384 
Journal of Agricultural Research 
Vol. I, No. 5 
reached by the Artemisia roots. The plants then lose many of their 
leaves and make no further growth until the following spring. 1 
The total transpiring surface is small in proportion to the size of the 
plant, especially where the physical conditions are least favorable, and 
this helps to prevent rapid exhaustion of the available soil moisture. 
The limited amount of new growth made during exceptionally dry seasons 
diminishes the dan¬ 
ger of death from 
drought. Another 
circumstance which 
serves as a protection 
from this danger is 
the thinness of the 
stand. Even on the 
sand hills, where the 
conditions are most 
favorable for their 
growth, the sage¬ 
brush plants are 
rarely crowded. In 
proportion as the 
soil-moisture condi¬ 
tions depart more 
and more from the 
optimum for this 
species, the plants 
are farther and far¬ 
ther apart. Each in¬ 
dividual (PI. XLIV, 
fig. 1) is surrounded 
by a space of ground 
which is bare during 
the greater part of 
the year, although producing a few shallow-rooted herbaceous plants in 
spring and early summer. The wide spacing of the plants is indicated in 
figure 3. 
Effects of Disturbing Factors: Successions 
During the summer and autumn large areas of sagebrush are often 
burned over. The fire consumes the dry herbaceous growth and the 
sagebrush plants are usually burned to the ground. They do not sprout 
up from the old stumps, and the result is usually the complete removal 
of the Artemisia. In the following year a mat of herbaceous vegetation, 
composed chiefly of Bromus tectorum and Erodium cicuiarium , covers the 
1 Sagebrush is therefore to be classed as a “ drought-enduring’' species. See Kearney and Shantz, op. 
dt., p. 354 , 355 - 
Fig. 5.—A small plant of sagebrush (Artemisia tridentata), showing the 
deeply penetrating taproot and good development of superficial lateral 
roots typical of this species. 
