37° BOTANICAL GAZETTE [NOVEMBER 
So many of the oaks do not reach tree size that the assemblage in many 
places presents the appearance of chaparral. As might be expected from their 
wide range of habitat-tolerance, they vary considerably in appearance, from 
shrubby scattered trees or stunted thickets, to low forest with mesophytic 
undergrowth. In very favorable stations, as along streams in the southern 
foothills, the oaks may reach a height of 20 ft. and more. The undergrowth in 
ungrazed parts of the oak scrub has a decidedly mesophytic stamp during the 
moister part of the season; Pulsatilla, Castilleja, Monarda, Calochortus, 
Lupinus, Geranium, Galium boreale, Campanula, Thermopsis, Danthonia, 
Pentstemon unilateralis, are typical of oak borders and less densely shaded parts 
within. Dense closed shaded oak scrub shows abundance of a tall white- 
flowered umbellifer, Ligusticum Porteri (?).4 Late summer shows many of the 
less xerophytic composites, including species of Aster, Solidago, Erigeron, and 
Brickellia grandiflora var. minor. The undisturbed clumps of small oak trees, 
where these alternate with dry grassland, are often bordered with tall, rather 
mesophytic herbs, as Lupinus argenteus, Monarda spp., and Achillea millefolium 
L. (A. lanulosa Nutt.), as may be seen in fig. 5, taken west of Castle Rock. 
Low scrubby oak thickets, in grazed areas, are mostly impenetrable to 
horses and cattle; they are, however, eaten from the outside, and the patches 
thus slowly reduced in area. This results in a complete replacement of oak 
by grassland, as stated by SHANTz (22, pp. 182, 203). When, however, the 
height of the small trunks in the middle of a clump becomes too great for the 
animals to reach the top leaves, their safety is assured. In these taller growths 
the lower parts of the trees are much less dense; if there is no outer border of 
dense thicket, grazing animals are enabled to enter; the assemblage is now 4 
scrubby forest of low trees, with open spaces between the trunks and very 
scanty undergrowth, as in fig. 6. Grazing animals may thus have a large part 
in determining the character and distribution of the oak vegetation. 
CERCOCARPUS ASSOCIATION 
CLEMENTS (r, p. 6) and SHANTz (22, p. 179), foothill thicket formation, in 
rt; RAMALEY (12, pp. 124-126), Cercocarpus shrub formation; 
pace (15), local distribution in a square mile of rock Siee and foothills; 
SCHNEIDER (21, p. 292), thicket of south slopes, in part. 
Ragged shrubs of Cercocarpus parvifolius, or, as it is called, 
mountain mahogany, form a characteristic vegetation in dry 
exposed rocky places, particularly along the mountain-front, on 
butte-slopes, hogback ridges, stony mesa-crests; in the foothills 
it is most abundant on south-facing side-slopes, or on the outermost 
slopes facing eastward on the plains. The stony fragments of the 
4 Either L. Porteri C. and R., or L. affine A. Nels., as determined by E. E. SHERFF. 
