392 



Temperatures. — No detailed temperature data are available. The summer 

 shade maxima are known to be often over 100° F. A surprising feature is 

 the amount of frost in winter, particularly in the wide, flat valleys of the 

 peneplain. 



Other factors, such as wind and insolation, all increase the aridity of the 

 environment. The relation of these to transpiration is described by Wood ^^^^ 

 'n an account of some experiments conducted at Dilkera. 



Edaphic Factors. 



In a region without any striking variation of physiographic features, and 

 showing little abrupt discontinuity in its climatic factors, the edaphic factors are 

 of great importance in determining differences in vegetation. Even these factors 

 are remarkably uniform over great distances. The great depth of soil found on 

 the plains of this region is a feature similar to that observed in man}'- other 

 arid regions. Wind sorting is one of the factors responsible for the production 

 of different soil types. As a result of its action there are produced sand ridges 

 alternating with flats of finer-grained soil. These occur on a huge scale towards 

 Lake Frome, where the alternation of sand ridges colonized by Casnarina 

 lepidophloia with saltbush covered flats gives a distinctive stamp to the landscape. 

 This is popularly called "black oak ridge country." On a smaller scale a similar 

 result may be observed by lakes or swamps which frequently have a sand ridge 

 in proximity to the bed of the lake. The relatively rapid change in soil type 

 observable here is accompanied by an instructive change in vegetation (c.f. soil 

 samples Nos. 13-15). 



In this paper a selection of 15 of our soil analyses is given. These samples 

 are chosen either to show the change in edaphic conditions w'hen passing from a 

 halophytic community to saltbush, or to show the essential similarity of soils 

 over the whole saltbush area. This last feature applies to the series 1-6. As 

 No. 5 we have repeated for purposes of comparison our analysis of the soil 

 supporting a saltbush community at Port Wakefield, which lies outside the area 

 under immediate discussion. 



Methods. — The soil samples were collected with the aid of a sampling tool. 

 Except where otherwise stated, cylinders of soil were taken from the first 

 9 inches of ground. The samples were placed in air-tight tins for conveyance 

 to the laboratory, where the procedure was as outlined in our previous paper. "^^^^ 



The first column of the accompanying table of soil analyses gives the per- 

 centage of water present in the wet soil and is a measure of the water relation 

 existing in the soil at the time of collecting. The columns for water in the 

 dry soil and for saturation water run parallel to one another, e.g., the sandy 

 soils 14 and 15 with low saturation water show low water content in the air dry 

 soil, saltbush soils have a saturation percentage of about 36 per cent., and the 

 effect of clay in the lake soil No. 8 is reflected in the high saturation (41 '3 per 

 cent.) and the high water retaining capacity of air dried soil (88 per cent, of 

 water). The saturation water was determined as described by us in our paper 

 on the Port Wakefield soils, <^^*^ but in this case the tubes were allowed to stand 

 in water until a constant increase was observed due to the absorption of water. 

 This constant increase is, as a matter of fact, attained almost immediately the 

 water reaches the top of the soil column. 



The soluble salts were determined, as in our previous work, by shaking 

 25 grms. of soil with 250 c.c. of water at intervals over 24 hours at constant 



(12) Wood, J. G., Trans. Roy. Soc. S. Austr., vol. xlvii., p. 259, 1923. 



(13) Osborn, T. G. B., and Wood, J. G., loc. cit., 1923. 



(14) Osborn, T. G. B., and Wood, J. G., loc. cit. 



