90 PLANTS, SEEDS, AND CURRENTS 



The true mangroves comprise Rhizophora mangle, Avicennia nitida, 

 and Laguncularia racernosa ; whilst their associates at the borders 

 of the swamp include Anona palustris, Carapa guianensis, and 

 Drepanocarpus lunatics. With all of them, except the last, con- 

 cerning which the requisite data are lacking, it is possible that the 

 Main Equatorial Current could have transported them from the African 

 coast to the shores of Brazil and the Guianas, but it would be under 

 varied conditions. Whilst Rhizophora would arrive in the form of 

 floating seedlings, with Avicennia and Laguncularia the germinating 

 fruits would be concerned. When pointing out in my book on 

 Plant Dispersal the obvious risks to which the seedlings and germi- 

 nating fruits would be exposed during a long ocean passage, I felt 

 constrained to admit (p. 77) that their capacity for effective dispersal 

 across an ocean must be postulated. 



At that time the position adopted was that America had supplied 

 West Africa with its mangroves. This I regard now as untenable, 

 and a later consideration of the current question, as discussed in 

 Chapter III., has convinced me that an average period of only twelve 

 weeks would be required for the transport of seed-drift from the Gulf 

 of Guinea to Brazil, whilst under especially favourable circumstances 

 this period might be reduced to two months. Though the seedlings 

 and germinating fruits of the mangroves could scarcely withstand 

 the wear and tear of an ocean passage of six months, it seems probable 

 that they would survive a passage of half this duration. With 

 regard to the floating seeds of plants like Anona palustris and Carapa 

 guianensis, which are associated with the mangroves, it is likely 

 that they could only accomplish an ocean traverse of from two to 

 four months with sound kernels. For long passages of many months 

 they would be quite unfitted as far as the preservation of their 

 effective condition is concerned. 



(b) The Estuarine Plants. — Apart from the mangroves and their 

 associates there are estuarine plants, such as Crudya spicata, Fevillea 

 cordifolia, Grias cauliflora, Manicaria saccifera, Sacoglottis amazonica, 

 and Symphonia globulifera, all of which contribute their seeds or 

 fruits to the floating drift that is borne seaward and distributed 

 by the currents. Whilst all the mangroves and their associates are 

 also West African, five of the six plants just named are confined to 

 the tropics of the New World. With the exception of Sacoglottis 

 amazonica there is not one of them, however, that gives promise of 

 being able to withstand without injury an immersion of months in 

 the sea, and this oddly enough is not the Old World plant. The 

 buoyancy of the seeds or fruits may be so great that as with Saco- 

 glottis amazonica and Manicaria saccifera the fruits have been known 

 to be stranded on the shores of Europe ; but the indications plainly 

 show that they would not be in a germinable condition. Yet it is 

 strange that the plant which is least fitted for oceanic dispersal, 

 namely, Symphonia globulifera, is the only one of the six that has 

 been found outside the New World, that is, in West Africa. This 

 plant is one of the puzzles of distribution, and we shall see its riddle 

 repeated in one or two other cases mentioned below. 



Whilst in Symphonia globulifera we have an estuarine tree growing 



