394 



temperature, filtering through a Chamberland-Pasteur candle and an aliquot 

 portion examined for total salts and chlorides. The values obtained are con- 

 sistently low except in soils from the salt lakes or their overflow. 



The loss on ignition is low and varies little, the highest value being in the 

 salt lake. The figures in this column represent the loss obtained after igniting 

 the soil at a red heat, moistening with saturated ammonium carbonate to convert 

 lime into carbonate and gently igniting to expel excess of ammonium salts. It 

 represents, therefore, humus plus combined water. 



The pH values were determined colorimetrically with Clark and Laub's 

 sulphonephthalein indicators. The values are constant for Atriplcx communities, 

 viz., 7'6 to 7'8. The eflfect of the abundance of soluble salts in the lakes is 

 reflected in a higher value for the pH, 8'2 in each case, approximately that of 

 sea water. The last column gives a description of the soils based on microscopic 

 examination. 



Distribution of Chlorides. — It will be seen from soils Nos. 10-12 that the 

 percentage of sodium chloride increases and that of total salts decreases wuth 

 depth, also that chlorides form a small proportion of the total salts. In soil 

 No. 7 from Nillinghoo Lake over one-half of the total salts are chlorides, even 

 in the surface layers. The cause of the difference in distribution is explicable 

 when the physical nature of the soils is examined. Nos. 10-12 are very fine 

 sands, No. 7 is a coarse sand. The soluble sodium chloride, while more easily 

 leached from the coarse sand than from the fine, is conversely able to rise in 

 solution much more quickly in the coarse than in the fine. The less soluble 

 the efflorescent calcium sulphate becomes accumulated at the top and this is 

 quickly diluted with sodium chloride in the Nillinghoo Lake soil. 



BlOTIC. 



A detailed consideration of the biotic features will not be given in this paper. 

 The indigenous mammalian fauna appears to have little effect on the plant life. 

 The insect fauna, on the other hand, at times exercises great influence, e.g., in 

 plagues of grasshoppers or caterpillars. Biotic factors of moment are the in- 

 cursive white man with his domestic animals and vermin, especially rabbits. 

 All these animals affect considerably the constitution or facies of a flora which 

 in its undisturbed condition was in a state of very delicately balanced equilibrium 

 owing to the severity of climatic factors. 



Vegetation. 



Over so large an area many plant communities exist, though owing to the 

 relatively even nature of the terrain, the similarity of the climatic and soil 

 factors, the same community may extend for 100 square miles or more without 

 notable change other than that occasioned by a local swamp. Such changes as 

 do occur are often puzzling, especially the presence or absence of such trees as 

 mallee eucalypts, black oak (Casuarina lepidophloia), sandalwood (Myoporum 

 platycarpiim), or mulga (Acacia aneura), as an overgrowth of trees above the 

 saltbush or in cases even replacing it. Into the inter-relationships of the com- 

 munities recognizable in the field we do not propose to enter in this paper ; a 

 lew of them only are described for purposes of comparsion with the halophytic 

 vegetation of the flats. 



Saltbush — Atriplcx vcsicai'ium community. 



This is a dwarf shrubland of half-woody bushes 40-60 cms. or more in 

 lieight. The bushes grow close together but rarely touch, the area of bare ground 

 between them depending on the vigour of the plants, the amount of rainfall 



