4 PLANTS, SEEDS, AND CURRENTS 



named carry seeds that have a fleeting vitality and the second float 

 only for a few days. Acrocomia fruits, it is true, are represented in 

 the drift of the Turks Islands, but merely in the form of the empty 

 44 stones," which, after being freed by the decay of the outer coverings 

 of the stranded fruit, acquire buoyancy only through the loss of the 

 seed. Then again both Andira inermis, a tree of the riverside, and 

 Mammea americana, a tree of the forested slopes of the river- valley, 

 add their fruits as a rule to the floating drift ; but it is very doubtful 

 whether their seeds would be fit for germination when the fruits are 

 stranded on some distant island. 



The fruits and seeds carried down by a West Indian river from 

 the interior to the sea that would be fitted for crossing unharmed a 

 broad tract of ocean are comparatively few. Taking all the kinds of 

 seeds and fruits brought down to the sea by the Black River from its 

 basin above the mangroves, I don't suppose that twenty per cent, 

 would be capable of reproducing the plant after a traverse of a 

 hundred miles of ocean. The seeds which are brought down by a 

 Jamaican river from the interior to the coast in a sound condition 

 and capable of sustaining without injury the effects of prolonged 

 flotation in the sea, would include such leguminous seeds as those of 

 Entada scandens, Mucuna urens, and Dioclea reflexa, all of which 

 figure in the West Indian drift stranded in a sound condition on the 

 shores of Europe. Then there would be the 44 stones " of Spondias 

 lutea and the long pods of Cassia grandis, which, after they have been 

 transported by the rivers to the sea, would still be able to carry some 

 of their seeds unharmed far across the ocean. 



Drift supplied by the Mangrove Formation. — We come now 

 to the vegetation of the mangrove formation as a source of the floating 

 drift of West Indian seas. We have to distinguish here between 

 the true mangroves and their associates. Together they form colonies 

 everywhere, whether on the surface of some newly raised islet or 

 key, or on the coast, or in the estuaries of the larger islands. Rhizo- 

 phora mangle, Laguncularia racemosa, and Avicennia nitida are the 

 mangrove trees proper ; and one of their most prominent character- 

 istics is their viviparous habit, which, however, is less pronounced with 

 Laguncularia than with the others. The occasional associates of 

 the mangroves in the larger islands are Anona palustris and Carapa 

 guianensis. In Trinidad we find also Manicaria saccifera and Saco- 

 glottis amazonica together with a species of Bactris, a palm that grows 

 in similar situations. The Manicaria and Sacoglottis trees are con- 

 spicuous constituents of the estuarine floras of the great rivers of 

 Venezuela, the Guianas, and Brazil. Though they only just enter 

 the West Indian region, their fruits are distributed by the currents 

 far and wide over the Caribbean Sea. 



All the above-named trees of the mangrove swamps contribute 

 to the floating drift of these seas, the true mangroves being repre- 

 sented in the case of Rhizophora by long seedlings, in the case of 

 Avicennia by the germinating fruits and seedlings, and in that of 

 Laguncularia by the fruits, which are often in the germinating con- 

 dition. Uninjured by flotation in sea- water these seedlings and 

 germinating fruits are cast ashore, and very soon establish themselves. 



