VIII LITTORAL PLANTS AND CURRENTS OF THE PACIFIC 69 



of the mangroves. Each of the two regions has its own species, 

 none being common to both the American and Asiatic regions, 

 although, as is shown in Chapter XXX., the American species of 

 Rhizophora is now seemingly breaking its bounds and intruding 

 into the Pacific islands. On the other hand, some of the mangrove 

 genera, Avicennia, Carapa, and Rhizophora, are found all round 

 the globe, whilst others are restricted to one or other of the two 

 regions, Bruguiera, Lumnitzera, and Sonneratia, for instance, to 

 the Old World region, and Laguncularia to the American and 

 West African region. 



For convenience we may designate the two great regions of 

 tropical strand-plants, with buoyant seeds or fruits, the American and 

 the Asiatic regions, remembering that the first includes both coasts 

 of America as well as the African West Coast, whilst the second 

 extends from the East Coast| of Africa to Polynesia. Excluding 

 the ubiquitous species, these two regions are well distinguished from 

 each other. If we look at the chart of the currents we perceive the 

 reason of the American region including the West African Coast, 

 and we see why none of the indigenous plants of this region occur 

 on the African East Coast. So also with the Asiatic region, a 

 glance at the chart will show that all the portions of its area are in 

 connection with each other directly or indirectly through the 

 currents, and that only time is required for the transport of buoy- 

 ant seeds over most of the region. 



Hitherto I have mainly followed Professor Schimper in this 

 matter ; but since my visit to Ecuador and the Panama Isthmus 

 some further considerations have presented themselves to me. If 

 the reader will look again at the map of the curi-ents, he will 

 observe that there is little reason for supposing that the Asiatic 

 region can lend its littoral plants to the American region. On the 

 other hand there are greater facilities, as far as currents are con- 

 cerned, for America supplying the Asiatic region, namely by 

 means of the great equatorial currents that course westward across 

 the Pacific to the tropics of the Old World. 



It would therefore seem that the American region can receive 

 nothing by the currents from the Asiatic region. If accordingly it 

 gives but gets nothing back, we are compelled to assign an origin 

 in the American region to all littoral plants dispersed by the 

 currents that are found in the tropics around the globe. This is 

 what we have already regarded on other grounds as possible for 

 nearly all the littoral plants of the tropical Pacific with buoyant 

 seeds or seedvessels that are found in America. These plants are 



