68 A NATURALIST IN THE PACIFIC chap. 



bears such a definite relation to the currents as America, and with 

 an ordinary chart of these regions their arrangement is to be 

 understood at a glance. Yet strange to say, as far as the distribu- 

 tion of tropical littoral plants is concerned, America holds a position 

 that the present system of the currents on its coasts will not 

 altogether explain. Within the lifetime of the species of mangroves 

 and other plants of the coast swamps that are found on both 

 the Pacific and Atlantic coasts of tropical America the two 

 continents of this name have been united by the emergence of the 

 Isthmus of Panama. 



Few things are more significant in plant-distribution than the 

 arrangement of the tropical littoral plants with buoyant seeds or 

 fruits, a subject that is discussed with some detail by Professor 

 Schimper in his work on the I ndo- Malayan strand-flora (page 190). 

 These plants group themselves into four sections : — 



(a) Those of the Pacific and Atlantic coasts of tropical America 

 (including the West Indies) and of the West Coast of Africa. 

 They include mostly plants of the mangrove-swamps and their 

 vicinity, such as Anona paludosa, Avicennia tomentosa, A. nitida, 

 Conocarpus erecta, Laguncularia racemosa, Rhizophora mangle, 

 etc. 



(d) Those of the Old World excluding the African West Coast 

 and extending from the East Coast of Africa eastward to the 

 Pacific islands. This is much the largest group and comprises 

 many of the plants named in the list given in Note 35 under Old 

 World species. One may cite as examples of plants ranging 

 almost all over this area, Barringtonia speciosa, B. racemosa, 

 Bruguiera gymnorhiza (in its most comprehensive sense), Carapa 

 moluccensis, Derris uliginosa, Guettarda speciosa, Hernandia 

 peltata, Heritiera littoralis, Pemphis acidula, Rhizophora mucronata, 

 etc. Plants of the mangrove-swamp and of the beach are, therefore, 

 here included. 



(c) Those occurring all around the tropics and including many 

 of the plants mentioned under Note 35 as Pacific island shore- 

 plants found also in America. Most of them belong to the Legu- 

 minosae, and there may here be mentioned Canavalia obtusifolia, 

 Caesalpinia Bonducella, Entada scandens, Gyrocarpus Jacquini, 

 Ipomea pes caprae, Sophora tomentosa, and Vigna lutea, 



(a) Those confined to a portion of the two great regions, such 

 as Nipa fruticans in the Old World, and the Manchineel (Hippo- 

 manes mancinella) to tropical America. 



It is to be noted that the ubiquitous species do not include any 



