106 



slone. The flow of water down these channels would be very intermittent even 

 in the wet season, owing to the small catchment and non-retentive nature of the 

 soil covering parts of it. Scrapings of the dried algal growth showed only 

 Tolypoihrix sp. 



Watercourses. 

 The two species of Melaleuca are the most prominent plants of watercourses 

 on Pearson Islands. Melaleuca parviflora occurs along the beds of the two 

 fresh water creeks, North Creek (pi. ix., fig. 2) and the tributary to Main 

 Creek. It is not, of course, confined to this habitat, but when growing beside a 

 watercourse descends further from the hills on to the plain below. 



Melaleuca hahnaturorum is restricted to the course of Main Creek, which 

 it follows from source to near the mouth (pi. vi., fig. 2, and pi. vii., fig 1 j. This 

 is a paper bark tea-tree, well known from habitats elsewhere in South Aus- 

 tralia to have a high salt toleration. The water flowing down Main Creek 

 is derived from two sources. Drainage from 781 Hill and the tors at the 

 south-western corner of the Northern Island provides the bulk of it, but sea spray 

 contributes some water as overflow from the granite basins described above. 

 The upper course of the creek is indefinite and appears to be shifting. No special 

 creek flora can be described in connection with it. The plants growing in the 

 wide indefinite channels have been referred to under the Pelargouiuiu-Mesciu- 

 bryanthernum-Poa community. 



Drainage channels are common near to the bare granite slopes in other parts* 

 of the islands. Ulothrix sp. covers the soil, and growing amongst it occur such 

 ephemerals as :— 



Cenirolepis sp. Cotula coronopifolia 



Calaingrostis filifolia 

 Such channels do not influence to any appreciable extent the flora of perennial 

 plants around them. 



Saltbush Formation. 

 Atriplex paludosum dwarf shrubland. 

 A typical saltbush formation is developed on several parts of Northern and 

 Southern Islands. The principal habitat is upon the gently sloping plains that 

 occur at the foot of the steep rocky slopes. The soil of these areas is composed 

 of fine granitic rubble, almost sandy in texture. The free open soil is one that, 

 in spite of its humus content, has only a low water-retaining capacity. In 

 January many of the shrubs were obviously showing the need of water, the 

 leaves were often flaccid, and the older ones falling oft'. 



The temperature and insolation factors on these exposed plains must be 

 severe. It is probable that the light grey-green colour of the Atriplex leaves 

 niay be correlated with light protection. 



The Atriplex bushes stand 12 to 18 inches high, and in places form an 

 almost closed community (pi. vi., figs. 1 and 2). Only one other plant, a 

 small annual composite, was found on the typical saltbush plain. 



Atriplex paludosum appears to be a plant that will not tolerate much 

 moisture in the soil. Its specific name is not at all appropriate to its South xA.us- 

 Iralian habitats. Depressions on the plains were colonized by Rhagodia crasst- 

 folia (pi. vii., fig. 1). The same plant replaces Atriplex at the base of the steep 

 rocky rises above the plains, w'here the influence of drainage from the slopes 

 above will be most pronounced (pi. vi.. fig. 1). 



It will be noticed from the analyses of soil Sample 2 (NaCl=-20 per 

 cent.), that Atriplex paludosum growing on Pearson Island is not a halophyte. 

 It was absent from the flora of the basins at the head of Main Creek, where the 

 soil was very salt (Sample 6). though it occurred at their edges, where the 

 salinity was even lower than in the Atriplex plain (Sample 5. NaCl = T5 per 



