Mar. 22, 1924 
Tissue Fluids of Indicator Plants 
919 
words, the principal types of vegetation, where typically developed, are 
reliable indicators of the physical conditions of the environment. ” 
In summarizing their observations on the attempts, some of them 
highly successful and others complete failures, to utilize the region 
for agricultural production, they point out that successful growth of 
crop plants, with or without irrigation, is so related to the physical and 
chemical characteristics of the soil, that within limits it can be predicted 
from the botanical composition of the native vegetation. 
Our studies, conducted with the definite purpose of supplementing 
those of our predecessors, have shown that such physicochemical proper¬ 
ties of the plant-tissue fluids as osmotic concentration, specific electrical 
conductivity, and chlorid content differ from type to type of vegetation, 
and in such a way as to parallel in a striking manner the findings of our 
predecessors in this field. 
In Tooele Valley inadequacy of soil moisture and a high salt content 
may combine in various ways to influence the appearance and botanical 
composition of the vegetation, to determine the physicochemical prop¬ 
erties of the native species of which the vegetation is made up, and to 
limit crop production. 
The salts of the soil may conceivably be detrimental to crop pro¬ 
duction in two ways: First, chemically, through the toxicity of certain 
of the constituents; second, physically, through the attainment of an 
osmotic concentration greater than that which can be tolerated by crop 
plants. The problem of toxicity falls quite outside the scope of this 
paper. 
Quantitative information concerning the concentration of the soil 
solution as it actually influences the plant in these deserts is not yet 
available, except for the most extreme conditions as found in the salt 
flats, where it has been possible to measure the concentration of the 
ground water, and where the growth of crop plants is obviously impos¬ 
sible. 
The large series of physical and chemical measurements made by our 
predecessors makes it evident, however, that in all the habitats in which 
any considerable quantity of salt occurs the concentration of the soil 
solution must become very high when the soil moisture is much reduced 
by the drying concomitant with the advance of the season. 
Investigations on native vegetation, in part published and cited in 
the introductory section of this paper, but in large part still un¬ 
published, have shown that the osmotic concentration and specific 
electrical conductivity of the tissue fluids of native vegetation bear 
an intimate relation to the aridity or salinity of the region. It is 
but a short—and a very logical—step from this conclusion, which rests 
upon a large body of facts, to the hypothesis that a fundamental pre¬ 
requisite for the survival of a plant species, wild or cultivated, in arid 
regions is a much shortened growth period, a highly efficient water- 
storage mechanism, or a high osmotic concentration of its tissue fluids. 
The generally high osmotic concentration of the tissue fluids of the 
less ephemeral 6 plant species of the region and the enormous concentra¬ 
tions attained by A triplex confertifolia and A triplex nutallii ( 21 ) when 
growing in such localities is ample evidence for the necessity for very 
great osmotic concentrations of plant tissue fluids as a prerequisite for 
perennial growth in most of the^region considered. 
« The lower osmotic concentrations are found in the species which persist for but a brief period during 
the spring when growth conditions are more favorable than they can continue to be for the maturing of the 
most agricultural plants, or in the mountains where conditions are suitable only for grazing. 
