EFFECT OF SETTLEMENT UPON INDIGENOUS VEGETATION. 229 
The theory that insulated floras are less able to resist the influx 
of foreign plants is supported by the fact that only in the Neil- 
gherrie Mountains in India have Australian plants been able to 
compete with others to any extent. It is, I believe, considered 
that that part of India long existed as an insular region. There- 
fore we see that the Australian flora, which though isolated, had 
a large range, is able to get an advantage over the Neilgherrie 
flora which was for so long developed in a small centrum. | 
One cause of the power of spreading of what are commonly 
called weeds, is that they are usually plants with inconspicuous 
flowers, and as such are generally self-fertilised and so can get 
along without specialised insects to fertilise them. It is manifest 
that in a new country where the local insect fauna is being 
destroyed to some extent, the plants which have not to depend on 
insects for fertilisation will be the more likely to win. And even 
cross-fertilised plants seem to manage sometimes to find insects to 
perform that office for them. Moseley points out an instance in 
the following passage: ‘“‘The orange, lemon and lime, which grow 
wild all over Tahiti do not appear to deteriorate at all in quality 
or quantity of fruit, although in the ferine condition. The fruit 
almost appears finer for running wild. . . . . Some native 
insect must have adapted itself completely to the blossoms of the 
orange tribe as fertiliser, so abundant is the fruit."* The same 
is the case in Australia, for although the orange does not seem 
to grow wild to any extent, lemons have made themselves at home 
in the Illawarra District. The flowers of the lemon and the native 
plant Synoum glandulosum are much alike in structure, and it 
may be that the same insect or insects fertilise them. These 
plants would be on equal terms in this respect, but the lemon from 
its wide cultivation has gained a power of bearing diverse con- 
ditions which gives it a better footing, I may remark that 
Synoum is a common plant in Illawarra. 
Among wind-fertilised plants are the grasses. The introduced 
species so far are not beating the natives. They are equal as far 
* Notes of a Naturalist on the Challenger, p. 524. 
