146 A NATURALIST IN THE PACIFIC chap. 



for dispersal by the currents, since they float, when unopened, only 

 for four or five days. Here also, as with Erythrina, the seeds of the 

 inland species no longer possess the buoyant kernels to which the 

 floating capacity of the seeds of the coast species is due. Though 

 we have to exclude the currents, we can scarcely in its case appeal 

 to bird-agency when we wish to account for the transportal of the 

 original seeds to Hawaii, as that would imply that birds can carry 

 beans nearly an inch, or 2 to 2'5 centimetres, in length unharmed 

 in their stomachs over a tract of ocean some 1,500 or 2,000 miles 

 across. We should have to learn much that is unexpected of the 

 modes of dispersal of the Leguminosae before we could accept such 

 an hypothesis. 



Canavalia galeata indeed presents to the student of dispersal 

 one of the enigmas of the Hawaiian flora ; and it should be noted 

 that the mystery of its distribution is concerned not only with the 

 means of transportal of the seeds of the original species to the 

 group, but also with its present dispersal among the islands. It is, 

 however, suggestive that Dr. Hillebrand mentions two varieties, 

 one of them found on Kauai, with somewhat smaller seeds ; so that 

 some inter-island differentiation is evidently in progress. No 

 attempt is made here to connect this inland species directly with 

 the absent beach-plants. That is a matter for the systematist ; but 

 we are not tied down to existing shore-plants in finding an ancestor, 

 since the common parent of the littoral and inland species may 

 have been a shore-plant dispersed by the currents. 



Mezoneuron. 1 



Another closely parallel instance, offering, from the standpoint 

 of dispersal, the same difficulties presented by Canavalia galeata, 

 is to be found in Mezoneuron kauaiensis (Hillebr.), a tall inland 

 shrub also peculiar to the group and belonging alike to the I 

 Leguminosae. The difficulties are so nearly identical that the 

 same explanation will have to cover both ; but it is significant that 

 with Mezoneuron there is no littoral species to which we can I 

 appeal to extricate us from the difficulty. Yet the genus is related 

 to CiEsalpinia, and the species was first described by Mann as 

 C. kauaiensis, so that it may have once possessed a littoral species 

 that has ceased to exist as such. When we come to discuss . 

 Caesalpinia and Afzelia (Chapter XVII.) we shall obtain from those 

 genera many suggestions as to the probable past of Canavalia 



