232 



Colorado, but, when the valleys of the streams are cultivated, will be- 

 come as plenty and as troublesome as upon the eastern slope. The 

 vegetation of the valleys of Southwestern Colorado was free from the 

 effects of irrigation, cultivation, and large herds of cattle and sheep, all 

 of which rapidly produce great changes. 



As before mentioned, the flora of Southern and Southwestern Colo- 

 rado above timber-line is nearly the same as the alpine floras of Cen- 

 tral and Northern Colorado. From timber-line (11,000 to 12,000 feet 

 altitude) down to 8,000 feet altitude, the eftects of latitude and longi- 

 tude are barely noticeable upon the flora. As we approach ISTew Mexico, 

 but very few plants of a more southern habitat appear, and very few of 

 those common in Northern Colorado are absent. The western slope 

 produces very few plants of a more western habitat until altitudes be- 

 low 8,000 feet have been reached. Below this altitude are found the 

 somewhat distinct floras of the different parts of Colorado. The flora 

 below 8,000 feet, north of the divide between the Platte and Arkansas 

 Elvers, is in greater part found southward in the parks and valleys 

 along the base of the mountains. It contains the greater number of 

 species of Astmgalns, thirty species growing, where, upon an equal area 

 southward and westward, not more than half a dozen can be found. 

 As we cross the divide and come into the valley of the Arkansas, a dif- 

 ference in the aspect of the vegetation is at once noticed. This is the 

 cactus-center of Colorado. Mentzelia is magnificently represented by 

 seven species. The Xyctaghiacew are nearly as well developed as in 

 /8'outhwestern Colorado, while Solanacece and Uiqjhorhiacew are much 

 better represented. Many plants of southern habitat, as Zinnia, Melam- 

 podium, Ximenesia, Tricuspis, &c., become quite conspicuous, and many 

 stragglers of the south here grow in their most northern location. San 

 Luis Valley, an elevated plain (7,000 to 9,000 feet altitude), does not 

 possess the different conditions necessary to the growth of an extensive 

 flora. The alkaline flats produce an abundance of Chenopodiacece. 



Many interesting plants undoubtedly grow along the boundaries of 

 the park and the edges of the mountains. Its southern portion on the 

 Eio Grande (altitude 7,000) has, in a very limited degree, the appear- 

 ance of a New Mexican flora. The number of the pbfeuogamous plants 

 growing in Southwestern Colorado will not equal the 900 species that 

 can be found upon any similar area upon the eastern slope. The im- 

 pressions received by any one who has noticed the flora of the eastern 

 slope, riding rapidly over Southwestern Colorado, below 8,000 feet alti- 

 tude, are, the great scarcity of all vegetation ; the comparative abun- 

 dance of rosaceous shrubs, and Artemisia tridentata ; the great number 

 of the annual species of Uriogonum ; the showy blossoms of Malvaceae; 

 the few species of Astragalus and Pentstemon. 



LIST OF PLAKTS OF COLOEADO NOT MENTIONED IN THE SYNOPSIS OF THE 

 FLORA OF COLOEADO, MISCELLANEOUS PUBLICATIONS, No. 4. 



Thanks are due to Dr. Asa Gray for descriptions of new species and 

 determinations of many plants of the collection ; to Dr. George Engel- 

 mann for his descriptions of new species and determinations of Cacia- 

 ce(c, LorantJiacea', and species of other orders ; to Mr. S. Watson for 

 determinations; to Prof. Thomas C. Porter for determinations of plants 

 from the vicinity of Caiion City; and to Prof. D. C. Eaton for herbarium 

 facilities and assistance; to Mr. Eugene A. Eau for the list of Musci 

 and Hepaticce ; and to Mr. J. H. Eedfield for much assistance. 



