PLANT SUCCESSION AND RANGE MANAGEMENT. 29 
tention of the water supply in the upper layer of the soil in seasons 
of less than normal rainfall often causes somewhat serious desicca- 
tion in the lower soil layer, upon which yellow brush is largely de- 
pendent for water, and results in the death of many of these plants. 
Obviously, however, the desiccation of the lower soil layer is most 
serious immediately beneath the dense bunches of porcupine grass. 
As a result of the seed of porcupine grass finding ready lodgment 
and conditions especially favorable for germination immediately be- 
neath the expanded branches of yellow brush, dense tufts of porcu- 
pine grass, as shown in figure 9, often develop around the yellow- 
brush plants. The established yellow-brush plant is killed in a season 
or two or possibly straggles along for a few seasons. Where the 
competition is not too severe some of the branches of the yellow 
brush die and most of the branchlets on the remaining branches are 
killed, thus greatly reducing the leaf surface as well as the loss of 
water from transpiration. This reduction in the leaf surface often 
permits yellow brush to hold its place with the porcupine grass for 
a considerable time. Naturally under such conditions yellow brush 
produces few flowers and practically no viable seed, so that physio- 
logically its behavior is much the same as a plant that has been seri- 
ously weakened as a result of too frequent cropping. 
PA LAT ABILITY. 
With its large variety of palatable plants and its relatively small 
percentage of waste range, the porcupine-grass-yellow-brush conso- 
ciation probably furnishes as ideal a vegetative cover for all classes 
of grazing animals as the lands are capable of producing. Small 
mountain porcupine grass, of which the foliage is finer leaved and 
less harsh than that of the wheat grasses, is grazed with relish by all 
classes of stock throughout the foraging season. While vigorous 
growth ceases in most habitats during the first half of August, the 
herbage remains more or less green until well into September. When 
cured, the leafage of small mountain porcupine grass, like that of 
many other fine-leaved grasses, is cropped with relish by cattle and 
horses. Sheep take a fair proportion of the herbage after the plant 
has reached maturity, but the writer has never observed this class of 
stock to graze porcupine grass as closely as cattle and horses unless 
forced to subsist upon it. 
The seed heads of porcupine grass, unlike those of the wheat 
grasses and many other grass species, are not particularly sought for 
by stock, especially when the plant is approaching maturity or after 
the seeds have ripened. In the first place, the seeds are rather small 
and do not attract stock. In the second place, the basal portion of 
the seed is sharp-pointed while the apex elongates into a rather 
