684 NOTES ON THE NATIVE FLORA OF N. S. WALES. X., 



My view is that the luxuriant forests on the mountain side 

 are tlie result of a high rainfall induced chietly by the position 

 of such mountains, rather than that the rainfall is a consequence 

 of the presence of the forest. Judging by the vegetation on the 

 higher land towards Bimberi and Coree, it is probable the annual 

 rainfall there reaches 40 inches, and on Bimberi itself, which 

 intercepts clouds from every direction, it possibly amounts to 

 quite 50 inches 



Absence of Trees from Canberra Plains. 



The reason why many thousands of acres of almost level or 

 slightly undulating land should be naturally destitute of trees is 

 difficult to explain. The question is a universal one, and Aus- 

 tralian examples have been much discussed between botanists. 

 The instances are many, and include those from the extensive 

 plains of the interior with a meagre rainfall, whei-e treeless 

 stretches of upwards of fifty miles are not uncommon, to those 

 on the highlands with a rainfall, in exposed situations, as around 

 Kiandra, of sixty inches per annum, and also such spots as those 

 on the upper Dorrigo, where the brush or jungle in places ceases 

 abruptly and forms a fringe on the edge of an open plain. 



My own observations lead me to suggest that the explanation 

 will yet be found in many cases by an examination of the soil, 

 or, in other words, that it is from this source that we shall obtain 

 our best knowledge of the subject, studied in relation to topo- 

 graphy, rainfall, and aspect. Whether the feature is chiefly 

 regulated by the chemical constituents or the physical properties 

 of the soil is difficult to decide, but it is probably in some degree 

 the result of both factors. 



In These Proceedings (1909, p. 3 10), I discussed the question 

 of the absence of trees fiom the Monaro Tableland, and pointed 

 out that, where the hills were composed of siliceous formations, 

 they were more or less tree-clad, while those made up of basic 

 soils were bare, except for some scattered trees of Eucalyptus 

 coriacea and Acacia ruelaHoxylou on a few basalt-summits. 



