251 



tufts of roots that have a short duration is well known in the case of other 

 succulents, e.g., in the Crassulaceae. When collected, vegetative activity on the 

 part of A. halocnemoides appeared to be at a standstill, the plants were wilting, 

 showing obviously the effect of the long dry summer. 



The other two plants of the community were sufifering even more severely 

 from lack of water. The leaves of the Mesembryanthemum were flaccid, those 

 of Frankenia pauciflora were erect, parallel to the stems, and seemed dried up. 

 The plant had a much more stunted habit than is usual. Its branches rose 

 obliquely without the adventitious rooting observed when it grows in sandy 

 soil.<i'^) 



The consocies here described characterises most of the plain between the 

 actual salt swamp and the higher-lying salt bush area. It is clearly halophytic, 

 but is not permanent swamp ; it is rather of the nature of an "alkali plain." 

 Though the plants have a high salt toleration they are sharply defined from the 

 actual swamp species, which replace them in local depressions. 



Drainage channels. — Drainage channels, many of which are tidal at the 

 lower portion of their course, and most of which would be flooded at ordinary 

 spring tides, intersect the Arthrocnemiim halocnemoides zone described above. 

 They are conspicuous because they are colonized by A. arbuscida, which, owing 

 to its taller growth and green colour, stands out distinctly above the lower red- 

 brown of the A. halocnemoides. At the edge' of some of the channels A} 

 leiostachyum occurred. 



The upper portion of the beds of the channels is bare, cracked mud. Water 

 evidently remains for some time in local hollows, but these were all dry when 

 examined. Large sheets of a felt-like material composed of Cladophora sp. 

 were found in the hollows. 



Banks of the drainage channels. — The banks of the drainage channels in 

 the A. halocnemoides area are interesting because, in places, they tend to become 

 raised above the general level of the rest of the plain. This is due to an accumu- 

 lation of silt, debris, and shells that becomes banked up around the plants grow- 

 ing at the edges. Thus local "islands" occur fringing the channel. These small 

 local patches of higher ground are usually only a few yards in length and not 

 much more than a yard wide, but their edaphic conditions differ from the sur- 

 rounding plain (see soil sample No. 6). The soil is less salt, drier, and has 

 more organic matter in it. On such islands A. paliidosum appears. The grey 

 leaves of this plant are a striking contrast to the colour of the vegetation on 

 either side. The occurrence of these outliers of the Atriplex paliidosum consocies 

 is a matter of some interest, for it indicates the importance of edaphic conditions 

 in determining the distribution of the saltbush in the area (pi. xx., fig. 2). 



Mixed shrub community on shell islands. — Debris deposited by flood tides 

 accumulates not only besides the drainage channels but in various other places 

 over the actual swamp area (A. arbuscula consocies). Shells of a cockle (Chione 

 sp.) are most abundant, though a conical shell (Bittiiim sp.) is present in large 

 numbers. Great quantities of the shells may accumulate against some large 

 object' and form mounds several feet high and many square yards in area. Several 

 such islands were visited and will be briefly described. 



The earliest stage seen was in the salt swamp area close behind the mangrove 

 limit. There, a tree-trunk and other flotsam of the tide formed the basis of a 

 mound composed chiefly of shells. This was colonized by Nitraria Schoeberi, 



(12) Osborn, T. G. B., "Flora and Fauna of Nuyts Archipelago, No. 3. A Sketch of the 

 Ecology of Franklin Islands," Proc. Roy. Soc. S. Austr., xlvi., p. 194, 1922. 



