l6l] FLORA OF BOULDER, COLORADO I3 



its bayonet-like leaves and its large cluster of flowers. But 

 this aspect changes according to the season of the year, nor 

 is it uniform at any season. As various plants come into 

 bloom, so is it tinged red or purple, white or yellow ; here it 

 is an upland meadow of broom-grasses with purplish leaves; 

 there it is dark green with meadow-grasses ; yonder it is white 

 and hoar with sages. In early summer it is red, or purple, 

 or blue with loco-weeds, beard-tongues, and thistles, yellow 

 with golden asters, orange with cone-flowers and gaillardias, 

 or white with Mexican poppies. In midsummer the psoraleas 

 are numerous ; here and there are large clumps of lupines ; the 

 tall porcupine grasses abound, and sunflowers rear their heads 

 of gold. In late summer it is yellow with gumweeds of all 

 kinds, with golden-rods and rabbit-brushes, or purple with 

 blazing-stars and turkey-foot grasses. In autumn the gray 

 sages put forth their inconspicuous flowers, the late composites 

 ripen their achenes and whiten the landscape with their pappus. 

 But the chief plants of this formation are those not seen — 

 the little buffalo and mesquite grasses only a few inches high, 

 but forming the turf of these vast plains. There are no shrubs 

 proper in this flora. At most there are a few undershrubs 

 and suffrutescent plants, such as roses, yuccas, and the like. 

 It should be added that the vegetation of the moister por- 

 tions of the plains differs, especially in aspect and also some- 

 what in species, from that of the drier portions ; but while it 

 is possible to distinguish these two elements of the flora in 

 the extreme cases of moistness and dryness, yet in the greater 

 part of the area the two vegetations mingle inextricably. I 

 shall, however, arrange the plants typical of the Great Plains 

 into two classes, Humidae and Aridae, although the two 

 classes occur quite commonly together: 



