TOPOGRAPHICAL. ECOLOGICAL, AND TAXONOMIC NOTES. 28& 



being provided by tlie "Coast Tea-tree" Leptospermum 

 Icevlgatum F.v.M., which is frequently assembled in a close 

 formation, occasionally so densely packed as to exclude all 

 except liane growth, or a few exceptionally shade-tolerating 

 species. This habit is simulated by Casuarina suberosa 

 Otto and Dietr., which, on the headland at Oronulla, has 

 formed so close a thicket that the only intruder on its 

 privacy is the creeping Hydrocotyle hirta R. Br. Of these 

 arboreal societies, Banksia integrifolia L. f. occasionally 

 extends in belt formation* B. serrata L., Melaleuca leuca- 

 dendron L. var. albida (Sieb.) E. Cheel MS., (Melaleuca 

 Smithii R. T. Baker), Eucalyptus corymbosa Sm., etc., 

 usually forming clumps or groves. Two arboreal species 

 are confined to the rocky hillside, the remainder of the 

 sylvatic vegetation bestowing equal favour upon dune and 

 headland. 



The principal factor affecting the vegetation on the sea- 

 board, is the on-shore wind, whose mechanical action 

 retards arborescent growth and induces nanism, its 

 sustained attack compressing the shrubs on the exposed 

 front of the dune embankment, or rocky headland, into a 

 horizontal growth. Its capacity for quickly carrying off 

 moisture, promotes rapid transpiration, resulting in the 

 survival of plants with a xerophytic equipment. The wind 

 also minimises the stability of the soil by erosion, and 

 transportation, the dune vegetation in the region of exposure 

 responding by trailing, or spreading a carpet closely 

 appressed to the soil, by deep taprooting, or by framing a 

 rhizomatic network. The latter device also serves as a 

 protection against displacement by flood- waters, and acts 

 as a deterrent to the intrusion of fugitive plants. A con- 

 siderable share of the root ramification may also be debited 

 to the necessity for covering an extensive field of this 

 inhospitable region in search of a suitable food supply, the 



S -October 3, 19:7. 



