190 PLANTS, SEEDS, AND CURRENTS 



tropical Africa, in the islands of the Indian Ocean, in the Malayan 

 Islands, and in Polynesia. With the exception of the African 

 coasts, which I have not visited, it came under my notice in all 

 the above regions. It ranks with Ipomoea pes-caprce as one of the 

 most ubiquitous of tropical strand plants. 



Yet, in spite of its world-wide distribution in tropical regions and 

 of the fact established by observation and experiment that the seeds 

 are dispersed by currents, the seeds present a strange fickleness 

 of behaviour under the test of experiment. The plant has been 

 discussed in detail in my book on Plant Dispersal; but I will here 

 allude to the results of buoyancy experiments given in that work 

 (p. 579). Of freshly gathered seeds placed in sea- water in Fiji 

 only 10 per cent, as a rule floated after three months. Of seeds 

 which had been kept for three years 50 per cent, floated after eleven 

 weeks. In an experiment on recently collected seeds in Jamaica 

 40 per cent, floated after a month. The explanation of this behaviour 

 is that on the average only 70 per cent, of the seeds are impervious 

 to water, a result obtained from more recent experiments and re- 

 corded in the author's Studies in Seeds and Fruits (p. 94). But the 

 proportion of impermeable seeds varies considerably, being sometimes 

 more and sometimes less ; and at any rate the impervious seeds can 

 float for long periods. The impermeable seeds retain their germinative 

 capacity for a long time. Prof. Ewart found that seeds, sixteen 

 years old, were able to germinate, though sulphuric acid was required 

 to start the process (Ibid., p. 96). 



The seeds were commonly observed by me in the drift of the 

 Eijian beaches and also on the coast of Ecuador, as well as on both 

 sides of the Isthmus of Panama, the plants being usually noticed 

 in the vicinity. I found them afloat in the drift of the Rewa estuary 

 in Fiji, and they were collected by Moseley amongst a number of 

 other floating fruits and seeds off the coast of New Guinea (Chall. 

 Bot., IV., 291). Though neither the seeds nor the plants were observed 

 by Treub on the shores of Krakatau three years after the great 

 eruption of 1883, the plant was found established by Penzig in 1897 

 and by Ernst and others afterwards. I came upon the seeds in 

 the beach-drift of different parts of the Jamaican coast, and they 

 were obtained by Morris from the beaches on the south side of the 

 island (Chall., Bot. IV., 291). They also came under my notice on 

 the beaches of St. Croix, Tobago, and other islands. 



The plant is universally distributed in the West Indies, and there 

 were few beaches visited by me that did not display it. It occurs 

 all round Jamaica, and I found it on nearly every beach examined 

 on the north, south, and west sides of the island. It was rarely 

 observed growing away from the coast. However, in Tobago I 

 noticed it a mile inland and about 250 feet above the sea. In the 

 Turks group it is very rare, and was only remarked on two of the 

 ten islands — namely, on Salt Cay on the east side, where a fair-sized 

 colony was thriving on the beach, and on Grand Turk, where it was 

 represented only by a solitary seedling growing in the beach-drift 

 and evidently derived from a seed thrown up by the waves. Accord- 

 ing to Millspaugh it was recorded by Lansing from seven of the nine- 



