ARID PORTIONS OF SOUTH AUSTRALIA. 81 



pum, 5; Fusanus acuminatus, 7; Fusanus spicatus, 13; Acacia varians, 

 15; Eucalyptus rostrata, 20 to 26. As this is a portion only of the 

 species observed, no safe conclusion can be drawn from the relation 

 above them. It is of interest to note the relatively large leaf-area of 

 Eucalyptus rostrata and ^caaa varians, which are strictly confined to the 

 habitat of the washes. But the complete exposition of leaf-sizes of 

 such a habitat as the wash, however, would show great variation. 

 Thus Eremophila alternifolia is confined, and quite strictly so, to this 

 habitat, and it has the smallest leaves measured. It should be said, 

 in this connection, that a great reduction in the transpiring surface, 

 even to a condition of total aphylly, is not uncommon in species with 

 large water-requirement. The opposite condition, however, namely, 

 the occurrence of large-leaved species in dry habitats, does not take 

 place. Therefore, the general rule can probably be said to hold, that 

 there is a direct relation between leaf -size (or transpiration surface) and 

 water-relation, at least in an arid region such as that about Copley. 



VEGETATION OF SOUTHWESTERN SOUTH AUSTRALIA. 



In the brief discussion to follow, on the plants of the southwestern 

 portion of the state and on their environment, the vegetation of only 

 three stations along the line of the trans-Australian railway will be 

 considered, namely, Port Augusta at the head of Spencer's Gulf, 

 Ooldea not far from the western border, and Tarcoola about halfway 

 between the two. At Port Augusta the rainfall is about 10 inches an- 

 nually and at the other stations it is somewhat less. Port Augusta is 

 at sea-level, but Ooldea and Tarcoola each have an altitude of about 

 500 feet. In spite of the low topography and the small rainfall the 

 region is much more varied and interesting than at first might be sup- 

 posed. At the extreme west and extreme east are plains, and in the 

 mid-region low hills characterize the topography. Except for the 

 outcrops of pre-Cambrian rocks, of relatively small area, the region is of 

 the Cenozoic age; Recent to Pleistocene between Port Augusta and 

 Ooldea; and Miocene and Eocene west of Ooldea. With a single 

 exception, therefore, this portion of South Australia is geologically 

 much more recent than the far north. In the plains regions halo- 

 phytes are the dominating plants, and in the hilly mid-region there is a 

 large variety of species which occur in larger numbers than might be 

 supposed, judging from the rainfall alone. They all, however, reflect 

 the severity of the environmental conditions under which they and 

 their ancestors have developed for an immense period of time. 



VEGETATION AND THE ENVIRONMENT AT OOLDEA. 

 Physiography. 



Ooldea is a station, really a construction camp at the time of my 

 visit, on the new railway crossing the continent, and lies about one- 

 third of the distance between Port Augusta on the east and Perth on 



