107 



cent.). The Atriplcx paludosmn association observed is a xerophytic com- 

 munity, not a halophytic one. 



Though saltbush dwarf shrubland grows best on granitic soils, it is not 

 confined to them. It is developed upon the higher levels of the travertine 

 plateau on Northern Island, and at the eastern end extends almost to the coast. 

 Exposure to sea spray is less here than on the other travertine areas. On such 

 soils the community tends to be a mixed one, Lyciuni australe, Lepidiiim, 

 foliosum, and Senecio lautus being present. The Atriplex bushes are more 

 stunted than in the pure community, with bare soil between them. 



On the west side of Main Creek, i.e., the dry north facing slope, patches of 

 Atriplex occur as inliers in the open shrub community of Melaleuca parviflora 

 described above (pi. vii., fig. 2). 



Travertine Limestone Communities. 



It has been remarked before that the principal limestone areas can be recog- 

 nized at once by the difi^erent type of vegetation that they bear. These com- 

 munities are grouped together as members of a separate series. No climax is 

 distinguished, and it is possible that were a larger series available the com- 

 munities would find their place as serai units in a formation culminating either 

 as Atriplex dwarf shrubland or Melaleuca parviflora scrub according as climatic 

 factors were more or less xerophytic. 



In regard to the travertine limestone habitat on Pearson Island, one observes 

 that in addition to the obvious feature of calcium carbonate in the soil there 

 must also be considered the shallow depth of soil overlying the limestone deposit, 

 exposure to light and wind owing to the unbroken nature of the terrain, and, in 

 some cases, e.g., the soil sample analysed, No. 1, an appreciable amount of 

 sodium chloride. In spite of these features, it is not possible to recognize such 

 a definite limestone community as that of Frankenia fruticulosa seen on Franklin 

 Island. ""' Though the travertine areas may be recognizable at once owing to the 

 difference in the plant covering, it is less easy to define wherein that difference 

 lies. It is usually one of degree and varying proportions of plants occurring 

 elsewhere on the islands, rather than one due to the presence of plants limited 

 in their distribution to these areas. Three communities are sufficiently distinct 

 to be briefly noted : — 



I. Mat Plant Community. 



A community consisting of prostrate or semi-prostrate dwarf perennials 

 occurs on most of the plateaux (pi. viii., fig. 2). The majority of the plants 

 are more or less succulent, and many of them have their leaves coloured owing 

 to the presence of anthocyanin pigments. The general effect thus produced is 

 most striking, resembling some gigantic carpet worked in grey (Atriplex), 

 orange or red ( Mesemhryanthemum) , maroon (Threlkeldia), grey-green 

 (Enchylaena), or olive-green (Frankenia). The species noted are: — 



Che)iopodium sp. {affin. micro phylhmi) Atriplex cinereum 

 Enchylaena tomentosa Mesemhryanthemum australe 



Threlkeldia diffusa Frankenia pauciflora 



II. Cliff Faces. 



The seaward edges of the plateaux end in low cliffs 4 to 8 feet high ; at 

 the margin of the cliff faces grow :- — ■ 



Arthrocnemum halocnemoides, var. Suaeda australe 



pergranulatiim Tetragonia implexicoma 



Salicornia australe Nitraria Schoeberi 

 Enchylaena tomentosa Frankenia pauciflora 



(6) Osborn, T. G. B., loc. cii., p. 201, 1922. 



