33 
Alpini and the cold region Homalobi. The Homalobi must have 
been represented by A. campestris and montanus, (both of which 
are alpine still in some forms), throughout as is shown by their strand- 
ed occurrence now in isolated places from the mountains of New 
Mexico and the Mogollons of Arizona to the Sierras. A. tenellus 
followed a little later along the forest area. The Alpini surely were 
there in A. andinus, Labradoricus and elegans which are similarly 
but not so widely distributed. A. aboriginum followed a little later 
along the forests, the present alpine forms seem to be derivatives 
from the lower altitude forms, though the type form belongs to the 
tundra region of the far north and is confined to it. This species 
had a wide distributon as is shown by its occurrence on jsolated 
peaks from Colorado to the Sierras, but if it ever reached far south it 
must now be represented by the Strigulosi in that region and which 
are natural derivatives from this group or the true Alpini, as is the 
group Atrati, of the central plateau region. 
‚The Hypoglottides group was represented by A. agrestis, a modi- 
fication of A. Hypoglottis of Europe, of Arctic and subalpine meadows 
as is shown by distribution similar to that of the Alpini. Ths speces 
has secured a tolerance enablng it to thrive even as low as the 
upper limit of the Lower Temperate life zone in cold meadows 
throughout the Great Plateau almost to Mexico. A. nitidus seems to 
be a later offshoot of the dry Plains of the north in Montana and 
eastward, and A. Austine and the Cheetodontes occupy similar regions 
in the Columbia Basin and the Sierras, and A. Yukonensis in the far 
north. 
The Debiles group seems to have been there in A. Bourgovii 
and polaris but the only derivatives now left at the south are A. deb- 
ilis and leptaleus which have a wide distribution but are local or 
rare in wet meadows and descending into the Middle Temperate life 
zone from central Colorado to central Utah and northwestward to the 
Columbia Basin. 
The presence of Arctic species in such widely separated regions 
as the alpine peaks of mountains from Arizona northward, separated 
by arid areas, and so remote from the present Arctic was fully ex- 
plained by the pamphlet of Gray and Hooker on their transcontinen- 
tal trip in the later seventies, also by me in 1883 in the “Origin of 
the Flora of the Great Basin,” and in Contributions No. 13, and by 
others later. The only rational explanation is the one there given 
that of migration following the close of the Ice age, and is demon- 
strated by geological history beyond the possibility of dispute. The 
present isolation is simply the invasion of a hotter climate due to 
geological or astromomical changes which kill the native vegeta- 
tion and drive its progeny farther up the mountains along with 
the climate to which it is adapted till either the vegetation is all 
killed by the peaks not being high enough to support a suitable 
climate or the Arctic growth is confined to narrow limits near and 
at the tops. To attemrt to account for these islands of Arctic vegeta- 
tion on the high peaks by bird and other animal distribution and 
wind action is not :enable. The various modifications of the high 
peak climates caused by surrounding aridity below is shown by such 
species as A. Austine and the Cheetodontes from A. agrestis, and 
from A. Bourgovii, etc. . 
The Inflati seem to have been offshoots of the Debiles during 
the forest period of the floor of the Great Basin, and were represented - 
by A. pauciflorus and miser. The great characteristic of this group 
is its rapid differentation as the climate grew warmer. and its 
. almost total lack of differentation in the forest areas of the north. 
* 
