346 A NATURALIST IN THE PACIFIC chap. 



Elaeocarpus, Pleiosmilax, and Scaevola, possessing similar fleshy 

 fruits likely to be dispersed by frugivorous birds. 



The Alyxias indeed seem well suited for dispersal by birds. 

 The black fleshy drupes would readily attract them ; and the 

 solitary seed protected by a very tough horny albumen might be 

 ejected unharmed in their droppings. 



It would be possible to enter into similar detail with several 

 other genera of this period ; but here I can only direct attention to 

 their principal indications, permitting myself a little more license 

 when discussing the means of dispersal. 



Alphitonia (Rhamnaceae). — Amongst other genera with 

 polymorphous species closely following the lines taken by 

 Metrosideros in the Pacific is Alphitonia, a small Malayan and 

 Polynesian genus of tall trees, containing at most three or four 

 species, one of which (A. excelsa) has almost the range of the 

 genus and is found in most of the Pacific archipelagoes. So 

 variable is this widely-ranging tree that Bentham suggested that 

 there was only one species in the genus [Bot. Chall. Exped., iii. 

 133), a suggestion especially interesting in connection with the 

 role taken by polymorphous species in the Pacific. As bearing on 

 the mode of dispersal of this species, it may be observed that my 

 Fijian experiments show that the fruits are not fit for transport by 

 currents. With the mature drupe the outer coverings become 

 pulverulent, and the fruit breaks down, freeing the pyrenes which 

 do not float ; nor have the seeds any buoyancy. Although the dry 

 drupes would seem unattractive to birds, it is to birds we must 

 look for the dispersal of the genus. 



PlSOiNlA (Nyctagines). — Like Dodonaea, Metrosideros, and 

 Alphitonia, the cosmopolitan genus Pisonia possesses a poly- 

 morphous species that displays its variation in every Pacific group 

 and occupies a considerable number of stations. The earlier 

 botanists in the Pacific differed much as to the species of this 

 region, and this led Mr. Hemsley to observe in his paper on 

 the Tongan flora that it is difficult to understand the various 

 Polynesian and Australian species except on the assumption that 

 there is one very variable species. Recognising this difficulty, 

 Drake del Castillo deals somewhat summarily with nearly all these 

 forms, uniting them under one comprehensive species, P. umbellifera 

 (Seem.), thus constituting " une espece tres-polymorphe " that 

 ranges (generally in maritime districts) over tropical Asia and the 



