154 A NATURALIST IN THE PACIFIC Ch. xv 



characterises as a variety is not so generally distributed in the 

 group. We have to explain not only how the original species 

 reached the group, but also how they have been distributed over 

 the islands. The currents could scarcely have transported the 

 fruits as we now see them. Those of O. sandwicensis have only a 

 trace of a buoyant covering, and, judging from some fruits that I 

 examined, they could possess little or no floating power. Even the 

 most enthusiastic advocate of dispersal by birds must pause here ; 

 and there remains the view, supported by evidence of a striking 

 character, that the inland Hawaiian species are derived from littoral 

 species that, having been originally brought by the currents, like 

 O. parviflora in Fiji, abandoned the beach and took to the 

 mountains, where they have become differentiated. 



It is probable that the lesson of Ochrosia in Hawaii can be 

 applied to one or two of the other Hawaiian " difficulties," and 

 that plants that now set at defiance all the attempts of the student 

 of dispersal to explain their occurrence in this group may have 

 commenced their existence in these islands as littoral species 

 brought originally by the currents and afterwards driven off the 

 beach. One of the greatest enigmas of the Hawaiian flora is 

 connected with another small Apocynaceous tree peculiar to the 

 group and described by Hillebrand as Vallesia macrocarpa and by 

 other Hawaiian botanists as a species of Ochrosia. Schumann, 

 however, places it in a new genus, Pteralyxia, near to Alyxia, 

 a genus already in the islands. However this may be, its dry 

 drupaceous fruits two inches (5 cm.) in length, and its pyrenes 

 almost as long, could never have been transported as such by the 

 birds of our own time ; and if they could have been carried in the 

 stomach of a bird given to the dietetic humours of the cassowary, 

 such birds in their trans-oceanic passages would have left some 

 trace behind in the groups of the mid-Pacific. In our perplexity 

 we read again the lesson of Ochrosia. 



Summary of Chapter (see end of Chapter XVI.). 



