ARID PORTIONS OF SOUTH AUSTRALIA. 107 



cially by the unimportant washes are scattering specimens oi Acacia sentis. 

 Strictly speaking, the latter species belongs rather to the valley than to 

 the hill flora. 



Vegetation of the Washes. 



It has been remarked that at Quom there is frequently no sharp 

 distinction between valley, hill, and stream-plain, but that in places 

 the flora of the three may merge, even if in others they are quite sepa- 

 rate. This is possibly less true of the vegetation of the streamways 

 than of the other formations. The characteristic species of the streams 

 is Eucalyptus leucoxylon var. pauperita. This is strictly limited to 

 streams. It is a good-sized tree, becoming about 7.6 meters in cir- 

 cumference (plate 30b). By the low banks along the washes, which 

 are dry most of the year, are other species which also rarely, or never, 

 occur elsewhere. For example. Acacia pycnantha forms a small thicket 

 by the wash near the Mount Brown road about 3 miles southwest of 

 Quorn (plate 30a), but there are no other species of woody plants here. 



Root Chabacteks. 



Some observations were made on the root-habits of the mallees. 

 Eucalyptus oleosa and E. odorata, and of the large gum, E. leucoxylon 

 var, pauperita, of the washes. The former was especially studied in 

 the small mallee community about 3 nules north of Quorn. Here a 

 narrow wash runs by the edge of the scrub, where the soil is fairly 

 coarse and where rock underlies it to a depth of about a meter; it was 

 found that the tap-root was poorly developed, but that there were 

 niunerous radiating superficial roots. In a typical specimen there are 

 about 12 main laterals of this character which are placed 23 to 45 cm. 

 beneath the surface (plate 31a) . Many roots, about 2 mm. in diameter, 

 arise near the bases of the large laterals and go directly down. 



At another place, by the Port Augusta road and about 4 miles 

 west of Quom, a fairly deep wash also exposes roots of mallees growing 

 along its side. Here the wash is about 2 meters deep and, although 

 there does not appear to be rock to limit possible root penetration, all 

 of the species had the superficial type of roots well developed. In 

 one instance a root was traced 11 meters from the base of the tree, and 

 at a distance of 7 meters it had a diameter of 2.5 cm- In another case, 

 after having extended 2 meters from the tree close to the surface of 

 the ground, the horizontal root sent a branch straight down. This 

 was about three times the diameter of the parent root and was traced 

 to a depth of 2 meters. The horizontal roots were found to lie usually 

 within 20 cm. of the surface of the ground. 



Owing to its usual position in the bottom of the washes, the roots of 

 the gums here are rarely much exposed, but it is usual for several 

 prominent roots to take their origin close to the surface of the ground; 

 in one instance it was found that such roots may extend for a long 

 distance near the surface. By the streamway, for example, about a 



