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 

 Cactacece 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 leucostacliys, Hdbenaria dilatata, Goodyera 

 Menziesii, Spiranthes Romanzoffiana, and Corallorhiza Macrcaif. All of these 



* I assign Loma as the western limit only because it was the western limit of my exploration. 

 2 BOT 17 



