556 



reaclieii a more advanced phase as one passes east for 15 to 

 20 miles, where mallee is found to cover almost all the sand 

 ridge?. On the other hand, nearer the plains, the presumably 

 younger sandliills are almost or quite without mallee and are 

 occujDied by Acacias. 



To summarize, excluding the salt lake witli its highly 

 saline S23ecial conditions, one can recognize probably four types 

 of vegetation: — (a) The NuUarbor Plain, with its open .com- 

 munities of Kocliia sedifolici or Atriple.r spp. ; (h ) the sand- 

 hill ridges commencing with Leptos'permum, JaevigaUun and 

 Acacia Iif/oph?/lla, etc., and culminating in an open mallee 

 community ; (cj the sandhill hollows with sandy soil culmin- 

 ating in open forest of Casnarina lejjidophloia: and lastly, 

 (d) the hollows with firmer soil which appear to reach a climax 

 in the community of MjiopGniin plat year piim and Hetero- 

 dendroii ohi folium. These last two are very closely allied and 

 all sorts of transitions with intermediate conditions can be 

 noted. 



The donga communities represent attempts stopped by 

 conditions to develop upon the open plain the vegetation char- 

 acteristic of one cr other of these last two types. 



Flora. 



A list of the flora so far as v/e have collected it is given 

 belovc (Appendix). This has been enlarged by the inclusion 

 of thirty species recorded or collected by Black from the 

 Ooldea district, but not seen by us. The total number of 

 species amounts to 188. 



In this, list we have given the habitats of the, plants 

 dividing the district into six main divisions, viz., the Nullarbor 

 Plain, the dongas on the plain, the sand ridges, the sand flats 

 between the. ridges, the Soak, and the salt lake. From such 

 a list the several plant communities recognized by us can easily 

 be seen to have their characteristic floras. iSTecessarily the 

 classification is somewhat arbitrary, special difficulty being 

 found in deciding whether a plant growing at the edge of the 

 Nullarbor Plain properly belongs to the plain flora or to that 

 of the sandhill areas. Nevertheless, it becomes clear that, as 

 we have stated above, the donga flora has more resemblance to 

 that of the sandhill country than to that of the plain. 



Secondlv, it will be seen that in the sandhill area the floras 

 of ridges and of flats are strikingly distinct, sufficiently so to 

 recognize them as different associations. Again, however, it has 

 not been possible to distinguish in tabular form between those 

 flatvs with a deep sandy or loamy soil, and those in which the 

 underlvinor limestone comes near to the surface. These last 

 are recognized as being inliers of the plain association that 



