WEST INDIAN AND WEST AFRICAN FLORAS 89 



fruits and seeds for transport across the Atlantic from the Gulf of 

 Guinea to South America in the Main Equatorial Current. We 

 are not concerned just at present with the indications that this test 

 might yield of a West African origin of many of the West Indian 

 littoral and estuarine plants. For the moment we will simply 

 regard this as a proof of capacity for accomplishing the traverse of 

 the tropical Atlantic. When we regard the twenty-one plants that 

 are restricted to the New World we find that only five, or 24 per 

 cent., respond to the test. It should here be repeated that the 

 list of plants confined to the New World could be considerably 

 augmented, and that the effect would be to markedly diminish the 

 proportion of those that respond to the test. With reference to the 

 five plants that are restricted to the New World, notwithstanding 

 their capacity for crossing the tropical Atlantic, we shall subse- 

 quently see that in negativing any reciprocal interchange of littoral, 

 estuarine and riverside plants between the Old and the New World 

 they afford a clue to the origin of most of the West Indian plants 

 of these stations that have been found in the Old World. 



(A) Its Application to the Plants in the Mass. — The issue 

 may thus be stated. Whilst nearly 90 per cent, of the plants that 

 are common to the West Indies and West Africa possess seeds or 

 fruits that could be transported by the currents from the Gulf of 

 Guinea to Brazil, less than one-fourth of those restricted to the 

 West Indian side possess the same capacity, but have not extended 

 their range outside the New World. The matter thus resolves itself 

 into a question of the opportunities offered by the Atlantic currents, 

 concerning which it has already been brought out in Chapter III. 

 that whilst the Main Equatorial Current offers a ready and rapid 

 means of transport for fruits and seeds from West Africa to the 

 New World, the opportunities of West Africa receiving West Indian 

 seeds and fruits in a sound condition are small. Reference may here 

 again be made to the fact that De Candolle in his work on Botanical 

 Geography (pp. 763-4) places an equal value on the Gulf Stream 

 and the Equatorial Currents of the Atlantic in the reciprocal exchange 

 of drift between the opposite tropical regions. This is a serious 

 error, since the long circuitous route by the Gulf Stream, which 

 would involve a minimum passage of two years, would for all but a 

 very few leguminous plants negative any chance of effective dis- 

 persal. The Brazilian Current would not tap the West Indian region 

 at all, and the return of any of its seed-drift to tropical Africa would 

 involve a very lengthy passage and a somewhat complex series of 

 current connections. The only chance would be that offered by 

 the Equatorial Counter Current ; but it is shown that the occasions 

 in which it would extend far enough to the west to tap the New 

 World as a source of drift would be few, though not altogether 

 negligible. 



(B) Its Application to the Plants according to their 

 Station. — Having applied this test to the plants in the mass we will 

 now apply it to them according to their station. 



(a) The Mangroves. — In the first place come the mangroves and 

 their associates, all of which are West African as well as West Indian. 



