CHAPTER II. 
NEW MEXICO AND ARIZONA DISTRICT. 
This district may be fairly considered as starting on the latitude of 
Fort Garland, a little north of the southern line of Colorado, and extending 
thence west to Loma,* on the headwaters of the Rio Grande. ‘True, a 
marked change in the flora appears about the headwaters of the Arkansas and 
runs east out into the western edge of the Great Plains at Pueblo, whence 
it shades off gradually more markedly into the flora of the warmer and more 
arid regions as we go toward the south. North of this the Pinon Pine sel- 
dom appears in Colorado; and about Pueblo not less than ten species of 
Cactacee appear somewhat suddenly in the flora. 
Taking, however, the southern portion of the San Luis Valley, as I 
have done, from Fort Garland to Loma would appear to be a more strictly 
natural division, because south of it the change is marked in the flora, and 
is further confirmed by a corresponding change into larger areas of almost 
desert land, and by a decided decrease in the relative quantity of humidity 
in the atmosphere, with a resulting smaller number of springs and running 
streams. Still, along the mountains, or on isolated mountain peaks, even 
almost so far south as the Mexican boundary, we find enough of character- 
istic Northern plants to suggest the inquiry as to whether the influences 
of the Glacial Period may have extended so far south, and driven these plants 
before it, as it did those of Labrador to the latitude of New Jersey and 
Pennsylvania on the Eastern coast. For example, we find among the mount- | 
ains of Southern Arizona,-Habenaria leucostachys, Habenaria dilatata, Goodyera 
Menziesii, Spiranthes Romanzoffiana, and Corallorhiza Macrei?. All of these — 
* T assign Loma as the western limit only because it was the western limit of my exploration. 
2 BOT 
