399 



12 inches of soil was sufficient to determine a distinctly halophytic flora. Of 

 this '68 per cent., however, 13 per cent, was sodium chloride. In such a con- 

 centration of sodium ions the halophytic nature of the flora is more pronounced 

 than in a soil with 1'30 per cent, of total soluble salts of which only 05 per cent, 

 is sodium chloride (sample No. 9). Under such conditions Atriplex vesicarium 

 (?var.) is able to persist on a flooded flat. 



The soils of two distinctly halophytic communities have been analysed, 

 samples Nos. 7 and 8. On neither of these were perennial Chenopodiaceae other 

 than members of the Salicornieae growing. Nillinghoo Lake (No. 7), with 

 660 per cent, total salts and 352 per cent, sodium chloride had a pure com- 

 nmnity of Pachycornia tenuis. Koonamore Gypsum Salt Lake (No. 8) had a 

 total salinity of 4 '97 per cent., but with '68 per cent, only of sodium chloride. 

 This area had dense thickets of Arthrocnemum spp. The bare ground between 

 the bushes had such annual Chenopodiaceous plants as Babbagia aero pt era and 

 Atriplex spongiosum. These species, especially the latter, have a wide dis- 

 tribution and occur in several communities. They are not consistently halo- 

 phytic, but are elements in the pioneer floras of several habitats in the district. 



In conclusion, we have attempted to show that large portions of the interior 

 of Australia are occupied by a distinctive type of arid flora. Other arid areas 

 have, as is well known, developed their characteristic floras of xerophytes ; 

 the Karroo flora, in which the Crassulaceae are exceedingly prominent, is one 

 very familiar example. In Australia the Crassulaceae is a family of minor 

 importance, but the Chenopodiaceae is represented by numerous pronouncedly 

 xerophytic species. 



While the members of many arid floras have developed succulence as a 

 characteristic structural feature, tending to the conservation of a considerable 

 water balance in the plant, the Australian Chenopodiaceae are not specialized in 

 this particular direction. On the other hand, they have attained a remarkable 

 degree of xerophytism, by reducing their transpiration ratio to a minimum. <^^^^ 

 A feature of the climate in arid Australia is the quantity of "ineffective rain- 

 fall." ^^®) It seems probable to us that the leaf mechanism of the Chenopodiaceae 

 with the large water vesicles of Atriplex, or the peculiar hairs of Kochia, may 

 be connected with the utilization of this rainfall, which is ineffective so far as 

 the roots of perennials are concerned. We shall publish observations on this 

 question shortly. 



DESCRIPTION OF PLATES XXXV. and XXXVI. 



Plate XXXV. 



Fig. 1. Atriplc.v vesicarium community at Koonamore (Alderman's). 



Fig. 2. Mixed community of Mallee eucalypts (E. oleosa) with Atriplex spp. and 

 Kochia scdifolia about equally abundant in the ground flora. Dilkera. 



Fig. 3. Kochia planifolia community on plains near Curnamona. Bushes of Ercmophila 

 glabra forming scattered thickets on the horizon. 



Plate XXXVI. 



Fig. 1. Arthrocnemum halociicmoides, var. pergramilatum, community on gypsum salt 

 lake near Koonamore Head Station. In the foreground are scattered annuals, e.g., Babbagia 

 acroptera, Atriplex spongiosum, etc. 



Fig. 2. Mixed community with Arthrocnemum halocncmoides, var. pergranulatum, and 

 Atriplex haUmoides, A. spongiosum, and A. limbatum on flat flooded by overflow from gypsum 

 salt lake near Koonamore Head Station, seen in fig. 1. 



Fig. 3. Pachycornia toiuis community on the bed of salt lake at Nillinghoo Lake, Koona- 

 more. The white efflorescence of gypsum can be seen between the dwarf bushes. 



(18) Wood, loc. cit., 1923. 



(i») Cannon, W. A., loc. cit., p. 47, 1921. 



