II THE FLORAS OF THE PACIFIC ISLANDS 19 



undescribed species that I found in the mountains of Vanua Levu 

 sink at once. Another Fijian inland species (B. edulis, Seem.) that 

 is often planted, has fruits that float heavily for about a month. 

 This difference in buoyant powers is also associated with character- 

 istic differences in the structure of the fruits. It would be interest- 

 ing to learn what floating capacity belongs to those of the Samoan 

 endemic species (B. samoensis, Gray). Professor Schimper's obser- 

 vations on the genus in the Malayan region point in the same 

 direction, but more than one difficulty awaits its solution in the 

 re-examination of the genus. He says, however, that B. excelsa, 

 Bl., a Malayan species, sometimes cultivated and growing both 

 inland and at the coast, has fruits that floated for one hundred 

 days after drying (p. 173). 



A striking instance of this principle is afforded in the case of 

 the two Fijian species of Tacca, the wide-ranging littoral species, 

 T. pinnatifida, where the seeds float for several months, and the 

 inland species, T. maculata. Seem., found also in Australia and 

 Samoa, where the seeds sink at once or in a few days. The seeds 

 of the shore plant owe their buoyancy to the spongy tissue in 

 their coverings, which is either absent or much less developed 

 in those of the inland species. This point might also be deter- 

 mined for the new Samoan inland species described by Reinecke, 

 the German botanist, as T. samoensis. 



Another good illustration is afforded by the two species of 

 Premna of the South Pacific, though here the buoyancy of the 

 " stone " of a drupe is concerned. With P. taitensis or P. integri- 

 folia, a small littoral tree or shrub, these stones possess great float- 

 ing-power, and are often found in the floating seed-drift of the 

 Fijian estuaries and in the stranded drift of the beaches. In the 

 case of Premna serratifolia, an inland tree of moderate size, the 

 stones have as a rule little or no buoyancy. As shown in Note 32, 

 where this genus is discussed in detail, the buoyancy is mainly due 

 to empty seed-cavities. 



Other instances might be given in illustration of this principle ; 

 but it will have been noticed that already many of the familiar 

 trees and shrubs of a tropical beach have been mentioned in 

 this connection either by Professor Schimper or by myself. There 

 are other genera that afford similar indications but in a less direct 

 fashion. 



For instance, there are three widely spread Leguminous beach 

 plants of the Pacific, Erythrina indica, Canavalia obtusifolia, and 

 Sophora tomentosa, none of which are found in Hawaii ; but 



C 2 



