102 
plants must have included the ancestors of the present day species, 
and probably also other types, the descendants of which have be- 
come extinct. Fossils from portions of our inland South-West and 
Great Southern areas have proved to be remains of Laurineae — 
cinnamon-like plants — which almost certainly lived in a moist 
tropical or sub-tropical climate. Horizons of coal measures, partly 
lost by denudation, are being exposed over increasing areas, and 
these, too, furnish some evidence of ancient floras and environ- 
ments. 
On the living materials (probably the chromosomes in particu- 
lar) of the ancestors of our xerophytic plants, drying climatic con- 
ditions exerted a new set, of stimuli. The development of certain 
characteristics met with repression whilst others, so checked by 
the old order of conditions that they were not able to be evidenced 
at all, slowly made their appearance owing' to either the stimula- 
tion or lack of repression of the new external environmental 
factors. 
In some instances, doubtless, the changes induced in the plants 
were not beneficial. The resultant state of a plant so modified 
would leave it to adjust itself to changing conditions with no 
means for so doing. In other cases, the changes may have been 
inimical, with the result that necessary functions could be carried 
on but imperfectly. Whichever the case, changes being inimical 
or merely immaterial, the effect would be evidenced in a retarded 
rate of reproduction, natural selection ultimately leading* to ex- 
tinction of the plant in regions of appreciable environmental 
change. 
It is certain that in the cases of at least some of the ancestors 
of our xerophytic plants, beneficial alteration of characteristics fol- 
lowed modification of environment, Bufon, advancing the idea of 
variation of species, and Krasmus Darwin, of the inheritance of ac- 
quired characters, first led modern thought towards the great truth 
of progressive evolution. In the light of this truth, we may believe 
that here in this State, through very many hundreds of generations, 
progressive change of structure followed the gradually changing 
water relationship. Such | regressive modification, established in the 
cases of many organisms, is capable of effecting quite drastic struc- 
tural alteration within that portion of geological time to which fos- 
sils give ns reference, and such change is almost certainly responsible 
for mu cli of the specialised anatomy and morphology of our xcro- 
phvtes. 
Some of the plants actually indicate in the individual the pro- 
gressive development of their race. The first leaves of seedlings, 
differing from those of the mature plant, probably resemble the or- 
dinary foliage leaves of remote ancestors. In the case of wattle 
seedlings, it may be noticed that the first leaves are bi pinnate, like 
