54 Means of Dispersal 



1. Ocean-currents. 



The seeds and fruits of strand-plants, such as occur everywhere 

 in the drift-zone of the coasts, are transported, almost without 

 exception, by sea-currents. In the case of many of these their 

 capacity for floating a considerable length of time in sea-water or 

 in salt-solution without losing the power to germinate, has been 

 demonstrated experimentally by Guppy 1 ,' Schimper, and others. 

 Floating capacity is not possessed in an equal degree by all strand- 

 plants. Some of them swim equally well whether freshly fallen 

 from the tree or in a dry state, while others can be carried by water 

 only after being dried. It is well known that such large drift-fruits 

 as coconuts, the fruits of Cerbera Odollam, Nipa fruticans, Bar- 

 ringtonia, Calophyllum, and Terminalia Catappa possess the power 

 of floating for a considerable time. Similarly small fruits and seeds 

 float for long periods. In Guppy's experiments the seeds of Gkiet- 

 tarda speciosa, Scaevola Koenigii, Morinda citrifolia, Tournefortia 

 argentea and others among the strand-plants which occur on 

 Krakatau, germinated after floating on sea-water for 40 to 53 days. 

 In Schimper's experiments seeds of Dodonaea viscosa germinated 

 after floating in a 3^ % solution of salt for 60 days, and Hibiscus 

 seeds germinated after 121 days. Similar experiments have shown 

 that other widely distributed strand-plants possess a much feebler 

 floating capacity. According to Schimper the seeds of Euphorbia 

 Atoto float for 4 to 5 days only ; Pemphis acidula seeds, as Guppy 

 demonstrated, sink at once when freshly fallen, and if left to dry 

 for 14 days they float only for 2 to 5 days. The cones of Casuarina 

 equisetifolia are said to float only for 1 to 2 days. While the short 

 floating period of 2 to 5 days is clearly insufficient to admit of the 

 transport of the seeds of the latter plant to islands situated a con- 

 siderable distance from the mainland, it is long enough to account 

 for its occurrence in Krakatau. The distance of the Krakatau islands 

 from the coasts of Java and Sumatra and many islands in the Sunda 

 Strait region is comparatively trifling. The island of Sebesi, which 

 was only partially deprived of its vegetation by the eruption of 1883, 

 is only 19 km. [12 miles] from Krakatau and only about 15 km. 

 [9 miles] from Verlaten and Lang islands. The distance of Krakatau 

 from Seboekoe is only slightly greater. To the nearest points of the 

 coast of Sumatra, Telong Kelapa and Varkenshoek, the distance is 



1 Gappy, H. B., loc. cit. The Solomon Islands, London, 18S7, p. 305. [The 

 subject of seed-dispersal is exhaustively treated by H. B. Guppy in his more recent 

 book, Observations of a Naturalist in the Pacific between 1896 and 1899, Vol. n. 

 London, 1906.] 



