230 A NATURALIST IN THE PACIFIC ch. xx 



exceed a fourth part of that of Hawaii, it has the same number of 

 species. The Tahitian islands therefore display a predominance of 

 ferns and lycopods. 



(e) The non-effective influence of the greater elevation of the 

 Hawaiian Islands on its preponderance of peculiar species is shown 

 by comparing all the ferns and lycopods of the Fijian and Tahitian 

 Islands with those of the corresponding lower levels of the Hawaiian 

 Islands, when we find much the same contrast exhibited in the 

 number of peculiar species. 



(/) Whilst a large proportion of the ferns and lycopods are 

 common to all three groups, Hawaii possesses a number of 

 mountain species, widely distributed in temperate regions and on 

 the higher levels of mountainous areas in the tropics, that are not 

 found either in Fiji or in Tahiti. Their absence from these two 

 groups is due to the insufficient elevation of the islands and to the 

 non-existence there of extensive areas of any altitude. 



(^) The agency of the winds in dispersing the spores of ferns 

 and lycopods has been relatively uniform through the ages when 

 compared with the varying agency of the migrant bird, to which 

 the flowering plants mainly owe their distribution. Thus it is that 

 in the Pacific islands the vascular cryptogams have experienced 

 much less differentiation than the flowering plants, though as a rule 

 far older denizens of the islands. Yet we cannot doubt that the 

 same principle has been at work in both cases, the difference 

 arising in the instance of the flowering plants from the interrupted 

 and often suspended agency of birds in the work of dispersal. 



(//) It is a question whether there is not something more 

 concerned in the isolation of the Hawaiian group than its mid- 

 oceanic position, since effects almost as great have been produced 

 in continental regions. 



