278 A NATURALIST IN THE PACIFIC CHAP. 



of neighbouring large islands. Viola abyssinica, for instance, which 

 occurs in Madagascar, is spread over the elevated mountain ranges 

 of tropical Africa. With regard to the five Hawaiian species, it 

 may be remarked that three of them are bog species and two occur 

 in dry situations. The first are most characteristic of the moun- 

 tains, one species occurring on the summit of Mount Eeka, 6,000 

 feet above the sea. Judging from the stations alone, at least two 

 species were originally introduced into the Hawaiian Group. 



Viola seeds, as indicated by my experiments on the different 

 British species, including Viola palustris, are not buoyant, and 

 there is no possibility of the seeds being picked up by birds in 

 floating drift. There is, however, a possible means of dispersal in 

 birds' plumage by means of the mucosity of the seeds of some 

 species. Thus, although this is not exhibited, as shown by my 

 experiments, by Viola canina and V. palustris, it is well displayed 

 by the Field-Pansy (V. tricolor). I found that the seeds of this 

 species, after lying a little time in water, were thickly covered with 

 mucus, and that they adhered to a feather, on drying, as firmly as if 

 gummed. This did not, however, come under my notice in the 

 case of the seeds of one of the Hawaiian species, V. chamissoniana, 

 examined by me. One sometimes observes Viola canina in 

 England growing in places, as in the crevices and on the tops of 

 old walls, where its seeds could have only been carried by birds. 

 In some cases the propellent force of the seed ejected by the con- 

 tracting valves of the capsule would explain queer stations. In 

 its power of seed-expulsion, Viola chamissoniana, the common 

 Hawaiian species, is just as active as our British species. 



With regard to the Leguminous genus Vicia we have the 

 observation of Focke on the dispersal of its seeds by pigeons, as 

 described before on page 150. 



Sophora chrysophylla, the " Mamani " of the natives and one of 

 the most familiar of the trees of the Hawaiian mountains, is dis- 

 cussed at length in Chapter XV., where the difficulty of supposing 

 that its seeds could be transported unharmed in a bird's stomach 

 half-way across the Pacific is pointed out ; and it is suggested that 

 it was more probably derived from a littoral species brought by the 

 currents. However, the point is a debatable one, and the seeds of 

 the " Mamani " can scarcely be regarded as " impossible " from the 

 standpoint of dispersal. 



With reference to the possibilities of dispersal of the achenes of 

 Artemisia, some very suggestive indications are to be obtained 

 from a paper by Mr. D. Douglas on the North American Tetra- 



