501 ISLAND LIFE. 



Fully one-third of the exclusively Australo-New Zealand 

 species belong to the two great orders of the sedges and 

 the grasses ; and there can be no doubt that these have 

 great facilities for dispersion in a variety of ways. Their 

 seeds, often enveloped in chaffy glumes, would be carried 

 long distances by storms of wind, and even if finally dropped 

 into the sea would have so much less distance to reach the 

 land by means of surface currents; and Mr. Darwin's 

 experiments show that even cultivated oats germinated 

 after 100 days' immersion in sea- water. Others 

 have hispid awns by which they would become attached 

 to the feathers of birds, and there is no doubt this is an 

 effective mode of dispersal. But a still more important 

 point is, probably, that these plants are generally, if not 

 always, wind-fertilised, and are thus independent of any 

 pecidiar insects, which might be wanting in the new 

 country. 



Why Easily-Dispersed Plants have often Restricted Ranges, 

 — This last consideration throws light on a very curious 

 point, which has been noted as a difficulty by Sir Joseph 

 Hooker, that plants which have most clear and decided 

 powers of dispersal by wind or other means, have w.t 

 generally the widest specific range ; and he instances the 

 small number of Compositae common to New Zealand and 

 Australia. But in all these cases it will, I think, be found 

 that although the sjJecies have not a wide range the genera 

 often have. In New Zealand, for instance, the Composita? 

 are very abundant, there being no less than 167 species, 

 almost all belonging to Australian genera, yet only about 

 one-sixteenth of the whole are identical in the two 

 countries. The explanation of this is not difficult. Owing 

 to their great powers of dispersal, the Australian Compositae 

 reached New Zealand at a very remote epoch, and such as 

 were adapted to the climate and the means of fertilisation 

 established themselves ; but being highly organised plants 

 with great flexibility of organisation, they soon became 

 modified in accordance with the new conditions, producing 

 many special forms in different localities ; and these, spread- 

 ing widely, soon took possession of all suitable stations. 

 Henceforth immigrants from Australia had to compete 



