ARID PORTIONS OF SOUTH AUSTRALIA. 61 



July 11, the species was flowering and the plants were covered with 

 ants in immense numbers, which appeared to be seeking the nectar of 

 the flowers. The small size of the trees and the large amount of dead 

 wood attested to the very difiicult conditions under which the species 

 was living. So far as the roots could be seen, it was found that many 

 were very near the surface, being often exposed through wind erosion. 

 Although no long horizontal roots were found, it is known that in the 

 mulga and under analogous conditions very long superficial roots are 

 formed. Owing to this fact and to their being of a fairly uniform 

 size, they are used by the aborigines in the making of spear handles. 

 Although the mulga was the only woody perennial found in the sand- 

 hills, a species of "spinifex" or bunch grass appears here and there, and 

 is one of the most characteristic plants of the arid interior. 



On the plain and at a relatively short distance from the base of the 

 sandhills some shrubs and trees are to be found. In places they are 

 relatively abundant and also fairly large. The shrubs are wholly or 

 mainly Eremophila neglecta (plate 5b), about 2 meters high and well 

 clothed with leaves. The trees are of but a single species, "dead 

 finish," Acacia tetragonophylla, which is of wide occurrence in the 

 drier portions of South Australia. The habit of the species is shown 

 in plate 4a and plate 6a. A leading and striking characteristic of the 

 latter species lies in the small size of the phyllodia, which are borne in 

 relatively large numbers, fairly well distributed on the smaller branches. 

 The relative abundance of the species at the base of the sandhills is 

 apparently attributable directly to the comparatively favorable water 

 relations of the place. 



The soil is fairly deep and covered with a sand mulch blown from the 

 neighboring hills. There is a substratum of a white and not especially 

 hard material which has the appearance of travertine limestone and 

 indeed may be that. Whether this prevents the deeper sinking of 

 water or absorbs it, to be yielded again to the plant-roots, was not de- 

 termined. In case the substratum underUes the sandhills as well, 

 which may be the case, a further reason for the relatively abundant 

 vegetation at their base would be found. So far as the substratum is 

 concerned, it was found to crop out along the path to the hills, and in 

 such cases it formed a hard surface quite as in the "caUche," or desert 

 limestone, in the more arid parts of the United States, in southern 

 Algeria, and other dry regions. Moreover, under such conditions it is 

 fairly impervious to water. 



In the habitat at the base of the sandhills there were found a few 

 specimens of the phanerogamous parasite Loranthus exocarpi on 

 Eremophila neglecta. The paucity of this type of vegetation in the 

 vicinity of Oodnadatta forms a striking contrast to the conditions 

 obtaining at Copley, where the mistletoes are very numerous. 



