20 



a very important role to fruit-eating pigeons, which are so abundant in 

 the Indo-Malayan region. He supposes that at some former period there 

 was a very active dispersal of plants through bird agency, which ceased 

 later for some unexplained reason. 



There are very serious objections to these views, when the Hawaiian 

 flora is considered. In the first place, we must assume an incredibly rapid 

 flight and endurance, which would bridge the immense distance, for ex- 

 ample, between Hawaii and South America or New Zealand, from which 

 such genera as Gunnera must have come, according to Guppy's hypoth- 

 esis. This genus, at present, comprises, as we have seen, about a dozen 

 species, mostly found in South America and New Zealand, with a single 

 species in the Malayan Archipelago and a couple in Africa. The species 

 inhabit wet, cool regions in Hawaii at elevations of about 4,000 feet. 

 To suppose that this plant has reached Hawaii by means of some fruit- 

 eating bird coming from South America or New Zealand is certainly a 

 strain on the imagination. 



The next difficulty lies in the nature of the existing bird fauna of 

 Hawaii. Aside from a number of American migratory shore birds and 

 water fowl, practically all of the birds are endemic, and a great majority 

 belong to a single peculiar family, Drepanididae, so modified that there 

 is doubt as to its relationships. It is thought that the present bird fauna 

 is descended from a very small number of original immigrants which 

 reached the islands at long intervals and at some very remote period. 

 None of the existing birds could have been responsible for the introduc- 

 tion of most of the plants, and if these owe their introduction to bird 

 agency, it seems strange that none of the birds responsible for this should 

 have left descendants in the islands. According to Guppy's hypothesis, 

 these bird visitors were fairly numerous and not merely occasional strag- 

 glers, and if this were the case it is hard to explain the complete absence 

 of such birds from the present fauna. 



It might also be asked what explanation can be offered for this active 

 migration. At present the migration of birds is due mainly to climate, 

 and it is hard to imagine such changes of climate as would induce a mi- 

 gration from the southern tropics to the northern ones. 



Guppy's theory as to the frequent bird visitors to Hawaii is also hard 

 to reconcile with his reference to the existing birds which are supposed 

 to be the descendants of a small number of immigrants which must have 

 reached the islands "far back in the Tertiary." 19 But he elsewhere" 

 states that the era of dispersal of the Malayan elements of the Hawaiian 

 flora, which he thinks reached the islands through bird agency, was prob- 



19 Loc. cit., p. 505. 

 " Lc . cit., p. 520. 



