WEST INDIAN AND WEST AFRICAN FLORAS 91 



on both sides of the tropical Atlantic that could not possibly, as far 

 as its seeds or its fruits are concerned, have accomplished the ocean 

 traverse, we have in Sacoglottis amazonica another estuarine tree, 

 which, although it is restricted to the New World, presents in its 

 buoyant fruits some capacity for reaching the Old World. In the 

 first case other influences than those of currents have determined its 

 distribution. In the second case the determining factors have been 

 the arrangement of the currents and the insufficiently persistent 

 vitality of the seeds. Whilst the fruits of Sacoglottis amazonica 

 could perform the two years' traverse to the African coast by the 

 Gulf Stream route in the North Atlantic, the seeds would probably 

 lose their germinative power after six months. Though not im- 

 possible, the direct route by the Counter Equatorial Current is 

 largely negatived in this case by the extensive bottle-drift data given 

 in Chapter III. 



(c) Inland Plants growing occasionally at the Riverside. — In con- 

 nection with West Indian rivers there is another group of plants, 

 the fruits of which often fall into the stream from the parent plants 

 growing on the banks beyond the reach of the tide, and are then 

 carried down to the sea to be distributed far and wide by the currents. 

 The distinction, however, is a little artificial, since quite half of the 

 plants would be found at times on the coast ; and there are some, like 

 Entada scandens, which, though usually growing inland in the West 

 Indies, are typically littoral in their station in the Pacific islands. 

 This group can be subdivided into (a) those found in tropical West 

 Africa, such as the leguminous climbers, Entada scandens, Mucuna 

 urens, and Dioclea reflecca, and the trees, Andira inermis and Spondias 

 lutea ; and (b) those confined to the New World, such as Mammea 

 americana, Sapindus saponaria, Crescentia cujete, C. cucurbitina, and 

 the palms Astrocaryum and Acrocomia. 



Here there is a certain relation between distribution and fitness 

 for dispersal by currents. With the exception of those of Sapindus 

 saponaria, none of the fruits or seeds of the purely New World plants 

 could accomplish an ocean traverse of two or three months' duration 

 without loss of the germinative capacity, though capable of floating 

 for much longer periods in an ineffective state. But even Sapindus 

 saponaria may not prove to be an exception, since there are indica- 

 tions dealt with in the special treatment of the plant that it might 

 be regarded as an Old World species. Of the five plants also at 

 home in West Africa all but Andira inermis possess seeds or fruits 

 that could perform in safety the ocean passage from West Africa 

 to Brazil. In the case of the seeds of the leguminous climbers they 

 could do very much more, since these seeds retain their germinative 

 capacity after being carried in the Gulf Stream to the shores of 

 Europe. Andira inermis presents the same difficulty as Symphonia 

 globulifera. Though it occurs on both sides of the tropical Atlantic, 

 it is not able to cross it. 



(d) Beach Plants. — We come now to the beach plants, those that 

 border the beaches and thrive on the sandy tracts in the rear. They 

 arrange themselves into three groups : the cosmopolitan plants 

 extending in a general sense over the continental and insular coasts 



