GUPPY ON PACIFIC CONTINENT 325 



that the story of plant distribution in the Pacific is bound 

 up with the successive stages of decreasing activity in the 

 dispersing agencies. He thinks that the area of active dis- 

 persion, as illustrated by the non-endemic genera of plants, 

 at first comprised the whole of the tropical Pacific.* After- 

 wards it was limited to the southern Pacific, and finally to the 

 western Pacific only. The birds that carried seeds all over this 

 ocean became more and more restricted in their range, pro- 

 bably, as Mr. Guppy suggests, on account of increasing 

 diversity of climatic conditions. The plants of necessity re- 

 sponded to the ever narrowing conditions of bird-life in this 

 ocean, the differentiation of the plant and bird taking place 

 together. 



Mr. Guppy dislikes the idea of hypothetical alterations in 

 the present relations of land and water, and yet what an 

 amount of hypothesis he has to resort to in his endeavour to 

 explain the theory which he is so anxious to support ! There 

 is not a scrap of evidence for the belief that dispersing 

 agencies have practically ceased at the present time, nor that 

 the migrations of birds have diminished. On the contrary, 

 ornithologists have done their utmost to trace the origin of 

 all bird migrations to the gradually increasing diversity of 

 climatic conditions during the Tertiary Era, which they sup- 

 pose to have culminated in the Glacial Epoch. Although we 

 have little evidence for such a belief, it seems a reasonable 

 supposition. But what can be said in favour of Mr. Guppy'a 

 theory, that, owing to the increasing diversity of climatic con- 

 ditions, the seed-carrying birds have become more restricted, 

 that is to say, less migratory ? 



A careful perusal of Mr. Guppy's work must make it evident 

 to anyone, that, although plants have far greater facilities for 

 accidental transport, and have in many cases actually been 

 thus conveyed from one land surface to another, they agree 

 on the whole perfectly with animals, in so far as the Pacific 

 islands are largely tenanted by very ancient types. If we adopt 

 the theory of accidental dispersal for the origin of the Pacific 

 island flora, we must apparently assume that the means of 

 occasional conveyance were far more efficient in former times 



* Guppy, H. B., "A Naturalist in the Pacific," II., pp. 519520. 



