47 
The Adaptation of Plants to Environ- 
ment. 
By A. MORRISON, L.R.C.P. & S. (Edin.) 
(Read before the Society on the 14th September, 1909.) 
As the land composing the State of Western Australia has 
been for many ages undisturbed by upheavals of a geological 
nature, the soil and climate must have varied very little during 
all that time, so that at the present day the conditions of existence 
for organic beings may be taken to be similar to those prevailing 
many thousand years ago. Through all this time successive 
generations of plants have been accommodating themselves to 
the conditions surrounding them, with the alternative that, if 
they could not so adapt themselves, they would suffer extinction. 
Individual plants that have for any reason been able to with- 
' stand particular trying conditions better than their companions 
have in consequence of this survived, and their descendants, 
through their possession of those qualities, have continued on 
their course, A certain amount of modification of structure will 
accompany, if it be not the cause of, this power of resistance, and 
when further modifications of the same kind arise, or others 
equally favorable, or other characteristics are introduced by 
crossing with different forms, the plant may thus, by a process 
of natural selection, be so much altered from its original form 
as to constitute a distinct species. Long continued drought, for 
example, would impose such a test of the endurance of plants ; 
and as a matter of fact, drought, periodic or constant, is the 
most prominent and characteristic feature of the environment of 
plants in Western Australia. In only a few other regions on the 
earth’s surface is aridity of climate so pronounced as in some parts 
of Australia, and yet the driest parts of its area are furnished with 
plants able to live through it and propagate their kind. We are 
thus led to infer that our native plants must b?, particularly well 
adapted to droughty conditions, while the duration of this dry 
environment and of the resulting structural modifications, seems 
to suggest the idea of fixity of the forms now existing, seeing that 
a long-continued succession of similar seasonal cycles, with little 
disturbance of soil conditions, must in the course of time have 
brought each form of plant to a state of perfection in its adaptation 
to this unvarying environment. 
According to Weismann and others, acquired characters can- 
not be inherited, the germ plasm being continued unaltered in struc- 
