EFFECT OF SETTLEMENT UPON INDIGENOUS VEGETATION. 223 
All the foregoing tends to show how direct or indirect modi- 
fication of the fauna of a country must react beneficially or in- 
juriously on the flora. 
As another example of how these causes react on a flora the 
following may be of interest: ‘“ We know for example that 
drainage will affect the distribution of the butterfly-orchis, because 
it affects the insects which alone can fertilise this peculiar kind 
of flower.”* Again: “ And it isa remarkable fact that the smoke 
and chemical odours which surcharge the atmosphere of such of 
our large towns as Manchester, Leeds, and Derby, by causing 
certain kinds of insects to keep away, have indirectly but posi- 
tively made it impossible for numbers of wild plants, formerly 
included in local floras, to perpetuate themselves now.” 
ivision. ULV. 
Introduction of a new flora, and consequent modification of the 
indigenous flora. 
This is a very important source of modification of the vegetation 
of any new country. It may be considered under the following 
heads :— 
(a) Manner of introduction and spread. 
(6) Action on local flora. 
(c) Introduction of indigenous plants to new localities. 
(dz) The plants introduced. 
(a) Manner of introduction and spread. 
The plants which have become naturalised in Australia, natur- 
ally come under two headings, viz., those purposely introduced 
for use, ornament or sentiment, and those which accidentally 
found their way here. 
Of those introduced for use or for ornamental purposes, a large 
number do not spread to any extent: they are children of civili- 
sation and show no tendency to become feral. Many hardy 
annual garden flowers come up self-sown in gardens year after 
* J. E. Taylor—Flowers, their origin, shapes, etc., p. 19. 
