272 Transactions.— Botany. 
success against species that have from time immemorial occupied the cultiva- 
tions of man, and whose best adapted varieties have been rigorously selected. 
The introduced weeds flourish and multiply because they have an environ- 
ment suited to them, and to which they have been modified; the native 
ones fail because the conditions have become altogether different to those 
they had been accustomed to. 
Similarly it was to be expected that foreign plants would in some degree 
displace the indigenous ones in districts grazed over but not actually culti- 
vated. Many native species will not bear repeated cropping, and soon 
decrease in numbers when cattle or sheep are brought in. Their places 
. will, therefore, be taken by plants that are indifferent to this, or escape by 
reason of being unpalatable. It hardly needs pointing out that many of our 
introduced species are in this category. The common thistle, for instance, 
is protected by its prickly leaves; the docks and buttereups, and many 
labiate plants, are rejected by stock, save when food is scarce, on account 
of their unpleasant taste ; while most grasses and some leguminous plants 
may be eaten down repeatedly without suffering much permanent injury. 
It is obvious that these species would have a good chance of spreading if 
introduced into a district where sheep and cattle are numerous. At the 
same time it must be remembered that any native plants possessing similar 
advantages would also increase ; and in many cases this has actually taken 
place. The spread of such indigenous plants as Poa australis and Discaria 
in the river valleys in the interior of Nelson and Canterbury; of Cassinia on 
the shores of Cook Straits; and of some grasses (as Danthonia semiannu- 
laris and Microlena stipoides) in Auckland, are well-known examples, and it 
would be easy to enumerate more. 
But although we may safely credit the changed conditions of plant-life 
with being a powerful reason for the spread of naturalized plants in New 
Zealand, it is impossible to consider it as the sole explanation. For we 
find that not a few species have penetrated into localities where cultivation 
and cattle are alike unknown, and where man himself is a rare visitant ; 
where, in fact, the conditions are still unchanged. This is the most inter- 
esting part of the subject, for it proves conclusively, as remarked by Mr. 
Darwin, that the indigenous plants of any district are not necessarily those 
best suited for it. In most cases it is impossible to assign any obvious 
Teason for the fact that these intruders should be able to thrust on one side 
the native vegetation; but it is significant that all, or nearly all, are 
common and widely distributed in their native countries; in short, are pre- 
dominant species; and that they have followed almost everywhere the foot- 
steps of man, being as extensively naturalized in many other countries as 
in New Zealand. We may, therefore, suppose that by long-continued 
