WEST INDIAN BEACH-DRIFT 



3 



and in a large island like Jamaica this is not a light undertaking. 

 Even with Grisebacfrs Flora of the British West Indian Islands at my 

 disposal, a work that bears especially on Jamaican plants, it was 

 not possible to say with certainty that three of the most interesting 

 plants represented in Jamaican beach-drift, Carapa guianensis, 

 Manicaria saccifera, and Sacoglottis amazonica, though not accredited 

 to the island, did not still survive in some of its extensive coastal 

 swamps. It will, however, be subsequently shown that in the light 

 of more recent investigations the probability of their not existing 

 there is very great. 



These are difficulties likely to crop up in the case of all large 

 tropical islands. Yet the incrusting cirripedes, Serpulce, and other 

 organisms will frequently aid us in determining whether any par- 

 ticular fruit or seed is from beyond the sea. It is only the outlying 

 sand-key, such as occurs in the Turks Islands, that affords the 

 opportunity of safely differentiating the foreign drift on a beach. 

 Here after a few weeks spent in examining the local flora there is 

 little or no trouble in making the discrimination. 



The riverside vegetation above the mangroves, the mangrove 

 formation of the estuary and of the coast swamp, the plants of the 

 beach and its border, all contribute to the floating drift of these seas. 



River-drift above the Mangroves. — A good deal of the materials 

 brought down by the river, and I have in this sketch the Black River 

 of Jamaica chiefly in my mind, consists of aquatic plants, such as 

 Pontederias and Pistias, and of foliage, portions of tree-branches, 

 etc., which do not count in distribution, and in the case of the floating 

 plants are soon destroyed by the salt water or dry up when stranded 

 on the beaches. These aquatic plants form a special feature of the 

 floating drift of rivers of tropical America, and I have referred to 

 them in the instance of the Guayas River in Ecuador in my book on 

 Plant Dispersal (p. 488). Yet the plants of the riverside and of the 

 wooded slopes of the river-valley above the mangrove-bordered 

 estuary add a great variety of fruits and seeds to the drift floating 

 in the stream, as illustrated in the description of the Black River 

 given near the close of this chapter. 



Many of these floating fruits and seeds have little or no effective 

 value for distribution except along the same river-system. Thus in 

 the Black River drift occur in numbers the germinating fruits of 

 Grias cauli 'flora, the germinating seeds of Symphonia globulifera, of 

 Crinnm. and of Crudya spicata ; and one may add the seeds of 

 Fevillea cordifolia, which even when they escape the fate of germina- 

 tion in the river-drift are far from suited for dispersal over the sea. 

 It is of importance to remember that through this tendency to germin- 

 ate when afloat many of the seeds and fruits of the drift of tropical 

 rivers are rendered useless for purposes of dispersal even across 

 narrow tracts of sea. 



But amongst the fruits and seeds found afloat in West Indian 

 river-drift, excluding those supplied by the mangroves and their 

 associates, many others have no effective value for purposes of dis- 

 tribution. Although the gourds of Crescentia trees and the fruits 

 of Acrocomia palms are characteristic of this floating drift, the first 



