80 A NATURALIST IN THE PACIFIC chap. 



as if they might safely be transported by the currents round and 

 round the globe ; and De Candolle very rightly placed this species 

 in his scanty list of plants dispersed by currents. Yet few seeds 

 are more treacherous when their buoyancy in sea-water is tested in 

 a warm place, as in a hot-house. They may take up water, swell, 

 and sink in a week, or they may float unharmed for a year. 



The seeds most exposed to this risk are those of the 

 Leguminous giant climbers, the lianes of the coast and inland 

 forests of the islands of the tropical Pacific. They belong to the 

 genera Mucuna, Strongylodon, &c. ; and thus several of the plants 

 that constitute for the student of plant-dispersal the enigmas of 

 the Pacific are here included. The seeds of Mucuna are especially 

 liable when afloat in sea-water under warm conditions to display 

 the early signs of germination, swelling up and sinking to the 

 bottom of the vessel, a process, however, soon arrested and 

 followed by the death of the embryo unless the seed is removed in 

 time. Yet the seeds of this genus are notably long " floaters." 

 Those of an American species, variously designated as Mucuna 

 pruriens D.C. and M. urens D.C., have long been known to be 

 washed ashore together with the seeds of Entada scandens on the 

 western shores of Europe, and particularly on the Scandinavian 

 coast, where they form regular constituents of what the Scan- 

 dinavian botanists correctly term the Gulf-stream Drift. 



Mucuna urens D.C. occurs with other American shore-plants 

 that are dispersed by the currents on the African West Coast ; and 

 there is no reason to doubt that its seeds perform the trans- 

 Atlantic voyage. It is found in Polynesia, in Hawaii, in the 

 Marquesas, and according to Reinecke also in Samoa ; and 

 probably it occurs in other groups. The specific determinations of 

 the genus, however, need thorough overhauling, so that it is not 

 possible to deal more than in general terms with the distribution 

 of a species. The distribution of Mucuna urens in the Pacific is, 

 however, irregular, and no doubt this is to be connected with the 

 uncertain behaviour of its seeds when transported by tropical 

 currents. The seeds would, I venture to think, often sink through 

 abortive germination in the warm areas of equatorial seas. 



When in Hawaii I kept ten of the seeds of this species 

 (M. urens D.C.) in sea-water for four and a half months, none of 

 them sinking in that period, the temperature of the water rarely 

 reaching over 8o°F., the average daily temperature being j6 — yf\ 

 However, when four years afterwards in England I placed five of 

 the seeds obtained at the same time in sea-water under conditions 



