234 A NATURALIST IN THE PACIFIC chap. 



apportioned them as in Seemann's results. The Tahitian region 

 here includes Eastern Polynesia. 



It is necessary before proceeding further to obtain a correct 

 idea of the significance of a large endemic element in the phanero- 

 gamic flora of a Pacific archipelago. We have therefore at the out- 

 set to inquire whether it is indicative of isolation or of antiquity. 

 If the number of peculiar genera is to be regarded as the test of the 

 relative antiquity of different Pacific floras and, by implication, of 

 the islands to which they belong, these three groups, as shown in 

 Table B, would arrange themselves in the following order, namely, 

 Hawaii, Fiji, Tahiti. This test might be reliable if the several 

 groups were in the same condition of isolation. Since, however, 

 as we have previously seen, the Fijian Islands still enjoy a fairly 

 free communication with the islands westward, whilst the Hawaiian 

 group is largely cut off, it is apparent that the tendency to generic 

 differentiation in Fiji might have been often swamped by immigra- 

 tion, and that Fiji with its much smaller number of endemic genera 

 may even be older than Hawaii. This objection does not apply 

 quite as forcibly to a comparison between Hawaii and Tahiti, yet 

 for reasons before given it may be regarded as sufficient to negative 

 any inferences concerned with relative antiquity. 



On account, therefore, of the great differences in the degree of 

 isolation of these three groups, we cannot be guided in our esti- 

 mation of the relative antiquity of their floras by their number 

 of peculiar genera. With the evidence at our disposal we are 

 compelled to accept the view, which indeed a single glance at a 

 map would suggest, that the number or proportion of endemic 

 genera is to be connected with the degree of isolation. Whether a 

 parallelism can be traced in the original stocking of these groups 

 with their earliest flowering-plants is a matter that can only be 

 elucidated by a further analysis of the peculiar genera. 



Synopsis of the Eras of the Flowering Plants in the 



Tropical Pacific. 



A. The Era of the Endemic Genera. — Mostly American in 

 their affinities. Represented particularly by Composite and 

 Lobeliaceae. 



B. The Era of Noil-Endemic Genera. 



(i) The mountain genera, either cosmopolitan in temperate 

 latitudes or derived from the New Zealand or the 

 Antarctic flora. Mostly represented in Hawaii. 



