vii THE HAWAIIAN STRAND-FLORA 57 



fore, the fruits of such Old World littoral trees as Barringtonia 

 speciosa, Cerbera Odollam, Guettarda speciosa, Ochrosia parviflora, 

 Terminalia Katappa, &c, that could be dispersed only by the 

 currents, have failed to reach Hawaii, it is essential to remember 

 that they have also failed to reach America. This suggests that 

 Hawaii may have received some of its littoral plants from America 

 through the agency of the currents ; and it is shown in the 

 following chapter that, as a rule, when a South Pacific plant 

 with buoyant fruits or seeds is not found in America, it is equally 

 absent from Hawaii. The question thus acquires quite a different 

 aspect, and we shall accordingly have to regard tropical America 

 in the next chapter as a possible centre of diffusion of littoral 

 plants over the globe, a centre possibly as important as that 

 connected with the tropics of the Old World. 



Although, however, the currents have played a part in stocking 

 the Hawaiian beaches with their plants, their share in the work has 

 been unimportant, and the number of plants concerned is limited. 

 If we take away the seven or eight littoral plants introduced by the 

 aborigines, as well as the three endemic species as indicated in the 

 list in Note 28, and then remove from the residue the plants with 

 small fruits or seeds possessing little or no buoyancy, there remain 

 only the following eight species, the presence of which in Hawaii 

 might be attributed to the currents, namely, Caesalpinia Bonducella, 

 Cassytha filiformis, Colubrina asiatica, Ipomea glaberrima, Ipomea 

 pes caprae, Scaevola Kcenigii, Vigna lutea, and Vitex trifolia. Of 

 these plants, three species, those of Cassytha, Scaevola, and Vitex, 

 possess fruits that would be likely to attract frugivorous birds, and 

 are in some cases known to be dispersed by them (see Chapter 

 XIII.); so that we are not in these instances restricted to the agency 

 of the currents. With the other five the currents offer the readiest 

 explanation, but, as is indicated in the cases of Caesalpinia Bondu- 

 cella and Ipomea glaberrima (Chapter XVII.), it is quite possible 

 that birds have occasionally intervened. Altogether we may infer 

 that in stocking the Hawaiian beaches with their littoral plants the 

 currents have taken a subordinate part. 



Coming to the Hawaiian littoral plants having seeds or fruits 

 that have no floating power, we find that they present a motley 

 group. It has been already remarked that this is the group of 

 shore plants that derives most recruits from the inland flora, and 

 that it is in this group that the differences between the shore-floras 

 of tropical regions find their expression. Yet a very odd collection 

 of plants is here exhibited. Sometimes the beach-flora is composed 



