354 A NATURALIST IN THE PACIFIC chap. 



or, as with Polygonum, possess a cosmopolitan species (P. glabrum) 

 ranging over the warm regions of the globe. Even Osteomeles 

 presents no exception to the rule, since the Pacific plant is the only 

 one of its species that is not American. 



We have in Polygonum glabrum the only aquatic or semi- 

 aquatic plant widely distributed over the Pacific islands that can 

 lay claim in all groups to be indigenous. It is associated in 

 Hawaii with species of Potamogeton and Naias, aquatic genera 

 that have, however, a limited distribution in Polynesia. 



I will now make a few remarks on each genus such as bear on 

 their distribution and on their mode of dispersal in the Pacific. 



Rhus (Anacardiacese). — The representation of this genus by 

 indigenous species in oceanic islands not only in the Pacific but 

 also in the Atlantic, as in the Bermudas, is of especial interest in 

 connection with dispersal by frugivorous birds, since the drupes are 

 typically dryish and might appear to be not very attractive to 

 birds. There are two Old World species known from the Pacific 

 islands : one being R. simarubaefolia (Gray), distributed over the 

 South Pacific groups from Fiji to Tahiti and hailing from Malaya ; 

 the other, R. semialata (Murray), alone recorded from the Hawaiian 

 Group and derived probably from China or Japan. This indication 

 that the groups of the North and South Pacific have derived their 

 species, the first from Temperate Asia and the second from Tropical 

 Asia, is of some interest. In Samoa, according to Reinecke, the 

 fruits of R. simarubaefolia, which are of the size of a pea, form the 

 favourite food of the fruit-pigeons. That birds disperse the seeds 

 of the various Sumachs is familiarly known. In the United States, 

 as we learn from Barrows, Beal, and Weed, crows, woodpeckers, 

 and other birds feed extensively in winter on the fruits of different 

 species of Rhus, including the Poison Ivy (R. toxicodendron). 

 The crows discharge the seeds in pellets after retaining them for 

 about thirty minutes. Some seeds we must infer would pass into 

 the intestines, where they might be retained for ten to twelve hours 

 (see Chapter XXXIII.), which would be long enough, according to 

 Gatke's views of bird-velocity, to enable them to be transported 

 over a thousand miles of ocean. 



Osteomeles (Rosaceae). — One of the most interesting cases of 

 dispersal in recent times over the Pacific islands is that of O. 

 anthyllidifolia. Of the ten known species of the genus, nine are 

 confined to South America ; whilst the Pacific species, which is 

 not recorded from America, has been found in Upper Burma, 

 Japan, the Liukiu and Bonin Groups, Hawaii, Pitcairn Island, 



