Mar. 22 , 1924 
Tissue Fluids of Indicator Plants 
895 
At the time the field work was done the writers were not acquainted with 
Mason’s (26) attempt to correct conductivities for the viscosity of the 
solution by determining the increase in conductivity due to the addition 
of a given amount of KC1 to the tissue fluids. The conductivities as 
given here are, therefore, the raw values, wholly uncorrected for the 
viscosity of the sap. It is perhaps obvious that it would have been 
impossible in dealing with plants with such a high chlorid content as 
those of the Great Salt Lake region to utilize KC 1 in determining the 
influence of viscosity on the conductivity, but it may be unfortunate 
that some other salt could not have been employed for this purpose. 
Some measure of the relative importance of salts and organic solutes 
in determining the osmotic concentration is highly desirable. We have 
used for the purpose the ratio of specific electrical conductivity, K, 
to freezing point lowering, A. 
Chlorid content was determined on samples of sap pipetted in the 
field and preserved in sealed tubes for subsequent analysis. The analyti¬ 
cal method employed is described elsewhere (25). The results are 
expressed in terms of grams of chlorids Cl per liter of tissue fluid. 
PRESENTATION OF DATA 
In the presentation and analysis of the measurements we have fol¬ 
lowed as closely as possible the classification of plant associations rec¬ 
ognized by Kearney and his coworkers (24). Since growth forms have 
been shown to be differentiated in their sap properties by our earlier 
studies on the vegetation of the Arizona deserts ( 12 ) and by more recent 
investigations in humid (17) and mesophytic (20) habitats, it is essential 
that the species of each habitat be classified according to growth form. 
Since the herbaceous species are chiefly evanescent, it would be improper 
to include them with the ligneous species in obtaining a general average 
for the association unless it be shown that the concentrations of the 
tissue fluids of the ligneous species remain the same throughout the 
season. 
Because of the concentration of the soil solution due to drying, and 
due also, perhaps, to some extent to the accumulation near the surface 
of salts brought up from lower levels, it seems altogether unlikely that 
concentration of the tissue fluids of the more permanent species of the 
halophytic vegetation will remain the same throughout the season. 
Such a result is quite contrary to the findings of Cavara (r) who in¬ 
vestigated the changes in a number of halophytes with the march of the 
season. It is therefore necessary in the analysis of the date to arrange 
the determinations chronologically. It is impossible in one year’s work 
to obtain satisfactory data sufficient in quantity to show the seasonal 
change in each of the habitats for even the more important species. 
The results of the present series must serve as merely a rough indication 
of seasonal change. 
An earlier discussion of the plant associations of this region (24) 
emphasized the sharpness of demarcation which characterizes their 
distribution. In our discussion of the constants it may appear that there 
have been considerable difficulties in deciding to which association some of 
the samples should be assigned. This is largely due to the fact that from 
many sides the narrow transition zones, or those which afford a complex 
of physical conditions, are biologically the most interesting. Such con¬ 
ditions are found, for example, in the washes through the sagebrush 
