CH. xv LITTORAL AND INLAND PLANTS' RELATIONSHIP 141 



kernel ; whilst on account of the non-buoyancy of the kernel the 

 seeds of all the inland species possess no floating power. Some 

 very interesting points are raised in each of the three genera, and I 

 will first deal with the genus Erythrina. 



ERYTHRINA. 



If we look over the Pacific islands in search of a critical locality 

 for the investigation of the genetic relation between the littoral 

 and coast species of Erythrina, we discover it, as far as I can gather, 

 only in one group. In Fiji, Tonga, and Samoa we find only the 

 littoral species ; in Hawaii there is only an inland species ; whilst 

 in Tahiti occur both the littoral and the inland species E. indica,. 

 the wide-ranging shore-tree of the South Pacific, and E. mono- 

 sperma, the inland tree of Hawaii the last found nowhere else in 

 Polynesia, and confined to the Pacific. In Tahiti there are no 

 other species, and it is between these two species that the connec- 

 tion, if it exists, is to be sought. (Further details relating to the 

 genus are given in Note 53. In this place only the facts bearing 

 on the argument will be discussed.) 



The buoyant seeds of Erythrina indica are well known to be 

 dispersed by the currents ; whilst those of E. monosperma, as 

 obtained from Hawaii, have no floating power and sink at once, or 

 in a day or so, even after drying for two years. In Tahiti the first- 

 named species is a characteristic plant of the beach, whilst the last 

 grows there in the valleys and on the mountains up to elevations 

 of 700 to 800 metres. We have now to inquire whether there is 

 any decided affinity between the two species, and whether the 

 divergent characters of the inland species can be connected with 

 its station. With regard to the first query we may quote in reply 

 the observation of Drake del Castillo, that as concerning the foliage 

 and the inflorescence E. monosperma is very nearly related to- 

 E. indica, differing only from it in the more hairy calyx, in the 

 more permanently tomentose and much shorter pod, and in the 

 paucity of seeds (one or two in number). 



We will now see whether it is possible to connect these 

 differences in character with differences of station. Neither 

 Nadeaud nor Drake del Castillo give precise descriptions of 

 the station of Erythrina monosperma in Tahiti ; but Nadeaud and 

 Lepine remark that it grows on precipices as well as in the valleys 

 on the north or dry side of the island ; and we may infer that it 



