INSULAR PLANTS AND INSECTS. 271 



cosmopolitan idinenmon. About twenty species of 

 flies were observed, and tbese 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 

 luxuriant 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 no difficulty in con- 

 necting the two facts. The excessive minuteness and 

 great abundance of fern-spores causes them to be far 

 more easily distributed by winds than the seeds of 

 flowering 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 by crossing, must be at a great 

 disadvantage ; and thus the scanty flora which oceanic 

 islands must always possess, peopled as they usually are 

 by waifs and strays from other lauds, 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 scarcity of insects. In other 



