272 Transactions. — Botany . 



success against species that bave 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 buttercups, 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 Microlcuna 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 

 reason 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 



