32 BULLETIN 791, U. S. DEPARTMENT OF AGRICULTURE. 
plants make up the ground cover in somewhat equal proportions. 
The highest development of the porcupine-grass-yellow-brush cover 
is indicated by a scattered stand of wheat grasses, a rather conspicu- 
ous presence of blue grasses (Poa) , and a somewhat smaller amount 
of fescue grasses. The lower development of the type in question is 
characteristically indicated by the conspicuous presence of brome 
grass, and not uncommonly of fescue grasses, with the addition of 
several perennial nongrasslike plants, among which blue foxglove, 
sweet sage, and yarrow are the most common. 
So long as porcupine grass and yellow brush, including the typical 
associated species, hold their place in competition with plants of 
lower successional stages, or yield to the invasion of plants higher 
in the cycle of succession, like the wheat grasses, it is perfectly clear 
that the range is not being misused. If, on the other hand, the por- 
cupine-grass-yellow-brush consociation is being replaced by brome 
grasses, fescues, and more especially by blue foxglove, sweet sage, 
yarrow, and other plants of the second weed stage, there is indis- 
putable evidence of the deterioration of the range. 
In view of the large variety of palatable plants associated with the 
porcupine-grass-yellow-brush cover, the highest possible development 
of this type is probably the most desirable of any for the grazing of 
all classes of stock. Since the forage crop is composed both of 
weeds and grasses, with the latter distinctly predominating on the 
better developed types, the highest grazing efficiency is obtained 
through " common use," that is, through the combined grazing of 
cattle, horses, and sheep. 
THE FOXGLOVE-SWEET-SAGE-YARROW CONSOCIATION. 
Detailed quadrat data and extensive observations have shown that 
when conditions unfavorable to growth are sufficiently prolonged 
gradually to destroy the porcupine-grass-yellow-brush cover, but not 
such as seriously to change the condition of the soil, shallow- 
rooted perennial weeds of the second weed stage, notably blue fox- 
glove (Pentstemon procerus), sweet sage (Artemisia discolor), and 
yarrow (Achillea lanulosa) are the natural successors. On the other 
hand, where the porcupine-grass-yellow-brush cover is suddenly de- 
stroyed and considerable portions of the upper soil layer carried 
away, as often takes place where live stock are injudiciously handled, 
the immediate successional cover consists chiefly of annual plants 
characteristic of the first or early weed stage, with or without an 
admixture of perennial species. 
In the gradual elimination of the porcupine-grass-yellow-brush 
cover perennial weed species usually gain a foothold shortly after 
the ground is exposed or when the roots of the grass and brush cover 
