12 



29 



120 



254 



A. paludosum was in a wilting condition. In the Arthrocnemum halocnemoides 



zone the proportion of salts to water is slightly less than in the case of A. 



arhusciila. But, whereas, the latter plants were growing thriftily, the former 



were markedly collapsing, the cortex of the plants as collected being shrunken 



and wrinkled. 



If, however, we take the proportion of salts to water in the saturated soil, 



using the percentages given on page 249 a different result is obtained. The 



ratio of salt to water becomes : — 



Arthrocnemum halocnemoides . . . . . . 1 



Atriplex paludosum . . . . , . . . . . 1 



A. stipitatum . . . . -. . . . . . . . 1 



This, we believe, expresses more accurately the degree of salinity of the 

 soil solution in the respective zones during the wet season. They confirm our 

 conclusions that the zonation of the vegetation observed is correlated with a 

 decrease in the salinity of the soil, and that this is accompanied by an increasing 

 aridity of the environment. 



The figures given by us for the total salinity of the different zones, high 

 though they are, are actually less than the percentage of total salts in the soils 

 of "alkali lands" of the United States of America. Hilgard'*^^'^) gives his figures 

 as pounds per acre feet. We have taken the results as given by him and 

 converted them to percentages of "wet" soil by taking 3,750,000 lbs. as the weight 

 per acre foot of soil (vide Hilgard, p. 444). The results for certain of the char- 

 acter plants of the alkali lands are : — 



Allenrolfia occidentalis . . . . 132 per cent, total salts 



Salic ornia subterminalis 

 Frankenia grandiflora . . 

 Suaeda Torreyc^ia 

 Sarcohatus vermiciilatiis 



118 



7-5 

 3-5 

 15 



It is for comparison with these figures that we have given the percentage 

 of salts to wet soil in our table on page 248. 



The zonation of the vegetation around a salt lake in an arid region has been 

 studied in some detail by Kearney and his co-workers ^-^^^ in Tooele Valley, Utah. 

 The observations made by us are in general agreement so far as the zoning of 

 comparable plants is concerned. It is interesting to notice that at Tooele the 

 salt swamp plant is Allenrolfia, and that Atriplex confertifolia grows on the 

 less salt portions. This plant, from its general relations, appears to correspond 

 to our A. paludosum. Atriplex stipitatum, the chief constituent of the saltbush 

 area (using the term in its generally accepted Australian sense) corresponds 

 rather to the North American sage brush, Artemesia tridentata; that is, to a' 

 plant of arid regions with only a low salt concentration in the soil. 



EXPLANATION OF PLATE XX. 



Fig. \. General view in Arthrocnemum arbuscula zone, showing a bare creek to right. 

 The mounds and bushes in the middle distance are "shell islands." On the horizon are the hills 

 of Yorke Peninsula across Gulf St. Vincent. 



Fig. 2. Creek in the Arthrocnemum halocnemoides zone. The figure to the left stands 

 on a raised bank, on which are bushes of Atriplex paludosum. The figure to the right is in 

 the creek bed ; in this grow bushes of Arthrocnemum arbuscula. 



Fig. 3. Junction of the Atriplex paludosum zone and the Arthrocnemum halocnemoides 

 zone, seen in the lower land to the right. 



(14) Hilgard, E. W., loc. cit., p. 549. 



(15) Kearney, T. H., L. J. Briggs, H. L. Shantz, J. W. McLane, and R. L. Piemeisel, 

 "Indicator Significance of Vegetation in Tooele Valley, Utah," Journ. Agr. Research, i., pp. 

 365-417, 1914. 



