474 PROCEEDINGS OF SECTION D. 



confined to one class of geological formation, it does not follow that this 

 selection is always due to the chemical constituents of the soil — though 

 in a great many instances such is the case — but may be regulated by its 

 physical features, such as adaptability to hold moisture, or otherwise. 

 Other factors, including rainfall and aspect, may assist in governing the 

 question of distribution in such cases. There are many plants which 

 thrive on hillsides but cease as soon as the valley is reached, although the 

 soil in the latter may be produced from the weathering of the adjacent 

 hills. Eucalyptus h'emastoma Sm. (white or brittle gum) is one of these ; 

 and it seems remarkable that a large tree should prefer a rocky hill to 

 an alluvial flat. Many plants, of course, which flourish on the flats do 

 not occur on the surrounding hills, and the question of suitable drainage 

 appears to be one of the factors in regulating these preferences. For 

 these reasons, the chemical analysis of a soil may not of itself be sufficient 

 to indicate what plants will be best nourished in the locality whence 

 such soil is obtained. 



T. W. Woodhead, F.L.S., (9) in writing on the Ecology of Woodland 

 Plants in the neighborhood of Huddersfield, states : — " The present 

 study indicates that, in this district, the physical properties of the soil 

 and accompanying conditions play a more important part in determining 

 the character of plant associations and the distribution of species than 

 the chemical composition of the soil." 



The flora of New South Wales may be divided for purposes of general 

 study into four divisions, viz. : — The coastal area, the mountain area, 

 the western slopes, and the interior. These divisions are illustrated 

 on the accompanying map, and, although shown by fairly straight lines, 

 the actual boundaries follow a most sinuous course, according to the 

 contours of some of the mountain gorges and intervening elevations, 

 which it is difficult to trace with exactness. The Great Dividing Range 

 plays an important part in regulating the growth and distribution of 

 the vegetation. The amount of moisture along the coastal area is 

 greater than that of the interior, consequently the two floras are quite 

 distinct, while a third may be found along the highest part of the 

 mountains as the result of climatic influence. Owing to the great ex- 

 tent of sloping country on the west, a fourth flora is found connecting 

 the interior with the mountains. 



The mean annual rainfall of the coastal area south of Sydney is 

 about 41in., while to the north of Sydney it approximates 51 in., though 

 these averages are exceeded at many points along the seashore. The 

 average annual rainfall of the mountain area is about 34in., of the 

 western slopes about 26-27in., and of the interior about 13-14in., with 

 less than lOin. at Broken Hill. 



The physiographic features of the State in relation to their influence 

 on the flora may be briefly described as follows : — The main range forms 

 a backbone, traversing from north to south at an average distance of 

 about 80 miles from the coastline on the east, and some 500 miles from 

 the central portion of the Darling River on the west. On the eastern, 

 or coastal, area the geological formation over a fairly considerable ex- 

 tent is sedimentary, consisting in many places of sandstones and shales, 

 the latter of which are somewhat readily removed by the action of water 



