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 i)laces from the mountains of New 

 Mexico and the MogoUons 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 

 alon?; 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 isolated 

 peaks from Colorado to the Sierras, but if it ever reached far south it 

 must now be represented by the Strigalosi in that region and which 

 are natural derivatives from this group or the true Alpini, as is the 

 grouii 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 

 ujiper 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. Austinse and the Chsetodontes occupy similar regions 

 in the Columbia Basin and the Sierras, and A. Yukoncnsis in the far 

 north. 



The Debiles group seems to have been there in A. Bourgvovii 

 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 dis])ute. The 

 present isolation is simply the invasion of a hotter climate due to 

 teological or astromomical changes which kill the native vegeta- 

 tion and drive its progeny farther up the mountains along with 

 'he climate to which it is adai)ted till either the vegetation is all 

 killed by the petiks not being high enough to support a suitable 

 -"limate or the Arctic growth is confined to narrow limits near and 

 ■^t the tops. To attempt to account for these islands of Arctic vegeta- 

 ''on on the high peaks by bird and other animal distribution and 

 " "ind action is not tenable. The various modifications of the high 

 ■")eak climates caused by surrounding aridity below is shown by such 

 •species as A. Austinse and the Chaetodontes from A. agrestis, and 

 ''rom A. Bourgovii, etc. 



The Inflati seem to have been offshoots of the Debiles during 

 he forest period of the flo^r of the Gre-U Basin, a'ul were represented 

 'ty A. pauciflorus and miser. The great characteristic of this group 

 's its rapid differentation as the climate grew warmer, and its 

 almost total lack of differentation in the forest areas of the north. 



