CH. II] INTO NEW AREAS 17 



dine, or couch-grass, will need no information as to the efficiency 

 of this method. Tithonia diversifolia (Compositae), which has no 

 pappus, and is dispersed almost entirely by vegetative methods, 

 has spread in Ceylon as widely and almost as rapidly as Lantana, 

 which is bird-carried. Elodea in the waters of western Europe 

 was a similar case, for only the female plant is known there. 

 Vegetative reproduction cannot carry a plant very far at one 

 operation, but it is probable that to travel far, unless into virgin 

 soil, is really rather a handicap; and the young plant has the 

 enormous advantage of connection with the parent, or in any 

 case of a good supply of food with which to commence life. 



Several other researches have been carried out in recent years 

 upon the actual transport of seeds and fruits. Of these by far 

 the most important are those of Guppy upon the stocking with 

 plants of islands of the Pacific and Atlantic Oceans (44, 47). 

 He discusses in detail the agencies that can effect distribution, 

 pointing out that the currents only take a comparatively minor 

 part in it. About 90 per cent, or more of the plants in the islands 

 have fruit which is not buoyant, and could only be carried by 

 some accidental concurrence of circumstances. After talking 

 about the lists of sea-carried plants given by Schimper and 

 Hemsley, and including in each case about 120 species, he says: 

 "De Candolle was quite right in minimising the effect of currents 

 on the distribution of plants," and again, "one can scarcely 

 controvert Kerner's opinion that the dispersal of plants, as a 

 M'hole, is not appreciably affected by this process." Leguminosae 

 as a family are conspicuous among sea-borne plants. 



He considers that as an agency in stocking far outlying islands 

 birds take the first place, though there are many difficulties in 

 explaining the distribution. ^Vhy, for example, should Fiji have 

 about 200 genera not found in Hawaii or Tahiti, and yet many 

 of them just as well suited for bird carriage as those that actu- 

 ally occur there? He considers, however, that the age of bird- 

 dispersal is now practically over in the Pacific, and that just 

 like the plants the birds have tended to become local species 

 confined to islands or groups of islands. This phenomenon of 

 ciidvnmin or local species is shown most markedly in tlic case 

 of both plants and birds in the far outlying islands of the Pacific, 

 while in islands where none of the plants are peculiar, endemic 

 birds are few or wanting. 



He goes on to point out that the development of local species 

 is largely correlated with degree of isolation, not only as regards 



W.A. 2 



