438 A NATURALIST IN THE PACIFIC chap. 



Aleurites moluccana. With the exception of the last-named all 

 the fruits and seeds here enumerated are effectively dispersed by 

 currents over great areas. The sound nuts of Aleurites have no 

 buoyancy ; and the nuts only acquire their floating power through 

 the decay of the kernel (see p. 419). 



The beach drift of the American region, a region which 

 comprises both the Pacific and Atlantic coasts of tropical America 

 as well as the African West Coast, has some features in common 

 with the Asiatic beach-drift and other features peculiar to itself. 

 The plants, however, that are represented in the drift of both regions 

 are comparatively few, and none of the large fruits of the Asiatic 

 region are here to be noticed. We observe, however, that the drift 

 of the two regions possess in common the seeds of Caesalpinia 

 Bonducella, Canavalia obtusifolia, Entada scandens, Erythrina, 

 Mucuna, Sophora tomentosa, and Vigna lutea, all belonging to the 

 Leguminosae ; and to these we must add the seeds of Hibiscus 

 tiliaceus and of Ipomea pes caprae, and the seedlings of Rhizo- 

 phora and Avicennia. (Avicennia occurs in tropical Asia, but not 

 in Polynesia.) The distinctive characters of the beach-drift of 

 both coasts of America and of the west coast of Africa would be 

 shown in the presence of seeds of Anona paludosa, the fruits of 

 Laguncularia racemosa, Conocarpus erecta, Spondias lutea, and 

 other plants. But the beach-drift of the American region is much 

 more scanty. Of the shore plants generally dispersed in this 

 region there could not be more than a couple of dozen that are 

 indebted for their wide dispersal to the currents, and these alone 

 figure in the effective beach drift. In the Asiatic region these 

 plants would number at least seventy or eighty. 



Summary. 



(1) Effective dispersal by currents is mainly restricted to warm 

 latitudes, as is indicated by the scanty character of the seed-drift 

 stranded on the beaches of the south of England, Scandinavia, the 

 Mediterranean, and Southern Chile. 



(2) The present distribution in temperate latitudes of littoral 

 plants possessing buoyant seeds or seed-vessels is to be attributed 

 more to the influence of geographical and climatic conditions than 

 to the agency of currents. With some of them, such as those that 

 occur on both sides of North America, it is evident that their 

 distribution antedates the present climatic conditions within the 

 Arctic Circle. 



