CG TIIE VOYAGE OF EM.S. CHALLENGER. 



Bermudas, and two on the western coast of Tropical Africa. Two St Helena endemic 

 plants (see Part II., p. 34) are recorded from Ascension, but there are no specimens in the 

 London Herbaria corroborating this, and it is almost certain that there was some 

 mistake. 



St Helena. — In common with that of Juan Fernandez and some other islands, the 

 endemic element of the flora of St Helena includes a considerable proportion of arboreous 

 Composite:, the origin of which seems to be more remote and uncertain than that of the 

 rest. We have entered at some length into the distribution of arboreous Composita; 

 generally, without, however, arriving at any even probable solution of the problem of how 

 they reached these islands. Unlike the remainder of the element, the arboreous Compositse 

 of St Helena and Juan Fernandez are, to say the least, not more closely allied to the 

 Compositse of the nearest continents than they are of some more distant regions. The St 

 Helena Compositse, for example, exhibit quite as close a relationship to certain South 

 American and Australian genera as they do to African ; and the Juan Fernandez 

 Composite exhibit no less distinct affinities. In Chili the characteristic and prevailing 

 tribe of Compositse is the Mutisiaceee, which form, according to Bentham, nearly a third 

 of the whole number ; yet this tribe is not represented in Juan Fernandez ; but what is 

 more singular, the only Mutisiaceous genus in the Pacific islands is the very rare, 

 monotypic, endemic, arboreous Hesperomannia in the distant Sandwich Islands. On 

 the other hand, the remarkable Cichoriaceous Juan Fernandez genus Dendroseris has 

 no near relative in Chili, where the tribe is sparsely represented. With regard to the 

 very distinct Tahitian genus Fitchia, Sir Joseph Hooker acquiesces in the propriety of 

 placing it in the Helianthoidese rather than the Cichoriacese, in spite of its ligulate 

 flowers. The occurrence of arboreous Compositse in so many remote oceanic islands, 

 coupled with the distribution of the genera to which they bear the greatest affinity, seems 

 to indicate that they are the remains of very ancient types. We have not discussed the 

 probabilities of differentiation on the spot, because, even assuming that to have happened, 

 the difficulties connected with the great isolation of the insular types and their nearest 

 continental affinities have still to be met. The question by what means the ancestors of 

 these Compositse were conveyed to the islands — and unless a former continental connection 

 be supposed, conveyance from a continent seems the inevitable conclusion — can only be 

 conjecturally answered. Most of the Compositse are provided with exceptionally favour- 

 able means of dispersion in their light pappose achenes, though perhaps not for convey- 

 ance over immense expanses of the ocean; but we have yet much to learn on this point. 

 Wind seems at first the most probable agent ; but an uninterrupted current of air necessary 

 for the purpose is hardly imaginable ; and then, it might be asked, why has the agency, 

 whatever it was, ceased acting ? and why have its operations been bruited to the convey- 

 ance of seeds to the islands 1 why not from the islands as well ? 



