NATIVE FLORA OF TROPICAL QUEENSLAND. 399 



C. Cunninghamiana (River Oak) was noticed on many of 

 the large streams from Kuranda to Alma-den, including the 

 head waters of the Walsh River, a tributary of the Mitchell, 

 but was not seen on the lower Gilbert or lower Flinders. 

 Although this species ranges from North Queensland 

 southerly to the Murrumbidgee River, and occurs on fresh 

 water streams on both sides of the Main Divide, it appears 

 to have limitations in regard to its powers of resisting 

 extremes of cold and salinity. Thus, although it occurs on 

 the upper portions of all the main western rivers of New 

 South Wales from the Murrumbidgee northwards, it has not 

 been recorded from Victoria, nor does it extend down the 

 rivers to the Murray, as though it prefers the swiftly run- 

 ning to the sluggish streams. It is rarely found at eleva- 

 tions exceeding 3,000 feet above sea level. It is of interest 

 to note that its distribution in North Queensland seems to 

 be regulated by the same factors which govern its occur- 

 rence in the south, and it appears throughout to avoid the 

 lower portions of the western streams. As previously 

 suggested, its inability to descend the rivers to the sluggish 

 portions may be owing to the presence there of saline con- 

 ditions which often prevail in times of drought, and which 

 this species always shuns. 1 



In 1845 Leichhardt noted its absence from the lower 

 portions of the Gilbert, Norman, Flinders, Leichhardt and 

 Albert Rivers, and when on the Nicholson, near the western 

 border of Queensland, he wrote: — "We crossed a creek in 

 which we recognised a Casuarina, which tree we had not 

 seen since we left the Mitchell." 2 He does not mention 

 what species of Casuarina was growing on the Nicholson. 



The River Oak affords a splendid object lesson in the 

 limitations which may sometimes attend the distribution 



1 Notes on the Botany of the Interior of New South Wales," Part V. 

 By E. H. Cambage. Proc. Linn. Soc. N.S. Wales, Vol. xxvi, (1901) p. 635. 



2 Journal of an Overland Expedition in Australia, p. 368. 



