PLANT HABITS AND HABITATS IN THE ARID 

 PORTIONS OF SOUTH AUSTRALIA. 



INTRODUCTION. ' ' 



, j^,^ ^ Australia, especially South Australia, holds much of interest to the 



'W student of the vegetation of arid regions. ^^^Hiere rain is abundant 



plants compete with one another in a very real way for room in which 

 to hve and for simlight by which they gain energy for various life 

 processes, but_jiL_ragLona...QL.scanty rainfall^ as in portioJia.of Bojith 

 Australia, t here is abundance ofroom and of light. ,H^e the "struggle" 

 is3ssfldaj£d_JzdthjUjej«^^^ is that of the indijodual plant 



withajoaj-i d envirpnment.,flj id-Xmtindividual mth individuah^TwEeh 

 vieweH!lGv^ this standpoint the island continent is seen toTse the field 

 of a vast botanical experiment in which may be observed the reaction 

 of numerous species and innumerable individuals to a physical en- 

 vironment, a leading characteristic of which is a relatively.small water- 

 supply. [M^SO-Ver* Q^Jig toJ!l§_great3ge £Liu^^ (p 

 that JiaHhexfi_el§fi, have plants been, exposed to and influenced by an 

 aiid^nyirpnmejit fgr_a Jonger period of time^J 



The physical background of the Australian plants is in a measure 

 unique. The dry region is very extensive. Some idea of its size can 

 be had by the statement that it has nearly as great an area as all Arabia, 

 and as a matter of fact is larger than all other regions of the kind south 

 of the equator. Living and developing un.der an environment of which 

 the keynote is aridity, the flora of the continent as a whole bears a 

 xerophytic stamp and appears to possess a degree of uniformity which 

 constitutes one of its most marked characteristics. Wherever one 

 goes in Australia, he encounters trees and shrubs with leathery, ever- 

 green leaves. In the better-watered portions the trees are large and 

 numerous and there is an extensive transpiration surface, but in 

 portions less favored in this particular the trees are not large, a shrubby 

 type, of vegetation prevails, and the transpiration siirface is also much 

 restricted in area. Between the two extremes there are innumerable 

 intermediate conditions in which the gradations are quantitative 

 rather than quahtative. When studied in some detail, however, there 

 may be found a bewildering variety of adjustments to the environment, 

 often monotonous perhaps in outward appearance, and which have in 

 a measure the force of belying the generalization just made. 



The physical and biological complexes which enter into om* concep- 

 tion of what constitutes an arid, more especially a desert, region are 

 made up of many features. It is true that they center around the 

 important factor of a small water-supply, but they all should be 

 logically included in any definition of such regions with scanty rainfall. 



