1917] VESTAL—FOOTHILLS VEGETATION 381 
shrubs, and some of the canyon forest plants, have fleshy fruits, and 
so may be distributed by birds. 
PLANTS OF FOOTHILLS MIXED SHRUB ASSOCIATION 
Ribes saxosum Rosa aro 
Ribes pumilum Rosa Fendleri 
Ribes vallicola recone alnifolia (7) 
Ribes longiflorum (J) Crataegus cerronis 
Jamesia americana (/) Crataegus coloradensis 
Holodiscus dumosus (/) Prunus americana (ch) 
Physocarpus intermedius (/) Prunus demissa (ch) 
Physocarpus monogynus (/) Robinia neo-mexicana (/) 
Bossekia deliciosa (f, ch) Rhus trilobata (ch) 
Rubus strigosus (/) Ceanothus subsericeus 
Rosa Sayi 
Amelanchier has been mentioned as being rare in the northern foothills, as 
may be said also for Holodiscus. The common shrubs of rock-crevice habitats 
are Jamesia and Ribes pumilum. The yellow-flowered Ribes longiflorum, 
unlike the others of the genus, is more frequent in deep, moist, fine-grained 
soil than in rocky or coarse soil. Rubus strigosus is more common in the upper 
foothills, and in less exposed habitats. It and the roses are smaller than most 
of the other shrubs. Prunus americana forms low dense thickets in rather 
exposed places. Robinia is southern. Rhus trilobata ranges into very xero- 
phytic habitats, and can persist and even establish itself on unstable soil of 
steep or loose slopes. Although a single species may make up the shrub vege- 
tation at any one spot, numbers of them occur together in a very large variety 
of combinations, particularly where the habitat is internally diverse. The 
shrub association, and consequently have been separated from it. 
relation of the mixed shrub association to the canyon forest has already been 
mentioned; the two grade into each other, but in the main they are quite 
Where the shrubs grow close together, a mesophytic undergrowth of 
herbs develops. Galium aparine or G. Vaillantii, Delphinium Nelsonii, and 
Viola canadensis Rydbergii are frequent species. The border of many shrub 
areas, where there is no grazing, shows tall herbs, as Lupinus, Achillea, 
Monarda, Pentstemon unilateralis, etc. Surface rocks, where present in 
grassland, may allow the scattering admixture of a shrub element, or even, 
where the soil is sufficiently moist, invasion of shrubs over the general 
area. 
