372 BOTANICAL GAZETTE [NOVEMBER 
important difference, as seen in the Front Range foothills, is that 
the juniper is very infrequently seen, the Arctostaphylos mostly 
dominating alone. 
Conditions of soil-moisture, soil-texture, position, slope, and exposure 
are varied. The creeping mats of bearberry are seen on rock, in gravelly 
shaded and sunny, and through a considerable range in altitude. The growth 
is more extensive and more frequent, however, away from the mountain-front, 
at elevations 800-1200 ft. above the lower limit of rock pine, being increasingly 
abundant from that height upward, and being perhaps more typical of montane 
than of foothills vegetation. Its most frequent habitat in the foothills is the 
rolling floor of the granitic upland, the soil of which is thin, coarse, mostly 
compacted (granite-gravel). Here the conspicuous vegetation is rock pine, 
in open array of scattered clumps and single trees. Parts of the treeless 
surface are occupied by large mats of Arctostaphylos, with admixture of Ceano- 
thus Fendleri (less of this upward); the rest of the area is bare or nearly so, with 
a few scattered herbaceous plants, mostly of primitive grassland. 
CEANOTHUS ASSOCIATION 
RosBIns (16, p. 41); WATSON (25, p. 207). 
_ Thespiny shrub, Ceanothus Fendleri, is ecologically similar to Arctostaphylos 
in many respects. It forms a low, matlike, spreading ground cover, and occurs 
to some extent in mixture with bearberry mats. It differs from the other in 
being typical of more exposed and xerophytic slopes, in being abundant at 
lower eh and more southerly in geographic distribution. M1iarp S. 
MarkLE informs the writer that the Ceanothus community is important in the 
Sandia Mountains of New Mexico, occurring frequently with the oaks and with 
Robinia neo-mexicana. Ceanothus ranges into dry fine-soiled habitats more 
frequently than Arcieslotiedes: and is closely associated with grassland, rather 
than pine forest. It is not evergreen. : 
Ceanothus shrubs occur in closely set or scattered patches, mostly in 
unstable gravelly or finer soil of detrital slopes. They have a strongly accelera- 
tive part in vegetation-development. Their numerous twigs and thorns, even 
in the leafless winter condition, catch and hold wind-blown and washed-down 
soil particles and bits of plant débris, thus stabilizing and adding to the soil, and 
accumulating humus. In one station this had even resulted in the building of 
small dunes of wind-blown dust, of about 8 inches height and 18 inches diameter. 
Seed burial is favored in these mats, as well as germination. Some of the more 
mesophytic of the foothills plants are seen growing up through the tangled 
branches; pine seedlings also germinate in the shelter of Ceanothus, which may 
thus be an important factor in reforestation. On dry, burnt slopes Ceanothus 
frequently covers a considerable proportion of surface and, with the Rhus 
cismontana shrub growth, is an important stage in succession after burns. 
