regions. The principal subdivisions 
of this group are: 
(a) Alpestrian, endemic plants of the European Alps, including 
the Pyrenees and the Caucasus; 
(6) Altaic, north Asiatic alpine plants. 
5. American endemic alpine plants. The principal regions of 
these are the following: 
(a) Sierra Nevada, including the Cascade Mountains, which 
latter, however, contain an intermixture of some elements belong 
ing to the next; 
(6) Rocky Mountains, including the San Francisco Mountains 
- and the other ranges of Arizona, New Mexico and northern 
Mexico; 
(c) White Mountains. Most of the plants of this region belong 
to the arctic-alpine group, but endemic alpine plants are not 
wholly lacking, as for instance, Potentilla Robbinsiana and Sieversia@ 
Pecku. 
6. Circumpolar arctic plants, not found in the mountains. 
7. Eurasian arctic plants, which do not concern us at all. 
8. American arctic plants. 
9. Subarctic and 
10. Subalpine plants, which encroach on the arctic and alpine 
regions. 
CIRCUMPOLAR ARCTIC-ALPINE OR GLACIAL PLANTS 
These species probably had originated before or during the 
glacial epochs. In some cases the origin probably was somewhere 
in the Old World, in others in the New World. Of course, we cannot 
know, but we may surmise. The region which contains the most 
numbers of certain groups of species may probably be the place 
where this group originated (i. e. the home of the parent species) 
and where the individual species sprang from. As for instance, 
there is a group of arctic-alpine species of Potentilla with ternate 
leaves white-wooly beneath. Potentilla nivea is the most generally 
distributed species of the group; it is also the first and best known. — 
Where is the probable ancestral home of this species? The species 
is found in Europe, rather common in the Scandinavian mountains, 
