236 PLANTS, SEEDS, AND CURRENTS 



for supposing on the grounds of the distribution of the genus that 

 America is the birthplace of this species. All the indications favour 

 the view that it has received it from the shores of the nearest portion 

 of Africa. 



In the case of Sccevola Plumieri another difficulty presents itself 

 in connecting its ranges on the East and West Coasts of Africa. 

 Though it reaches the Cape or its vicinity on the east side of the 

 continent, there seems to be a gap of about twenty degrees of lati- 

 tude on the west side between the Cape and Benguela, where, accord- 

 ing to the data supplied by Krause, it is next found. Probably 

 future records will bridge over this broad gap; and we can only 

 suppose that the species originally found its way north along the 

 African West Coast through the combined agencies of birds and of 

 inshore northerly currents. That it reached this coast from the 

 eastern side of the continent is very probable. This involves the 

 doubling of the southern extremity of Africa ; but it has been shown 

 in Chapter III. that this has been performed by bottle-drift. 



Tabulated Results of the Comparison of Scjevola Plvmiem, Vahl, 

 and scmvola k(enigii, vahl. 





Scaevola Plumieri 



Scaevola Koenigii 



Distribution. 



Pacific coast of tropical 

 America and the Galapagos 

 Islands. 



East coasts of tropical 

 America from Florida to Rio 

 de Janeiro, including the West 

 Indies and Bermuda. 



West Coast of tropical Africa 

 from Senegal to Benguela. 



East Coast of tropical Africa 

 from Somaliland southward 

 and extending to the Cape. It 

 reaches eastward to Southern 

 India, Ceylon, and Mauritius. 



Islands of the Indian Ocean 

 extending westward to the 

 Malabar coast, the Seychelles 

 and Madagascar, but not re- 

 corded from the east coast of 

 Africa. 



South-eastern Asia, extend- 

 ing north to the Liu-Kiu 

 Islands and eastward through 

 Malaya to New Guinea and the 

 northern coasts of Australia. 



Islands of the tropical Pacific 

 as far east as the Low Archi- 

 pelago and as far north as the 

 Hawaiian Islands. 



Characters of 

 fruit. 



Black juicy drupe. Stone 

 ovoid, markedly tubercled, 9 

 to 10 mm. long, no covering 

 of buoyant tissue, two -celled, 

 one cell empty. 



White fleshy drupe. Stone 

 roundish, slightly tubercled, 

 5 mm. across, possessing an 

 outer covering of cork-like 

 buoyant tissue, two -celled, 

 both cells holding a seed. 



Buoyancy of 

 fruits in sea-water. 



Stones float for four or five 

 months with seeds sound. 



Stones float for twelve 

 months and more with seeds 

 sound. 



Cause of the 

 floating capacity. 



Buoyancy of stone is en- 

 tirely due to the empty cell. 



Floating power of stone is 

 entirely due to the buoyant 

 tissue investing it. 



Agents of dis- 

 persal. 



Currents across tracts of 

 ocean. 



Frugivorous birds for local 

 dispersal. 



Currents across oceans. 

 Frugivorous birds for local 

 dispersal. 



