218 A. G. HAMILTON. 
suffer and the plants be correspondingly benefited or injured. 
That this is no far-fetched theory, Darwin’s well-known instance 
of the influence of cats on the yield of red clover shows.* 
There can be no doubt that the extermination of the aboriginals, 
the native dog and other enemies of the Poephagous marsupials 
has resulted in an enormous increase of the latter, and that plants 
have been affected thereby to no small extent. In the same way 
the extinction of certain Meliphagide and honey-eating paraquets, 
would cause trees habitually fertilised by them to become more or | 
less barren. Many of our eucalypts are fertilised by paraquets. 
Indeed some naturalists have gone so far as to express an opinion 
that certain puzzling species of this genus which systematists find 
hard to place or even to separate, are really hybrids made by birds 
of this kind in their search for honey. Be this as it may, there 
is no doubt that any such alterations in a flora would be brought 
about with extreme slowness, although the extinction of animals 
and insects, or their increase, might have taken place at a very 
rapid rate. Furthermore it would be a change which would be 
difficult to detect, and there can be no doubt but that it would be 
modified by the action of the principle of Natural Selection. 
For when we consider the vast amount of variation which takes 
place in every species (on this subject vide Wallace’s Darwinism, 
Chap. 111.) it is hard to avoid the conclusion that some individuals 
would vary in a direction giving them a better chance of survival 
under the changed conditions, and slowly but surely such indi- 
viduals would establish themselves, first as a dominant race, and 
at length a species fitted for the new opening in the organic net- 
work. 
Darwin gives an instance “Showing how complex and unex- 
pected are the checks and relations between organic beings which 
have to struggle together in the same country. . . . . In 
Staffordshire, on the estate of a relation, where I had ample means 
of investigation, there was a large and extremely barren heath, 
which had never been touched by the hand of man; but several 
* Origin of Species, 6th Edit., p. 57. 
