104 



It rarely exceeds 15 feet in height and fre(|nently has several slender stems 

 terminating in a dense canopy of foliage-bearing shoots. The association is 

 generally an open one, other shrubs being: — 



Rhagodia baccafa Wcstriiigia rigicla, var. dolichopJiylla 



Corrca spcciosa Myoponiiii dcserfl 



Spyridiuui crioccphalnm Olcaria rai)ntlusa 



P'uncUa serpyllifolia 



The soil is a coarse granitic sand of much the same type as in the Casuariiia 

 woodland, but lacking the dark colour due to humus. It was bare of annuals in 

 January, nor could any sign of their dead remains be seen. A small number of 

 perennial species occurs in open places; these are plants characteristic of earlier 

 phases of the succession, e.g.: — 



Poa cacspitosa, var. Billardieri Sclcranthus puugcns 



Mesemhryantlicmuui acqitilafcrolc Pclargniiiiiiu anstralc 



Atriplcx paliidosuiii occurs in several open areas on the north side of 

 Main Creek as small inliers of saltbush plain (pi. viii., fig. 2). 



III. Olcaria-Lcncopogon thicket. 



A mixed community of shrubs, of which Olcaria ramidosa and Lcncopogon 

 Richei are the most important, exists on some of the lower slopes of the hills 

 of Northern Island, covers South Hill so far as exposure will allow, and occurs 

 also on Middle Island. More than one association is probably involved here, 

 but there is so much intergradation between the dififering habitats owing to 

 exposure, the broken nature of the ground, etc., that it is inadvisable to attempt 

 to define dififerent communities. 



The conditions of development of this Olcaria-Lcucopogon associes are 

 generally similar to those producing Casuarina woodland or Melaleuca scrub 

 at higher levels or where exposure is less severe. The soil is granitic sand held 

 in clefts of various depths, or terraces between the boulders or tors. Exposure 

 to heat and wind is greater than in the case of the two former communities, 

 while the soil is less stable owing to the more rapid weathering of the rocks. 

 The efifect of aspect and exposure on the development of this thicket has been 

 referred to in the case of East Hill (pi. iv., fig. 1). 



Other plants noted as occiu'ring in this community are : — 



Rhagodia baccata Corrca speciosa 



Eiichylaeua iomcntosa Mcseiiibryajitlicnniiii acqiiilatcralc 



Lepidium foliosuui Alyoporiitiii iiisiilarc 



On Middle Island and portions of Northern Island, near the head of ]\Iain 

 Creek and the south-west corner of the island generally, it is not possible to 

 define the communities even within the broad limits mentioned above. The 

 conditions in these localities are less stable owing to weathering of the rock, 

 extremes of exposure to the south-west gales alternating with comparative pro- 

 tection in hollows of the rock, the possible influence of spray, and so on. In 

 addition to the plants mentioned others are present that are the earliest colonists 

 of rubble soil. Such are : — 



Poa cacspitosa, var. Billardieri Pelargoiiiuiii aitstrale 



Sclcraiithits pitiigois 



Occasionally are found bushes or local patches of Alriple.v pahidosimt which 

 typically occurs as the dominant in a distinct communitv. 



