58 PLANT HABITS AND HABITATS IN THE 



Tate, there are 55 species of grasses, mainly annual, which are to be 

 found also in northern South Australia. These for the most part are 

 to be seen only after rains, possibly mainly those of summer. 



VEGETATION OF THE LAKE EYRE BASIN. 



As one enters the Lake Eyre region by the railway, the general im- 

 pression is had, which becomes stronger upon further acquaintance 

 with the region, that the total amount of perennial vegetation has 

 suddenly become less, despite the large halophytic population. More- 

 over, the larger elements of the vegetation are more and more re- 

 stricted to the water-courses and a relatively small amount is to be 

 seen venturing away from them. The differences noted are possibly 

 most marked with the tree flora. Clearly such a generalized statement 

 is difficult, if not impossible, to demonstrate. One would, of course, 

 expect a falling off in the amount of vegetation in a region having only 

 5 inches as opposed to one having nearly 9 inches — ^for example, 

 that about Copley. But the point I wish to make is that the differ- 

 ence is greater than the difference in the recorded rainfall would lead 

 one to expect. To illustrate the idea crudely, we may suppose the 

 amount of vegetation and the amount of rainfall to be represented in a 

 figure by two curves. The curve representing the amount of vegeta- 

 tion is assumed to decUne parallel to that representing a decrease in the 

 precipitation. However, with the decreased rainfall there comes a 

 rapid increase of other climatic factors makiag for aridity, and espe- 

 cially there occurs, in the Lake Eyre region, a relatively large proportion 

 of non-effective precipitation. We therefore get a diverging of the 

 vegetation-rainfall curves which at the last is very sharp. The sudden 

 falling of the vegetation curve I believe to be directly related to the 

 large percentage of non-effectivfe rainfall, although with it there 

 naturally must be associated an intensification of other environmental 

 physical factors working toward the same end. In other words, the 

 effect is as if in place of contrasting regions having about 5 and 9 inches 

 of rain, we are contrasting regions whose effective rainfall may be said 

 to be about 3 and possibly 8 inches. 



VEGETATION AT OODNADATTA. 

 A general idea of the amount of the perennial vegetation in the vicin- 

 ity of Oodnadatta may be had by ascending O'Halloran's Mount, 

 which is about 4 miles to the north of the village (plate 1a). This 

 low hill is evidently a detached portion of the upper plain and it com- 

 mands a very good view of the desert. As one surveys the surrounding 

 country he is at first struck with the paucity or rather with the want of 

 plant covering. In every direction the wide-spreading plains and 

 flat-topped hills appear quite barren. The gibbers glisten like polished 

 mirrors in the sun, but otherwise a monotonous reddish-brown color 

 prevails. There are thus apparently no plants to enliven the scene. 



