38 BOTANICAL GAZETTE [yuLy 
tion. It is also successful as a ruderal, but at places within the 
formation may become far more numerous than any other species. 
Communities. 
The following communities also occur: Schedonnardus panicu- 
latus, near the mountain and in clay; Atheropogon curtipendulus, 
on north slopes; Sideranthus spinulosus, on south slopes and crests; 
Atriplex argentea, in ruderal clay; Bouteloua prostrata, in clay south 
of the Mesa, also in ruderal or semiruderal habitats; Sitanion ely- 
modes, on south slopes; Muhlenbergia gracilis, on north slopes; 
Artemisia canadensis, on north and west slopes; Leucolene ericoides, 
crests and xerophytic places; Andropogon furcatus, on north Mesa 
in gravel; Andropogon scoparius, on gravel crests; Thelesperma 
gracile and Gaura coccinea continue from the previous aspect. 
Within this area there is one family of Oonopsis joliosa (Gray) 
Greene, which is about three years old and has spread to cccupy 
Tes a 
General. 
In considering the aestival aspect as a whole, much is found 
that will be discussed under the formation. Zonation during this 
aspect is shown as in the preceding aspect. The Mesa top is domi- 
nated by the typical formation—Bouteloua oligostachya consocies— 
the crests by the B. hirsuta consocies, the hillsides by the typical 
formation tending towards the B. hirsuta consocies, and the low 
lands surrounding either by the typical formation or by this alter- 
nating with the Muhlenbergia gracillima or Andropogon occidentale 
consocies. 
This zonation is largely due to differences in water content. 
The Mesa top and the slopes have nearly the same water content, 
there being about 2-3" of available water; the crests have a less 
amount, 1-2" ; while at the base, in the clay, the available water 
is from 2. 3-3,88™, 
The greater part of the Mesa top is occupied by the Bouteloua 
oligostachya consocies. Almost any of the other species noted 
under this aspect, whether they are primary or secondary, may be — 
found associated with B. oligostachya. The most noticeable forms — 
found on the Mesa at this time are B. oligostachya, Muhlenbergia 
