1906] SHANTZ—VEGETATION OF THE MESA 31 
the society. Among the- more prominent secondary species are 
Tetraneuris glabriuscula, Oreocarya thyrsiflora, Hymenopappus 
cinereus, Meriolix serrulata, Pentstemon angustifolius, Trades- 
cantia scopulorum, and Lithospermum linearis. 
Pentstemon secundiflorus society.—No species of this aspect is 
more dominant than is P. secundiflorus. On the crests of the east 
and north sides of the Mesa it forms an extensive society. Les- 
querella montana, Echinocereus viridiflorus, and Evolvulus pilosus 
are secondary species. 
Astragalus bisulcatus society.—In the clay on the south, east, 
and west sides of the Mesa, large clumps of this species are very 
conspicuous at this time of the year. Its maximum development 
is at the bottom or near the bottom of the hillsides. It usually 
occurs alone, but we may also find it associated with Sophora sericea, 
Quincula lobata, Lappula occidentalis, Allium reticulatum, Mal- 
vasirum coccineum, and Euphorbia glyptosperma. 
Astragalus Drummondii society.—This is an especially promi- 
nent society on north and west slopes, occupying about the same 
relative position as the A. bisulcatus society, but more extensive. 
Sophora sericea society.—Although badly affected with Uroymces 
hyalinus, this species becomes the dominant plant in the clay draws 
of the south Mesa. The chief secondary species associated with 
it are Lappula occidentalis, Allium reticulatum, Malvastrum cocci- 
neum, and Quincula lobata. 
Communities. 
Among the secondary species are found a number which form 
communities. These are generally of limited extent, but are of 
species which are widely scattered throughout the formation. The 
following are the more important communities: Tetraneuris glab- 
_riuscula, on crests; Lappula occidentalis, in semiruderal situations; 
Erigeron flageolaris, at the base of north and west slopes, or on the 
north and west sides of clumps of oak which have entered from the 
foothill thicket formation; E. glandulosus, on north crests; Carex 
filijolia, on portions of the north Mesa and west slopes; Quincula 
lobata, in clay; Opuntia polyacantha, either in clay, or on the gravel 
crests; Leucolene ericoides, on south crests and slopes and other 
