160 PLANTS, SEEDS, AND CURRENTS 



I am not acquainted with the parent plant; but Hemsley states 

 that it climbs on trees on river banks in Central and South America 

 and in the West Indies (Chall. Bot., IV., 302). Pax, in the Pflanzen- 

 reich monograph on the Hippomanece (IV., 147, 1912), to which the 

 genus is referred, states that the distribution of this species extends 

 from the Antilles and Central America to Peru and Brazil. It is 

 found in the Amazon region, and here one may note Spruce's observa- 

 tion of its frequency amongst the riverside vegetation of one of the 

 tributaries of the Maranon branch of the Amazon on the lower 

 eastern slopes of the Ecuadorian Andes (Kew Bulletin, 1909, p. 216). 



Omphalea triandra, another species, which is dealt with on p. 226, 

 contributes to local beach-drift in the West Indies. Although the 

 seeds float and illustrate the same type of buoyancy, they lack the 

 hard crustaceous shell of those of 0. diandra, and are in this respect 

 less fitted for prolonged transport by currents. 



Acrocomia 



The empty " stones " of this genus of palms are common in 

 Jamaican beach- drift, and also came under my notice on the beaches 

 of Trinidad, Tobago, and Grenada, being doubtless in the main 

 derived from trees growing in the interior of the respective islands. 

 They may be regarded as characteristic of West Indian beach-drift, 

 though they are very scantily represented in the foreign drift of the 

 Turks Islands. Yet it is not easy to explain at first sight their 

 occurrence on beaches, since the palms especially affect savannas 

 and open woodlands, and seem to have no special preference for the 

 vicinity of rivers, by which the fruits could be conveyed to the coast. 

 However, that they are thus carried down to the sea is very evident. 

 (I have not distinguished here between the fruits of the two most 

 common species of the genus, A. lasiospatha and A. sclerocarpa). 



The moist mature fruits sink in sea-water, but they acquire 

 buoyancy in the drying process. However, experiment shows that 

 the dry fruits will sink in a few days or in a week or so, the outer 

 brittle shell being deficient at the base, which is imperfectly pro- 

 tected against the penetration of water by the small perianth. The 

 history of these fruits in West Indian drift is similar to that of 

 Aleurites moluccana in the drift of the Pacific islands, as described in 

 my book on Plant Dispersal (p. 419). The fallen fruits, having 

 become light and buoyant in the drying process, are washed into the 

 rivers and thus transported to the coast, where they are often 

 stranded on the beaches. Whilst lying there exposed to the sun and 

 rain, they are in time deprived of their outer coverings. The hard 

 black " stones," about an inch across, which are thus exposed, soon 

 lose their seeds through decay, and it is in this condition that they 

 usually occur in the beach-drift. The seeded " stone " has no 

 buoyancy either in the moist or the dry fruit. It is only when it 

 is set free by the removal of its coverings on the beach, and when 

 it has lost its seed by decay, that it is able to float. Each empty 

 " stone " has three lateral perforations, two of which are closed at 

 the bottom, but one is more or less patent. However, the sea- water 



