178 A NATURALIST IN THE PACIFIC chap. 



since it grows in the interior of the Panama Isthmus, and rivers on 

 the north and south sides now carry its seeds seaward from the 

 same " divide" to the Atlantic and Pacific Oceans, as described in 

 Chapter XXXII. 



But, as I have also shown in Chapter VIII, America forms with 

 the West Coast of Africa a region characterised by the same 

 tropical littoral flora. This region, on account of the arrangement. 

 of the currents, stands in a very peculiar relation with the Asiatic 

 region, which comprises the rest of the tropics, and to a great extent 

 possesses its own peculiar strand-flora. There are a few littoral 

 plants, like Entada scandens, Canavalia obtusifolia, Sophora tomen- 

 tosa, and Ipomea pes caprse that occur in both areas ; but the 

 large majority are confined to one or other of them, either to 

 the American region, including the African West Coast, or to the 

 Old World region, which includes the African East Coast. The 

 American region gives to the Old World, but it can receive nothing 

 in return. For this reason, it is argued, we are compelled to regard 

 most, if not all, of the cosmopolitan tropical shore plants that are 

 dispersed by the currents, such as those above named, as having 

 their home in the American region. Entada scandens would, there- 

 fore, from this standpoint have its home in America. 



Then, again, there is the difficulty connected with the distribu- 

 tion of this plant on both sides of tropical Africa. Though Oliver 

 in his Flora of Tropical Africa mentions this species only in 

 connection with the West Coast, he says it is probably widely 

 spread in that continent, and he refers to a pod in the Kew 

 Museum indistinctly labelled " Lake Ngami." I have not come 

 upon any reference to its being a littoral plant on the East Coast, 

 but since numerous littoral plants of tropical Asia are found on 

 that coast its occurrence there or in the East African islands would 

 be expected. However, as the genus has a centre in America, and 

 as this species is regarded as of American birth, we are not called 

 upon to employ the argument used in assigning to a non-American 

 genus like Afzelia an African home. Since the African West 

 Coast belongs to the American region of tropical shore plants 

 dispersed by the currents, the presence of Entada scandens on that 

 coast of Africa can be readily explained, whilst if it has reached 

 the Mala3'an Archipelago from America by way of the Pacific, it 

 would, by extending like many other Malayan coast-plants along 

 the shores of the Indian Ocean, almost complete its circuit of the 

 globe. It is in this fashion, I believe, that the other littoral plants,, 

 like Cassalpinia bonducella, Canavalia obtusifolia, and Ipomea pes 



