INSULAR PLANTS AND INSECTS. 



269 



ocean ; as well as for the preponderance of certain orders 

 and genera. 



In Mr. Pickering's valuable work on the "Geographical 

 Distribution of Animals and Plants " (founded on his 

 researches during the United States exploring expedition), 

 he gives a list of no less than sixty-six natural orders 

 of plants unexpectedly absent from Tahiti, or which 

 occur in many of the surrounding lands ; some being 

 abundant in other islands — as the Labiatae at the 

 Sandwich Islands. In these latter islands the flora is 

 much richer, yet a large number of families which 

 abound in other parts of Polynesia are totally wanting. 

 Now much of the poverty and exceptional distribution 

 of the plants of these islands is probably due to the 

 great scarcity of flower-frequenting insects. Lepidoptera 

 and Hymenoptera are exceedingly scarce in 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 them- 

 selves. In the western islands, such as the Fijis, several 

 species of butterflies occur in tolerable abundance, and 

 no doubt some flower-haunting Hymenoptera 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 showy flowers, as may be seen 

 by examining the plates of Dr. Seeman's " Flora 

 Vitiensis." 



Darwin and Pickering both speak of the great pre- 

 ponderance 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 2,000 to 3,000 feet 

 the dense vegetation is composed almost entirely of 



