6 DISTRIBUTION AND MOVEMENTS OF DESERT PLANTS. 
The plants of the hill and the slopes adjacent are essentially xerophytic, 
including cacti, the creosote-bush, the ocotillo, and other conspicuous and 
well-known desert forms. Many of the plants of the valley just below, 
on the other hand, are distinctively mesophytic. Such are the willows 
and cottonwoods of the river banks, the ash and elder near irrigating 
ditches, and various introduced species. Even on the hill there are some 
species growing in shady places that neither in habit nor structure show 
any special adaptation to desert conditions. Thus within the area selected 
for study there are great differences of biological types. 
With the exception of the trees already named and a very few addi- 
tional ones, the woody plants are mostly shrubs, and these exhibit great 
differences of stature and habit. Many of these are low, as if stunted, 
but a few, such as Fouquterta, for example, make a vigorous growth, as 
if growing under ideal conditions, and become thereby conspicuous fea- 
tures of the landscape. Collectively they exhibit in perfection the well- 
known characters of desert shrubs, some with greatly reduced leaves, 
others with spines, thickened epidermis, hairy coverings, fleshy reservoirs 
of water, and still other familiar devices by which protection against 
animals and against excessive transpiration has been secured. There are 
two or three climbers and a few vegetable parasites, of which Phoradendron 
and Orthocarpus are the most obtrusive, the latter, at the season of flower- 
ing, covering the hillsides with wide patches of color. 
The most striking effects, however, are produced in favorable seasons, 
when after sufficient rainfall the winter annuals appear in early spring 
-in countless multitudes, some with fine green leaves covering the ground 
like grass, others, such as the California poppy, producing masses of color 
that may be seen for miles away, and still others, less conspicuous, that 
by their rapid growth and local abundance produce a pleasing and almost 
bewildering variety where a few days before the oppressive monotony 
of brown earth and bare rocks prevailed. A similar, though hardly as 
impressive, change occurs after the summer rains, when another and 
very different set of annuals bloom and form their seeds. 
On the north faces of the rocks there are lichens of the crustaceous 
form, a few scattering mosses occur, and even a species of liverwort is 
found after the winter rains. A number of parasitic forms, chiefly of the 
Uredineze and Perisporiacee, occur on herbaceous hosts, and a very few 
species of green and blue-green alge are found in irrigating ditches and on 
moist ground; but, on the whole, cryptogamic plants constitute an incon- 
spicuous and relatively unimportant part of the vegetation and the flora. 
Grasses are fairly well represented, and although here, as elsewhere in 
tropical and subtropical regions, they grow in tufts and form no true 
sod, yet some of them, such as Hilaria, so far approach this as to form 
collectively broad patches visible at a distance, and become successful 
competitors for areas that, but for their presence, would be occupied by 
other plants. 
