Cockayne. — Plants of Chatham Island. 305 



abundant, Crantzia lineata and Pratia arenaria, are considered 

 by Chatham Island sheep-farmers" most valuable pasture 

 plants ; and there seems little doubt that these two plants at 

 any rate, owing to former plant adversaries having been re- 

 moved, partly through changed edaphic conditions and partly 

 through close grazing by animals, have become very much 

 more abundant in Chatham Island generally than was formerly 

 the case — helped, of course, by the great vegetative increase 

 of their stems rendering them safe from the attacks of sheep. 

 But if a plant be isolated and there is no other food for the 

 grazing animals it may not be able to hold its own. Thus 

 Poa chathamica, notwithstanding its strong wire-like rhizome, 

 cannot resist close grazing on the tableland bogs, where no 

 other food is present for the hungry animals, and it may be 

 eradicated for a time. 



Besides domestic animals, certain European birds have 

 been brought over to the island, and others, strange to say, 

 amongst which are the sparrow and blackbird, are said to 

 have made their way from New Zealand unaided. Such 

 birds play a much more prominent part with regard to the 

 introduced than to the indigenous vegetation, doing a great 

 deal of damage to the crops and gardens of the farmer. They 

 also carry and distribute the seeds of both native and intro- 

 duced plants ; in this case, as pointed out before, doing the 

 work of the former indigenous birds, which now for the most 

 part have become very limited in number. Perhaps the 

 greatest work such birds are performing is that of spreading 

 the blackberry all over the island, but this matter concerns 

 the next section. 



As for the effect of introduced insects, I procured no infor- 

 mation ; probably the hive bee plays an important part in 

 fertilising certain of the introduced plants, and so causing 

 their spread. 



Effect of Introduced Plants.! 



With regard to the influence of introduced plants on the 

 vegetation of Chatham Island I can say little, the time at my 

 disposal not permitting me to collect examples, or even make 

 a list of the species. Mr. T. Kirk published a list of those 

 introduced plants which Travers collected (35), but it contains 

 only twenty-eight species. Probably there were even then 



* Mr. E. R. Chudleigh, for instance. 



f On the importance of this subject Mr. Hemsley, speaking of the 

 work of the late Mr. T. Kirk (38), writes in Nature (27): " He "— Mr. 

 Kirk — "has put on record facts connected with the introduction and 

 colonisation of exotic plants in New Zealand that positively throw a new 

 light and suggest new ideas on the present distribution of plants in 

 cultivated countries generally." 



20 



