FOREIGN DRIFT OF THE TURKS ISLANDS 151 



seed had no buoyancy, the pod must have owed its floating power 

 to the light, loose-textured husk. There is little to show that the 

 dry fruit would remain watertight for any length of time when 

 immersed in sea- water. The only protection the seed itself possesses 

 against the influence of sea- water is a thin permeable skin; and I 

 think that the death of the seed of the floating fruit would soon be 

 brought about through this cause. The pods probably reached the 

 Turks Islands after a week or two's drift from the neighbouring 

 coasts of San Domingo. 



For the reasons just given it would seem futile to look to the currents 

 for the explanation of the existence of this tree on both sides of the 

 tropical Atlantic. We have seen that since the West African region 

 must have borrowed this species from the New World, we are debarred 

 from appealing to the agency of the Equatorial Current in transport- 

 ing seeds and fruits from the Gulf of Guinea to the American conti- 

 nent. There remain only the possibilities of its reaching West Africa 

 by the westward extension of the Guinea Current or with the Gulf 

 Stream drift after it has crossed the North Atlantic. As shown in 

 Chapter III., the first route receives but scant support from the 

 evidence of bottle-drift, and the time required (at least six months) 

 would negative its practicability for the effective dispersal of this 

 tree. The objections would be still greater if we appealed to the 

 second route, which would involve an ocean passage of about two 

 years. In addition it is most unlikely, if plants like Saco glottis 

 amazonica and Hippomane mancinella, which are so much better 

 fitted for the Atlantic traverse, have failed to get away from America, 

 that a plant with the limited fitness for dispersal by currents 

 possessed by Andira inermis should be able to do so. 



Thus the currents fail to account for the occurrence of this tree 

 on the coast of West Africa. But it is just possible that the light, 

 empty pod might occur at times amongst European beach- drift, as 

 it would probably continue to float long after it had ceased to be 

 watertight. The great difficulty lies with the ill-protected seed. 

 Under natural circumstances its germinative capacity would soon 

 be lost, since the thin coats offer no protection against excessive 

 shrinkage, and it would seem likely that ordinary air-drying would 

 soon deprive it of vitality. 



Birds also fail us, since only a fruit-pigeon could carry such a 

 large fruit, and that would only be possible between neighbouring 

 islands or between adjacent insular and continental coasts. The 

 difficulties here raised resemble in some points those presented in 

 the case of the fruits of Chrysobalanus icaco, a plant also found on 

 both sides of the tropical Atlantic (see p. 193). But there is this 

 important difference in station. With the species of Chrysobalanus 

 the tree is essentially littoral, and thus the currents when carrying 

 the fruits to a distant coast would be bearing them to a suitable 

 station. With Andira inermis, however, the stranded fruits would 

 lie in most uncongenial conditions, conditions very different from 

 those which the tree favours in inland districts, as in the humid 

 forests of Porto Rico (Harshberger, pp. 685, 688) or by the riverside 

 in Jamaica. 



