36 BOTANICAL GAZETTE [JULY 
and in consequence the principal species are less conspicuous than _ 
during the vernal period. 
Consocies. 
Consocies or areas dominated by the facies of the formation _ 
will be discussed later, and need only be mentioned here. ae 
Bouteloua oligostachya consocies.—This consocies is almost as 
extensive as is the formation, for this species is by far the most abun- af 
dant of any found in the region studied. A discussion of the con-_ 
socies is practically a discussion of the typical grama grass formation — 
and will be taken up later. The highest development of this con- 
socies is on the Mesa top, where the water content of this pericd | 
in the gravelly loam is 4-8 per cent. Ff 
Bouteloua hirsuta consocies.—This consocies occupies a more — 
xerophytic habitat, where the water content is 2. 5-4-5 per cents = 
It occurs on the crests and on the north portion of the Mesa in the 
gravelly soil. With this plant are generally associated Artemisia — 
jrigida, Atheropogon curtipendulus, Aristida longiseta, Bouteloua 
oligostachya, Gutierrezia Sarothrae, and many crest species. Condi- — 
tions here are the most xerophytic of any situation in the habitat. 
Muhlenbergia gracillima consocies.—This consocies is character 
istic of the clay flats where it reaches its best development. It is q 
hot uncommon to find places which are dominated by this species — 
almost to the exclusion of everything else. As a rule, howevel, — 
one finds here Bouteloua oligostachya, Schedonnardus paniculatus, — 
Artemisia frigida, Gutierrezia Sarothrae, Munroa squarrosa, Boebert t 
papposa, Plantago Purshii, Picradeniopsis oppositijolia, Euphorbia 
glyptosperma, Argemone intermedia, Atriplex argentea, Agropyrom 
occidentale, Malvastrum coccineum, and many other secondary 
species. The habitat is xerophytic, in clay or loam where the water 
content varies with the soil composition from 17-13 per cent.; the 
available water being from 2-3.5%" per roo of dry soil. 
Agropyron occidentale consocies.—This is not so important in 
Mesa region as it is farther east. It occurs, however, in the cla 
and here is usually associated with Muhlenbergia gracillima, Boule 
loua oligostachya, B. prostrata, and Atriplex argentea. 
