Flora of the Rocky Mts. and Sierra Nevada. 191 
during the glacial period but which was subsequently interrupted by later 
changes, confining the arctic-alpine species to those habitats, even if far re- 
moved from each other, which possess a soil derived from rocks of a similar 
chemic constitution. 
4. The Flora of the Rocky Mountains and of the 
Sierra Nevada. 
During that extensive glaciation of the northern hemisphere and local glaciations 
in the southern, these elevations and depressions of the snow-line on all mountain 
ranges would have been at a maximum. At the present time, the only unbroken 
chain of mountains and highlands, connecting the arctic and north temperate with 
the antarctic lands, is to be found in the American continent, the only break of 
importance being in the neighborhood of the Isthmus of Panama, where there is a 
distance of about 300 miles occupied by rugged forest clad hills, between the lofty 
peaks of Veragua and the northern extremity of the Andes in New Granada. 
We should accordingly expect that this great continuous mountain-chain has 
formed the most effective agent in aiding the southward migration of the arctic 
and north temperate vegetation, which occurred during the period, or after 
the period of maximum glaciation, when as before mentioned, suitable con- 
ditions were found on the high mountains for their spread.. We do find in 
fact, not only that a large number of northern genera and many species are 
scattered along this route, but at end of the long journey, in southern Chili 
and Fuegia they are found in numbers sufficient to form an element in the 
flora of those countries. 
The alpine regions of the Rocky Mountains support an important 
number of endemic forms of plants which are related to species of the arctic 
alpine flora and in part to species which occur in the plains below. So 
Gentiana Newberryi stands near G. glauca and G. frigida, which are found 
in. the Rocky mountains and in Siberia. Astragalus oroboides (= Phaca elegans) 
shows close affınities with Aszragalus alpinus (= Phaca astragalina), Dryas 
Drummondii to Dryas octopetala. The question naturally arises: have these 
endemic forms been evolved as new species out of arctic-alpine forms since 
their migration along the Rocky Mountains, or do they represent in part the 
relicts of a former arctic-alpine vegetation, the congeners of which have dis- 
appeared except on the mountain summits of the west? To satisfactorily 
answer these questions, the following table of the alpine dicotyledonous 
plants of the Rocky Mountains is given. 
A horizontal line (—) before the name indicates that the plant occurs also in Asia, a line (—) 
after the name that the plant occurs in Greenland and eastern North America, while a vertical 
line (1) before the name indicates that the species is-only present in the arctic regions of America, 
and with Eu., that it is present also in the European mountains, Scandinavia, Iceland. The southern 
limit of each species is given by eiting the latitude beyond which it does not apparently extend. 
The first list is based upon a manuscript list of plants n to Prof. O. DRUDE in a 
letter from Fr. BRENDEL, dated Peoria, Illinois, January 4, 1888; ENGLER, A., Entwickelungs- 
geschichte, pp. 150—151; RYDBERG, P. A., Flora of Montana ei een an Park, 1900; 
