18 DERIVATION OF THE FLORA OF HAWAII 



The conditions in the two cases are very different, although there is a 

 certain apparent similarity. 



Krakatau lies less than fifty miles distant from Sumatra and Java, 

 with their extraordinarily luxuriant vegetation, whence in less than 

 twenty-five years (as the writer can testify from a visit made in 1906) 

 an abundant and varied vegetation had covered the completely devas- 

 tated island. 



A comparison of Hawaii, over 2,000 miles away from the nearest 

 mainland, and very much further away from the nearest habitat of most 

 of its genera, with the conditions existing on Krakatau, is certainly justi- 

 fiable only to a very limited extent. 



Guppy assumes, as was shown to be the case on Krakatau, that the 

 first immigrants were cryptogams of various sorts, ferns, mosses, lich- 

 ens, and blue-green algae. The spores of these plants are supposed to 

 have been carried by the wind. No details are given as to the relation- 

 ships of these plants, as they now exist, except in the case of the ferns, 

 where the statement is made that about half the species are endemic. It 

 is assumed that the introduction of fern spores by wind is still going on, 

 but no evidence of this is offered. 



While there is no question that many species of ferns, e. g., the com- 

 mon brake (Pteris aquilina), have spread rapidly over the world, owing 

 presumably to the ready transport of their spores by wind, this is not the 

 case with many other ferns, such as Osmunda and the Hymenophyllaceae, 

 whose delicate green spores very quickly lose their vitality and are quite 

 unfitted for wind transportation over great distances. The same thing 

 is true for many liverworts, and in this connection may be cited the case 

 of Krakatau, where no liverworts had been recorded in 1906, although 

 both Java and Sumatra are extraordinarily rich in these plants. It is 

 therefore hardly likely that the presence of the filmy ferns, for example, 

 can be explained by assuming that they have reached Hawaii from the 

 distant South Pacific through the agency of air currents. 



The great degree of endemism shown by the Hymenophyllaceae indi- 

 cates that they belong to the ancient flora. Of the four species of Hy- 

 menophyllum three are endemic and the fourth is known elsewhere only 

 from New Guinea. 



Guppy believes that the peculiar Compositae of Hawaii were among 

 the earliest immigrants and predicates an "Age of Compositae" antedat- 

 ing the influx of the plants from the southern hemisphere, which now 

 predominate. The Compositae are much better developed in Hawaii 

 than in Southern Polynesia, and have almost certainly been derived from 

 America. Guppy believes that birds were the principal agents of trans- 

 port; but in view of the facility with which the akenes of many Com- 



