256 A NATURALIST IN THE PACIFIC CHAP. 



three islands, usually adjacent, like Maui and Molokai ; and except 

 in the instance of two species of Lobelia and one species of Cler- 

 montia they never range over the length of the group. 



These facts speak eloquently of the suspension to a great extent 

 of the agencies of dispersal in recent times within the group. Some 

 corrections of the figures will be rendered necessary by future 

 investigations, but the main conclusion will not be materially 

 affected. Such facts are paralleled in the distribution of the 

 Hawaiian insects, mollusca, &c. ; but these matters need only 

 be mentioned here. We might, indeed, have expected, apart from 

 other considerations, that the isolation of the Hawaiian Lobeliaceae 

 from their kindred in other parts of the world would not have been 

 reproduced within the group itself. This, however, is not the case ; 

 and we now see that not only have they been deprived for ages of 

 their means of distribution over the Pacific, but that even within 

 the archipelago their transportal from island to island has been 

 largely suspended. We have before arrived at similar conclusions 

 with regard to the early Compositae, when we saw that about half 

 the species were not found in more than one island. It is there- 

 fore evident that the same great principle regulating the operations 

 of the distributing agencies has influenced to a similar extent both 

 the Compositae and the Lobeliacese of the Hawaiian Group. 



THE LOBELIACE^E OF THE TAHITIAN OR EAST POLYNESIAN 



REGION. 



The order is represented in this region by two endemic genera, 

 Sclerotheca of Tahiti and Rarotonga, and Apetahia of Raiatea. 

 These islands are, however, not sufficiently large for the extensive 

 development of the arborescent Lobeliaceae, such as we find in 

 Hawaii. The species in both genera are either arborescent or 

 shrubby ; but I do not gather that they give any character to the 

 floras of these islands. According to the data given by Drake del 

 Castillo for one of the two peculiar species of Sclerotheca occur- 

 ring in Tahiti, these plants grow on the humid wooded slopes of 

 the mountains at elevations of 2,000 to 3,000 feet. Whilst in one 

 species the plants attain a height of 10 to 25 feet, in the other they 

 do not exceed 10 feet. Rarotonga possesses a peculiar species of 

 Sclerotheca, 4 to 6 feet high, which was discovered by Cheeseman 

 growing plentifully on the upper slopes of the highest mountain of 

 the island at altitudes of 1,500 to 2,200 feet. The same botanist 

 also came upon a second species of the genus on another mountain 



