CHAP. LXXIII SHRUB-STEPPE 281 



of Australia, where drought prevails because the trade-wind has given 

 up its moisture to the coastal mountains long before reaching these parts. 

 These bushlands are about 3 or 4 metres in stature, and consist of entangled, 

 often impenetrable shrubs, which are evergreen, though they are dirty 

 green or brownish-green in tint. True thorny shrubs are not very common, 

 though the leaves are often very narrow or divided with many stiff linear 

 segments that terminate in spine-like points. Plants belonging to the 

 ericoid or pinoid form are general, and especially so among Proteaceae ; 

 other plants, namely, species of Acacia and Eucalyptus, have phyllodes 

 or leaves with their surfaces vertical ; yet broad, stiff, rustling leaves 

 also occur. Between the shrubs the ground is often bare, as grass and 

 herbs are extremely scanty, or it may be clothed with a dense undergrowth 

 of bushes. Many species, which vary with the district, compose this for- 

 bidding vegetation, for which no economic use has yet been found. The most 

 notable families represented here are Proteaceae, Myrtaceae (including 

 Eucalyptus, Melaleuca, Leptospermum, and others), Epacridaceae, 

 Mimoseae (with Acacia), Myoporaceae, and others. There are special 

 types (' associations ' or 'sub-formations') of scrub, for instance : 



Mallee-scrub is largely composed of Eucalyptus-shrubs, whose stature 

 is, on the average, nearly that of man. In dreary monotony this 

 stretches like an unending sea of shrubs over the flat arid table-land, 

 with the bare, yellow or rust-coloured soil showing between the confused 

 maze of branches. 



Mulga-scrub is mainly composed of thorny acacias, which form impene- 

 trable associations where they grow close together. 



Brigalow-scrub is largely formed by Acacia harpophylla. 1 



Scott-Elliot 2 remarks that Acacia shrub-lands ' surround the deserts 

 in tropical and subtropical countries '. He describes how the vegetation 

 changes when one steps from the ' ordinary tropical monsoon wood ' 

 into the desert, how it passes over into ' isolated pioneer thorn shrubs 

 or small trees dotted over the ground ' ; and how ' these isolated pioneers 

 or scouts are almost invariably Acacias '. Such a ' transitional Acacia- 

 and thorn-scrub region with a long dry season ' is encountered in many 

 parts of Africa, Australia, and South and North America. This type of 

 vegetation demonstrates the difficulty of distinguishing between tropical 

 thorny bushland and subtropical shrub-steppe. 



CHAPTER LXXIV. GRASS-STEPPE 



TYPICAL steppes in the narrower sense of the term are grass-steppes, 

 which occur in the form of extensive treeless plains clothed with grasses 

 and other perennial herbs : 



In the Old World South Russia, Hungary, Central Asia as steppes. 

 In North America as prairies. 

 In South America as pampas. 

 The vegetation is xerophilous in character, and does not form a dense, 



1 Michaelsen und Hartmeyer, 1907. Recently Diels (1906) has issued an excel- 

 lent work dealing with South-West Australia. 2 Scott-Elliot, 1905. 



