CH. XX THE AGE OF FERNS ' 221 



through the agency of the currents. The next era is represented 

 by the genera now peculiar to each group, since it is impHed that 

 they have descended from the earHest phanerogams that established 

 themselves in the group. The following epoch, which ends only 

 with the arrival of rhan, is characterised by the genera found out- 

 side the group ; and here different degrees of antiquity are indicated 

 according as the genus is represented wholly or in part by peculiar 

 species, or contains only species found in other regions. The 

 following eight chapters will be devoted to the development of the 

 method here briefly indicated. 



The Age of Ferns. 



It was established by Dr. Treub in the case of Krakatoa that 

 ferns and algae formed the earliest vegetation of this island after it 

 had been completely stripped of all its plants in the great eruption 

 of 1883. It is, therefore, but natural that the vascular cryptogams 

 should first be dealt with in any discussion relating to the historical 

 aspects of these floras. 



It has been before remarked that the epoch of ferns and lycopods, 

 which began with the earliest stage in the island's floral history, 

 may be regarded as extending to our own day. It is thus implied 

 that the vascular cryptogams of those early times are yet brought 

 there, and that, alike with the littoral plants, these ferns and lycopods 

 have witnessed almost unchanged the great revolutions that have 

 marked the history of the inland flowering plants, more particularly 

 those of the forest flora. This, as I will show, is true in Hawaii, 

 though only in a partial sense in comparison with the other island- 

 groups of Fiji and Tahiti, since in Hawaii nearly half the ferns and 

 lycopods are peculiar to that group, whilst in Fiji and Tahiti not 

 more than 8 or 9 per cent, appear to be endemic. (Rarotonga,. 

 according to Cheeseman, possesses one new species amongst its 

 seventy-two ferns and lycopods, and probably in this it is typical of 

 the smaller elevated islands of Eastern Polynesia.) 



The large proportion of peculiar Hawaiian species is the central 

 fact in the distribution of vascular cryptogams in the Hawaiian, 

 Fijian, and Tahitian archipelagoes, and indeed in the Pacific islands ; 

 and it is around this fact that much of the following discussion will 

 lie. (For the data relating to the Tahitian region, I have almost 

 exclusively followed Drake del Castillo.) 



On looking at the table given below, it will be noticed that 

 whilst there are about the same number of species of ferns and 



