270 TEOPICAL NATURE, AND OTHER ESSAYS. 



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 {Angiopteris evecta 

 and Aspelenium nidus), forms the main mass of the 

 vegetation.'' And he adds, " I have nowhere seen ferns 

 in so great proportionate abundance.'* This unusual 

 proportion of ferns 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 in Tahiti they are less numerous than in some other 

 islands where they form a far less conspicuous feature in 

 the vegetation. The island most comparable with Tahiti 

 in this 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 unstemmed 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. Eeed, who made two visits and spent 

 several weeks there, has kindly furnished me with some 

 exact information. Of butterflies there is only one 

 {Pyrameis 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 pupae. Of bees there were none, except one 

 very minute species (allied to Chilicola), and of other 

 Hymenoptera a single specimen of Ophion luteus a 



