398 



being dominant. These hill slope communities are of essentially similar type to 

 those described by Cannon at Copley and Collins at Broken Hill. 



The vegetation of the plains and peneplains is composed of a number of 

 communities in which one species or another of Atriplex or Kochia is very 

 prominent, usually being dominant, or less frequently co-dominant, or even 

 subordinate to mallee eucalypts. The conditions under which these communities 

 grow are remarkably uniform, considering the area over which they are dis- 

 tributed. There is a gradual but progressive aridity as one proceeds north. 

 Concurrently with the decrease in rainfall is its greater unreliability and also the 

 diminishing importance of the winter rains (text fig. 2) . Under such conditions the 

 mallee eucalypts become less important, and finally, towards the north of the 

 district, disappear entirely. At Koonamore they are limited to selected areas, 

 the conditions obtaining there being apparently those of the ecological limit in 

 the distribution of mallee. This appears also to be the case at Broken Hill. 



The Chenopodiaceae, on the other hand, become increasingly important as 

 one proceeds north. Of the many communities developed that are dominated 

 by Chenopodiaceous plants we have referred here only to the more prominent. 

 We intend at a later date to describe these in greater detail, together with some 

 others, and to discuss the trend of succession in the district. The communities 

 developed have, on the whole, a stamp of distinct uniformity, whether they 

 have Atriplex vesicarium or other species (e.g., A. paludosum or A. stipitaiinn), 

 Kochia planifolia, or even K. sedifolia, as dominants. 



Analyses show that the soils are of much the same type (samples Nos. 1-6). 

 They are low in salts, whether total salts or chlorides. There is also, so far as 

 we have determined, little variation in the water-retaining capacity. Briggs and 

 Schantz ^^^^ have shown that the amount of water a given soil is capable of hold- 

 ing varies from 232 per cent, in coarse sand to 69'5 per cent, of the dry weight 

 of the soil in the case of clay loam. The range of saltbush-bluebush soils show 

 an average water-retaining capacity at saturation of 36 per cent., which 

 approximates to that of fine sand. Atriplex limbatimi is able to grow in soil 

 with only 25-29 per cent, of water at saturation. This is near the limit of the 

 range shown by Briggs and Schantz, and suggests that A. limbatum is able to 

 grow with a lower water supply than A. vesicarium or the other perennial species. 

 A. limbatum, which is a shallow rooting species, was the only perennial saltbush 

 growing on the flat (samples Nos. 10-12) flooded by water overflowing from 

 the Gypsum salt lake near Koonamore. This area was sufficiently saline to 

 determine a halophytic flora, the total salts ranging from 85 per cent, in the 

 surface soil to '46 per cent, at a depth of 6-12 inches. The sodium chloride, 

 which in the surface soil is only 06 per cent., reaches '22 per cent, at the greater 

 depth. The boundaries of these flooded areas are difficult to define, and along 

 their edges a mingling of communities takes place. Thus Atriplex vesicarium 

 (? var.) was found growing near to a typical Arthrocnemum halociiemoides, Ydir. 

 pergranulatum, community in soil with 1'30 per cent, total salts, of which, how- 

 ever, only 05 per cent, was sodium chloride (sample No. 9). A point which 

 requires further investigation is the calcium-sodium ratio. Excess of calcium 

 ions do not appear to exert so marked a toxic efl^ect as sodium ions. Warming '^^'^ 

 has shown that the extent to which a soil dries out influences its halophytic 

 nature. "When the soil dries readily a small amount (perhaps 1 per cent.) of 

 salt may expel all plants save halophytes, whereas if the soil does not dry readily 

 perhaps 2'5 per cent, of salt is required to act in the same manner.' In the 

 flooded areas (samples Nos. 10-12) only '68 per cent, total salts in the first 



(16) Briggs and Schantz., H. L., Botan. Gazette, liii., p. 31, 1912. 

 d") Warming, E., loc. cit., p. 218. 



