DIFFERENT ALTITUDES IN COLORADO 49 
is reduced to 139, in the higher foothills to 130, in the montane 
area to 107, and in the subalpine area to 50. It will be seen that 
there is a reduction in species roughly corresponding to increase 
of altitude. But the change from the montane dry grassland 
(at Tolland) to the subalpine dry grassland (at Bryan Mountain) 
is very abrupt. 
It is sometimes difficult to decide whether a given species is 
to be included as properly belonging to a certain grassland. The 
attempt has been to exclude stragglers and accidental members, 
in other words to keep the lists reasonably small. 
While the systematic list ,tells what particular species are 
found at the various stations it gives little idea of the true ap- 
pearance of each grassland area. At the mountain front, as 
already noted, there is a great variety of plants. The average 
height of the vegetation is taller than elsewhere; many of the 
grasses and other plants are 3-6 dm. tall, and some are taller. 
Certain species are conspicuous which either do not occur at all _ 
higher up or else are infrequent, as, for example, Agropyron spi- 
catum, the Andropogons, Bromus brizaeformis; Yucca glauca, the 
Delphiniums, the Petalostemons, Tium Drummondii, the various 
Cactaceae, the Gauras, Helianthus petiolaris, Laciniaria punctata, 
and Rattbida columnifera. 
At Tolland the number of species is still ie but a certain 
few are especially abundant and dominate wide areas, as, for 
example, the following: Mertensia Bakeri, which flowers in May; 
Aragallus Lambertii, which flowers in early July; Sedum stenope- 
talum, in mid-July; Campanula petiolata and Orthocarpus luteus, in 
August. The average height of vegetation in midsummer is 2-3 
dm. Grasses and sedges are abundant, especially where the soil 
has considerable humus. Here the dry grassland becomes what 
the writer calls the Muhlenbergia-Danthonia Consociation (of the 
Derivative Dry Grassland Association of the Montane Zone.) 
‘The dry grassland at Bryan Mountain (Carex elynoides Associ- 
ation) has a rather striking appearance because of the tufted 
masses of the dominant plant. This is, however, of low growth 
and the association does not look at all like the bunch grass asso- 
ciation of the plains. Conditions are somewhat mesophytic. on 
account of low temperature and frequent showers, so that many 
