397 



areas at Port Wakefield. Soil from a typical A. halocnemoides, var. pergranu- 

 latum community is analysed as sample 8. The total salts is high (497 per 

 cent.), though sodium chloride is only 68 per cent. At Port Wakefield 

 A. halocnemoides, var, pergranulatum, was found growing above the zone 

 occupied by the typical A. halocnemoides as a few isolated bushes in the Atriplex 

 paliidosum consocies. The variety, therefore, does not seem to be able to tolerate 

 an excess of sodium chloride. PI. xxxvi., fig. 1, shows this community at 

 Koonamore. The plants form thickets in which Arthrocnemum leiostachyum, 

 a stouter growing species, is also present, but in small quantity. The gypsum- 

 saturated ground between the bushes is bare, only a few annuals being present, 

 including Bahhagia acroptera, Atriplex spongiosutn, M esembryanthe mum australe, 

 and Cap sella elliptic a. 



The boundaries of such swamps are ill-defined, because in time of excep- 

 tional flood, the waters may transgress their proper limits, submerging the sur- 

 rounding country for miles. These transition zones are occupied by Arthrocnemum 

 halocnemoides, var. pergranulatum, Frankenia serpyllifolia, Bahhagia acroptera, 

 Heliotropum cnrassavicum., Atriplex limhatum, with which such annual species 

 as Atriplex spongiosum, A. halimoides, Bassia patenticuspis, B. obliquicuspis, etc., 

 compete (pi. xxxvi., fig. 2). The species of Atriplex, especially A. spongiosum, 

 are pioneer plants in many situations. The same may be said of the Bassias, 

 which are a prominent feature in early phases of succession in the area.^^-^^ The 

 soil analyses of this flooded area, samples 10-12, show that it is quite possible 

 for the shallower rooting annuals to be relatively non-halophytic compared with 

 deeper rooted perennial species growing alongside them. The salt content in the 

 first 2 inches of soil is '85 per cent, total salts, sodium chloride 06 per cent., 

 while at a depth of 6-12 inches, the total salts are '46 per cent., of which '22 per 

 cent, is sodium chloride. Samples .13-15 were taken above and below an ecotone 

 line dividing the flora of a flood plain of the type described above from that 

 of a sandy, limestone rise. The total salt content falls from '34 per cent, to 

 '06 per cent. The water at saturation shows that the water-retaining capacity of 

 the soil also decreases markedly. The change in the vegetation at such a junc- 

 tion is abrupt. The Arthrocnemum disappears first, then the annual saltbushes, 

 Atriplex limhatum persisting higher up the rise. On the sandy rise itself occur 

 Acacia Oszvaldii, Myoporum platycarpum, Rhagodia spinescens, Atriplex vesi- 

 carium, and annuals, e.g., Tetragonia expansa, Zygophyllum ammophilum, etc. 



Pachycornia tenuis community. 



This plant forms a monospecific community on the floor of a large lake at 

 Nillinghoo, near Koonamore (pi. xxxvi., fig. 3). The plants are dwarf, semi- 

 prostrate, succulent, and herbaceous. Gypsum can be seen as a white efflorescence 

 on the bed of the lake between the plants. The soil, sample 7, contains 6'60 per 

 cent, of soluble salts, sodium chloride being 3'52 per cent. At the margins of 

 the lake, Arthrocnemum halocnemoides, var. pergranulatum, appears, and finally 

 replaces the Pachycornia, which is the more salt-tolerant species. 



Discussion and Conclusion. 



In this paper we have given an account of the Chenopodiaceous plant com- 

 munities occurring in the plains and peneplains of the arid North-east of South 

 Australia. We have omitted reference to the vegetation of steep hill slopes, 

 because the communities developed in such situations do not bear immediately 

 upon the question under discussion. The Chenopodiaceae is relatively unim- 

 portant in such communities, species of Acacia, Eremophila, Zygophyllum, etc., 



(15) C.f. Collins, loc. cit., p. 253. 



