CURRENTS OF THE ATLANTIC 



77 



an equal value in the reciprocal exchange of seed-drift between the 

 tropical regions on the opposite sides of the Atlantic. When we come 

 to balance the account respecting the interchange of seed-drift 

 between the Old and the New World, we learn that in the " give- 

 and-take " process the gift from the New to the Old World would be 

 slight. All the seeds borne to Europe in the Gulf Stream from the 

 West Indian region would find uncongenial climatic conditions that 

 would deprive the gift of any value. But better prospects would 

 await those that chanced to be diverted south, either in the vicinity 

 of the Azores, or further east in approaching European waters, 

 where they would come within the influence of the Portuguese or 

 North African Current. In both events they might possibly be 

 stranded on the coasts of tropical Africa to the north of the Cape 

 Verde Islands; but, as indicated by the bottle-drift, the chances 

 are that they would not be stranded at all, but would be carried 

 back to the West Indies in the stream of the North Equatorial 

 Current. 



It is also highly probable that seed-drift from the Atlantic shores 

 of North America, from Cape Hatteras northward, might be at times 

 transported to the shores of Europe in the Gulf Stream drift, as is 

 indicated in the tabulated results for bottle-drift before given. 

 Such dispersal would be effective for the seeds of a few coast plants 

 of temperate latitudes; but the seed-drift derived by currents from 

 such regions is always small in amount and frequently ineffective 

 for purposes of reproducing the plant. In my book on Plant Dispersal 

 (pp. 429, 434, 438) it is shown that dispersal by currents is mainly 

 restricted to warm latitudes. Whilst in the tropics seed-drift is 

 abundant on the beaches, in the cooler regions of the globe it is 

 usually very scanty and often masked by other vegetable debris. 



Another possible way by which the New World might occasionally 

 present seed-drift to the Old World is afforded by the already 

 mentioned westward extension of the Guinea Current at certain 

 seasons of the year so as to constitute a counter equatorial current 

 (see Note 19 of the Appendix). Acting as a " backwater " to the 

 North and Main Equatorial Currents, it would be most effective in 

 returning African seed-drift to Africa ; but at times, by extending 

 nearer than usual to the New World, it might pick up a little drift 

 from the north-east coasts of South America. Then again, as 

 before suggested, it is probable that some of the drift gathered by 

 the Brazil Current from the shores and estuaries of Brazil south of 

 Cape St. Roque, as well as from the Rio de la Plata, might ultimately 

 find its way by the South Atlantic Connecting Current into the South 

 African Current and then into the Main Equatorial Current in the 

 Gulf of Guinea. But whether it would be beached on the South 

 African side seems unlikely, though there is an example of bottle- 

 drift which might be instanced in this connection (p. 63). 



In the above discussion I have made the most of the possible and 

 probable chances of the communication of seed-drift from the New 

 to the Old World. The gifts at most would be unimportant and 

 casual, and when effective of a belated kind. Not for a moment 

 could a comparison be made with the large amount of effective 



