366 A. NATURALIST IN THE PACIFIC chap. 



sand produced by the disintegration of the lava. Its small seeds 

 sink in sea-water even after prolonged drying ; and it can perhaps 

 be supposed that the original seeds were brought from North 

 America in the crevices of a drifting log. According to Ridley, 

 Fernando Noronha possesses a peculiar species also growing near 

 the sea ; and it may be that the drifting log has here been the 

 agent also : but in neither case would this explanation account for 

 the endemic character of the species. 



Cusciita (Convolvulaceae). — It would seem that with the ex- 

 ception of Hawaii, where an endemic species, C. sandwichiana, 

 occurs, no other oceanic group in the globe possesses a peculiar 

 species of the Dodders. With the exception of an endemic 

 species in New Zealand, and an introduced species in Fiji which is 

 found usually near the gardens of the white residents on Viti Levu, 

 the genus takes but little part in the Pacific floras. The Hawaiian 

 species is a characteristic beach-plant growing on Ipomea pes 

 caprae, Scaevola Koenigii, Tribulus cistoides, and on other plants 

 that find a permanent or a temporary abode on the beaches. We 

 learn from Ridley and Moseley that Cuscuta americana in 

 Fernando Noronha finds its host also in Ipomea pes caprae. Since 

 the seeds of the Hawaiian plant and of the introduced Fijian 

 species possess no buoyancy, even after drying for years, we cannot 

 look to the agency of the current unless we call the drifting log to 

 our assistance, and in that case the endemic character of the 

 Hawaiian species would present the difficulty already alluded to in 

 the case of Jacquemontia. The seeds of the Hawaiian plant are 

 about one-twelfth of an inch (2 mm.) in diameter, and as far as size is 

 concerned they might have been transported in a bird's stomach ; 

 but, on account of the rapidity with which the seeds of the genus 

 absorb moisture and swell up, it is most unlikely that they would 

 escape injury. This is one of the several difficulties in plant- 

 dispersal which New Zealand and Hawaii share in common. 

 Further remarks on the germination of the Hawaiian species are 

 made in Note 69. 



Riimex (Polygonaceae). — Hawaii possesses two peculiar species 

 of Rumex, a genus not recorded from any other of the Polynesian 

 groups. One of these species, R. giganteus, is a very remarkable plant, 

 growing to a height of thirty or forty feet when supported by trees. 

 It is noteworthy that the small group of Tristan da Cunha in the 

 South Atlantic possesses a species, R. frutescens, confined to those 

 islands (j^c/. Chall. Exped.,n. 154). Both Hawaii and Tristan da 

 Cunha lie in mid-ocean, cut off from the nearest continent by some 



