62 PLANT HABITS AND HABITATS IN THE 



Although there is thus seen to be a comparatively abundant peren- 

 nial flora at and near the sandhills, yet the largest number of woody 

 plants about Oodnadatta, especially the largest number of trees, is 

 to be found in water channels of whatever kind, either Neales River 

 or washes at the bases of the flat-topped hills. As viewed from the 

 vantage-point of the upper or even the lower plain (plate 5c), the 

 Neales River bottoms has a considerable tree population, and par- 

 ticularly a large number of shrubs. The present-day shrub and tree 

 population of the flood-plain of the river can not be taken as indicative 

 of what must have been the condition in earlier times. The inhabitants 

 of the nearby town have actively removed all trees large enough to 

 supply fuel. The shrubs, however, have probably very largely escaped 

 such inroads. The same remark would also apply to the neighboring 

 washes, wh^re the water relations are suitable for some tree-growth. 



Of the species now to be found on the flood-plain of Neales River, 

 the most conspicuous are Eucalyptus rostrata (plate 4c) and species 

 of Acacia, among which are A. cambadgei, A. tetragonophylla, and A. 

 stenophylla. There are also several species of saltbushes, several 

 shrubs whose identity was not determined, and some annuals. Of the 

 trees. Acacia cambadgei is possibly the most numerous. This is the 

 "stinking" acacia, or "gidya," the name given it by the aborigines, 

 which is said to refer to an edible (for aborigines!) larva which is to be 

 found beneath the bark. The tree attains a height of 10 meters or 

 more and has a compact habit of growth. Like the other species of 

 Acacia growing in the far north, true leaves are not present on the 

 mature plant, but their place is taken by phyllodia. In the case of the 

 gidya the phyllodia are fairly large as well as abundant, so that a 

 distinctly leafy effect is produced (plate 6a) and the shade cast is 

 dense — a rare occurrence in desert plants. 



A. tetragonophylla is also a small tree, but with a foliar habit quite 

 different from the species last mentioned. Its phyllodia are needle- 

 form, 8 to 28 mm. in length, and may occur in groups of a few each. 

 They fall away fairly easily and the ground beneath the trees is usually 

 thickly covered with them. It appears probable that the shedding 

 of the phyllodia should be considered a very effective means of re- 

 ducing the evaporation surface and hence of cutting down excessive loss 

 of water during especially severe drought. The foliar habit of A. 

 stenophylla is unlike that of either of the species above mentioned. 

 The species is a small tree or a large shrub at Oodnadatta and true 

 leaves are formed on young shoots, although they are soon cast off, 

 phyllodia taking their place (plate 6b). The phyllodia are various 

 as to form and size, but in general they are long, narrow, and even 

 linear in the extreme form. In the portions of a plant which are sub- 

 jected to the most intense illumination the phyllodia assume an up- 

 right position, but where shaded they are pendant. 



