922 
Journal of Agricultural Research 
Vol. XXVII, No. 12 
moisture, irrigated crops may be grown. The osmotic concentration, 
specific electrical conductivity, and chlorid content of the tissue fluids 
are higher than in any of the preceding associations. The leaf-tissue fluids 
of Atriplex confertifolia may under some conditions develop an osmotic 
concentration as high as 150 atmospheres, specific electrical conductivity 
of 0.129 mho, and a chlorid content equivalent to over 100 gm. of common 
salt per liter of leaf-tissue fluids. 
The greasewood-shadscale (Sarcobatus vermiculatus and Atriplex con¬ 
fertifolia) association occupies a belt lying between the shadscale asso¬ 
ciation and the grass flats and salt flats. It also occupies the ridges 
and hummocks which diversify the highly saline mud flats along the 
southern shore of the Great Salt Lake. Soil moisture and salinity are 
much higher than in any of the preceding associations, and agricultural 
development must involve irrigation, and in some places drainage as 
well. The average osmotic concentration of the leaf sap of the woody 
species is over 30 atmospheres, the average specific electrical conduc¬ 
tivity is over 0.045 mho, and the average chlorid content over 18 gm, 
of Cl per liter. 
The grass flats occupy land of high moisture content but of highly 
variable salinity. The physicochemical constants of the tissue fluids 
are closely correlated with the salinity of the ground water. The values 
of osmotic concentration, specific electrical conductivity, and chlorid 
content are, roughly speaking, comparable with those found in the 
preceding and the following associations. Except when the conditions 
can be modified by drainage (which is generally impracticable because 
of the low level of the land), the grass flats have greater value for graz¬ 
ing or for natural hay production than for any other crop. 
The salt flats are characterized by soil of exceedingly fine texture 
which is moist for a large part of the year. In late summer salt crystal¬ 
lizes out over the surface. Plants are found only on small hummocks 
or along drainage channels from springs. AUenrolfea occidentalis and 
Salicornia utahensis , both stem succulents, are the chief species. These 
are both characterized by an osmotic concentration of about 40 atmos¬ 
pheres, a specific electrical conductivity of over 0.060 mho, and a chlorid 
content of 17 to 30 gm. per liter of tissue fluid. 
From the foregoing outline of the findings as to matters of fact, it is 
clear that there is a close parallelism between the physicochemical prop¬ 
erties of the tissue fluids of the native species on the one hand and the 
characteristics of the soil and the capacity of the land for crop produc¬ 
tion on the other. 
The fact that few agricultural plants of importance have sap proper¬ 
ties similar to those of the native desert species probably furnishes the 
explanation of the failure of crop plants in the more severe of the habi¬ 
tats of this region except as their conditions are modified by irrigation. 
LITERATURE CITED 
(1) Cavara, F. 
1905. RESULT ATI DI UNA SERIE DI RICERCHE CRIOSCOPICHE SUI VEGETALI. 
Contrib. Biol. Veg. R. 1 st. Bot. Palermo 4: 41-80, illus. 
( 2 ) CLEMENTS, F. E. 
1920. PLANT INDICATORS: The RELATION OP PLANT COMMUNITIES TO PROCESS 
and practice. 388 p., ilhis. Washington, D. C. (Carnegie Inst. 
Wash. Pub. 290). 
(3) Dixon, H. H, and Atkins, W. R. G. 
I913. OSMOTIC PRESSURES IN PLANTS. I. METHODS OF EXTRACTING SAPS 
PROM plant organs. Sci. Proc. Roy. Dublin Soc. (n. s.) 13: 422-433. 
