TOPOGRAPHICAL, ECOLOGICAL, AND TAXONOMIC NOTES. 301 



retarded, it spreads trailing branches to retain the sand in 

 its vicinity and intercept the drift from the beach, using 

 the collected material as a support for its heavy limbs, and 

 relieving the ascending stem of the burden of supporting 

 the unwieldly lateral growths. 



One of the twiggy "Salt-bushes," Rhagodia Billardierl 

 R.Br., is prevalent on the dune flat. Plants of this species 

 when standing alone, build up a divaricately branched, 

 hedge-like structure, but when growing in the vicinity of 

 stout upright shrubs, they invest them, trailing over their 

 stems and branches. One of these plants was noted to 

 have covered the trunk of a dead Banksia to a height of 

 eight feet. On the dune it usually coats its leaves with a 

 waxy varnish, but on the rocky escarpment of the head- 

 land this protective device is not so much in evidence, and 

 is occasionally — in very exposed situations — replaced by a 

 mealy tomentum. 



The cosmopolitan "Couch-grass," Cynodon dactylon A. 

 Rich., spreads a closely matted lawn on the plateau, creep- 

 ing out to within a few yards of the edge of the dune 

 embankment, the "Buffalo-grass," Stenotaphrum ameri- 

 canum Schr., forming a flanking carpet, or, in places where 

 garden refuse has been tipped, intruding on the Couch. In 

 the frequent encounters between these two favourite lawn 

 grasses, the question of supremacy is decided by the quality 

 of the food supply, the quantity of moisture available and 

 the physical condition of the soil. On the impoverished 

 permeable sandy soil of the dune, the Couch will hold its 

 own, but in the stiff clayey soil of the Wianamatta Shale 

 the stouter subterranean stems of the Buffalo overpower 

 the slender rhizomes of the Couch, and its broad heavy flag 

 will exclude the light from the weaker grass, and eventu- 

 ally suppress it. 



Though both grasses advance to the front of the dune 

 plateau, they cannot, either singly or in association, main- 



