Feb. x 6 , 1914 
Indicator Significance of Vegetation 
4°3 
Adaptations to the Physical Conditions 
The two dominant species have somewhat different soil requirements, 
and the land occupied by this association offers a combination of con¬ 
ditions which permits them to grow side by side. Greasewood prefers 
an ample and permanent supply of moisture within reach of its roots, 
and its strong, deeply penetrating taproot (fig. 10) enables it to reach 
moisture in places where the surface soil is dry and the ground-water table 
is at a considerable depth. This plant can live in soil which is moist to 
the surface, although under such conditions the plants are never as 
large and vigorous as where a higher elevation and a subsoil of light 
texture afford better drainage. Shadscale, on the other hand, does not 
thrive with its roots in wet soil, and its presence is usually a reliable 
indication that at least the surface foot is dry during the greater part of 
the summer. 
Greasewood {Sarcobatus vermiculatus) grows in a greater variety of 
habitats than any other flowering plant of the Tooele Valley. It was 
found in one place or another in company with the dominant species 
of all of the leading associations. In much the greater part of its range 
in the valley greasewood is associated with shadscale, but there are excep¬ 
tions to this rule. The largest and thriftiest looking greasewood plants 1 
grew on the summits of dunes of pure sand, together with sagebrush, 
juniper, Eriocoma, Abronia, Eriogonum, Psoralea, and other character¬ 
istic plants of the sand-hill mixed association. Shadscale is absent from 
this community. At the other extreme greasewood occurs in company 
with Allenrolfea in land which is too wet and saline for the growth of 
shadscale. The widely different conditions in these two environments 
are indicated by the data in Table XIII. 
Table XIII .—Moisture equivalent and salt content of the soil where Sarcobatus 
vermiculatus occurred—on the sand hills and with Allenrolfea . 1 
Depth 
(feet). 
Moisture equivalent. 
Salt content. 
On sand 
hills. 
with 
Allenrolfea. 
On sand 
hills. 
with 
Allenrolfea. 
1 
6. 2 
31.0 
0.09 
2.16 
2 
6.8 
37-3 
.08 
2.08 
3 
6. 1 
27. 7 
. 14 
1. 76 
4 
7.0 
25 - 9 
. 16 
1. 25 
1 All data in percentages of the dry weight of the soil. 
The growth of greasewood on the sand hills makes it evident that this 
plant is not an infallible alkali indicator, although in the great majority of 
cases its occurrence is associated with an excess of salts in the soil, and in 
its ability to endure the presence of alkali it is surpassed by few other 
!The individual alongside the boring made in the sand hills (see Table XIII) was 6 feet high, iofeet 
across, and had several stems which were from i to 2 inches in diameter at the surface of the ground. 
