TKANSACTIONS Oi' THE SKCTIONS. 107 



families whicli abound iu other parts of Polynesia are totally wantiug. Now much 

 of the poverty and exceptional distribution of the plants of these islands is pro- 

 Ijably duo to the great scarcity of flower-frequenting insects. Lepidoptera and 

 Ilvnieuoptera are exceedingly scarce iu the eastern islands of the Pacific, and it is 

 almost certain that many plants which require these insects for their fertilization 

 have been thereby prevented from establishing themselves. In the western islands, 

 such as the Fijis, several species of butterflies occur in tolerable abundance, and no 

 doubt some flower-haunting Ilymenoptera accompany them ; and in these islands 

 the flora appears to be much more varied, and especially to be characterized by a 

 much greater variety of sliowj' flowers, as may be seen by examining the plates of 

 Dr. Seemann's ' Flora Vitiensis.' 



Darwin and Pickering both speak of the great preponderance of ferns at Tahiti ; 

 and Mr. Moseley, who spent several days in the interior of the island, informs me 

 that " at an elevation of from 2000 to 3000 feet the dense vegetation is composed 

 almost entirely of ferns. A. tree fern (Alsophila tahitensis) forms a sort of forest to 

 the exclusion of almost every other tree, and, with huge plants of two other ferns 

 (Anr/iopteris cvecta and Aspelenium nidus), forms the main mass of the vegetation." 

 And he adds, " I have nowhere seen ferns in so gi-eat proportionate abundance." 

 This unusual proportion of lerns is a general feature of insular as compared with 

 continental floras ; but it has, I believe, been generally attributed to favourable 

 conditions, especially to equable climate and perennial moisture. In this respect, 

 however, Tahiti can hardly differ greatly from many other islands, -which yet have 

 no such vast preponderance of ferns. This is a question that cannot be decided by 

 mere lists of species, since it is probable that iu Tahiti they are less numerous than 

 in some other islands where they form a far less conspicuous feature in the vege- 

 tation. The island most comparable -ndth Tahiti in that respect is Juan Fernandez. 

 Mr. Moseley writes to me : — " In a general view of any wide stretch of the densely 

 clothed mountainous surface of the island, the ferns, both tree ferns and the un- 

 stenimed forms, are seen at once to compose a very large proportion of the mass of 

 foliage." As to the insects of Juan Fernandez, Mr. Edwyn C. Reed, who made 

 two visits and spent several weeks there, has kindly furnished me -with some exact 

 information. Of butterflies there is only one {Piirameis carie), and that rare — a 

 Chilian species, and probably an accidental straggler. Four species of moths of 

 moderate size were observed (all Chilian), and a few larvae and pupje. Of bees 

 there were none, except one very minute species (allied to Chilicolu), and of other 

 Ilymenoptera a single specimen of Ophion htteus (a cosmopolitan ichneumon). 

 About twenty species of flies were observed, and these formed the most prominent 

 feature of the entomology of the island. 



Now, as far as we know, this extreme entomological poverty agrees closely with 

 that of Tahiti; and there are probably no other portions of the globe equally 

 favoured in soil and climate, and with an equally luxm-iant vegetation, where 

 insect-life is so scantily developed. It is curious, therefore, to find that these two 

 islands also agree in the wonderful predominance of ferns over the flowering plants 

 — in individuals even more than in species ; and there is uo difficulty in connecting 

 the two facts. The excessive minuteness and great abimdance of fem-spores causes 

 them to be far more easily distributed by winds than the seeds of flinvering plants, 

 and they are thus always ready to occupy any vacant places in suitable localities, 

 and to compete with the less vigorous flowering plants. But where insects are so 

 scarce, all' plants which require insect-fertilization, whether constantly to enable 

 them to produce seed at all, or occasionally to keep up their constitutional vigour 

 bv crossing, must be at a great disadvantage ; and thus the scanty flora which 

 oceanic islands must always possess, peopled as they usuall)' are by waifs and 

 strays from other lands, is rendered still more scanty by the weeding out of all 

 such as depend largely on insect-fertilization for their full development. It seems 

 probable, therefore, that the preponderance of ferns in islands (considered in mass 

 of individuals rather than in number of species) is largely due to the absence of 

 competing phsenogamous plants, and that this is in great part due to the scai-city 

 of in.sects. In other oceanic islands, such as New Zealand and the Galapagos, 

 where ferns, although tolerabh' abundant, form no such predominant feature in the 

 vegetation, but where the scarcity of flower-hauuting insects is almost equally 



