ii6 Sutton, A Sketch of the Keilor Plains Flora. [vj"^x 



Nat. 

 XXIII. 



the continual grazing of animals have each in varying degrees 

 been responsible for the low, sparse plant cover we see 

 to-day. The grass-land is, then, the "reflex " of the sum total of 

 these comparatively severe conditions which constitute the 

 " habitat." 



While the conditions are by no means so extreme as those 

 responsible for certain grass-lands in other parts of the world 

 known as grass-steppes, the principal examples of which are 

 the steppes of Russia, the prairies of North America, and the 

 veldt of South Africa, they have yet been sufificiently pro- 

 nounced to have impressed on the vegetation of the basalt 

 plains many of the features of grass-steppes. Thus, the short 

 plant cover of dominant grasses, with herbs and stunted under- 

 shrubs, is mainly xerophytic ; it does not form a close carpet 

 as in a meadow, the bare ground being constantly visible, and 

 it fades in summer. Many of its grasses are tufted and have 

 rolled leaves, and composites (i6 per cent.) and annuals (12 per 

 cent.) form large proportions of its constituent species. While 

 bulbous and tuberous plants and perennials with deep tap- 

 roots or thick root-stocks are present, they are, howev'er, not 

 prominent. Thus the formation, if it may not be called a grass- 

 steppe, is at least a grass-land with steppe-like characters, though 

 Diels would possibly regard it as dry pasture or " trift " in his 

 classification. 



Further, it is agreed that all undisturbed laud surfaces 

 are destined, sooner or later, to pass, either indirectly by 

 way of scrub-land or directly, into forest. It is also laid 

 down that a rainfall of at least 20 inches in about 100 days is 

 required to favour forest growth. Although over wide stretches 

 of the basalt plains trees are absent, and from all appearances, 

 or want of them, have never e.xisted, it is quite obvious that 

 the change from grass-land to forest has been steadily but very 

 slowly taking place. In the southern portion, where the 

 necessary condition as regards rainfall just exists, this change 

 is not at once visible, though individual trees and groups of 

 them are to be found widely scattered. It is in the northern 

 part of the area, with a higher rainfall, that the change is more 

 obvious, partly in the advance of trees up the branches of the 

 main water-courses and over the edges of the latter on to the 

 plain, l)ut princii)ally at the outskirts, by the invasion of trees 

 from the neighbouring forest formations. 



The surface of the basalt is comparatively new — it is assimied 

 that it is newer than those adjoining — but ])r()bably not so new 

 that it would not at the present time have supported forest if 

 conditions had been more favourable. The transition, so far 

 as it has gone, appears to have been direct, .\dverse conditions 

 have delayed it, and it may be concluded that ultimately, il 



