vii THE HAWAIIAN STRAND-FLORA 55 



Neither can the explanation be found in the deficient floating 

 powers of the seeds or seedvessels of many of the "absentees." 

 Those of Barringtonia speciosa, Guettarda speciosa, Heritiera 

 littoralis, the two species of Terminalia, &c., possess great buoyant 

 powers equal to, and probably often exceeding, those of the plants 

 that, like Ipomea pes caprae, have succeeded in establishing them- 

 selves in Hawaii. One has only to look at the lists giving the 

 results of flotation experiments in Notes 2 and 3, in order to 

 realise that there are very few of the " absentee " littoral plants, 

 the non-existence of which in Hawaii could be attributed to 

 deficient floating powers of the fruit or seed. Being able to float 

 unharmed for months, and in several cases even for years, the 

 seeds or fruits of the shore-plants unrepresented on the Hawaiian 

 beaches have been carried far and wide by the currents over the 

 tropical Pacific even to Ducie and Easter Islands, that is, as far as 

 the islands extend. 



The only plants about which one could express a doubt 

 concerning their ability to reach Hawaii through the agency of 

 the currents, and to establish themselves there, are the true 

 mangroves of the genera Rhizophora and Bruguiera. Since 

 germination takes place on the tree, it is only through the 

 floating seedlings that they could reach these islands ; but, as 

 shown in Chapter XXX., it is doubtful whether the seedlings would 

 be in a fit condition for reproducing the plant after such a long 

 oceanic voyage. If they had been as successful in establishing 

 themselves in Hawaii as they have been in the Liukiu Islands, 

 which lie in latitude a few degrees farther north, these two species 

 through their reclaiming agency would alone have prepared the 

 way for the whole mangrove formation. We have seen in the 

 preceding chapter that the absence of the mangrove formation 

 from Tahiti appears to be mainly due to the failure of the 

 pioneer species of Rhizophora and Bruguiera to establish them- 

 selves there. This evidently also applies to Hawaii, the cause of 

 their exclusion being connected neither with climate nor with 

 station, but as in Tahiti with the general unfitness of the floating 

 mangrove seedlings for crossing broad tracts of ocean without 

 injury to the growing plantlet. 



With regard, however, to the bulk of the " absentee " littoral 

 plants, those of the beach-formation, no such incapacity on the 

 part of the buoyant seed or fruit can be accepted. These plants, 

 which have reached Tahiti in numbers, have in the mass failed to 

 reach Hawaii. It will, therefore, be of interest to glance at the 



