xiv LITTORAL AND INLAND PLANTS' RELATIONSHIP 139 



species in Hawaii. Besides Vigna lutea, the beach species, which 

 is found not only all over the Pacific islands but on the tropical 

 beaches of the Old World, there are in Hawaii two endemic species 

 (V. sandwicensis and V. oahuensis) that occur in the mountains, 

 usually at elevations of from 1,500 to 5,000 feet ; but I do not find 

 any more inland species recorded from the other Polynesian 

 archipelagoes. It may at first be noted that Vigna lutea, which in 

 some parts of the world strays inland, displays considerable variety 

 in its littoral station in the Pacific. Thus, in Hawaii, I found it 

 sometimes on the sandy beach, sometimes on a rocky shore, and 

 sometimes on the edge of old lava-cliffs overlooking the sea. In 

 Fiji, though usually a trailer on the beach, it may become a climber 

 hanging from the trees bordering the creeks in the mangrove- 

 swamps. Though Hillebrand makes no mention of forms inter- 

 mediate between coast and inland species in Hawaii, I found in one 

 locality at the coast some specimens of Vigna lutea displaying the 

 twisted pods and two callosities on the standard that are charac- 

 teristic of V. sandwicensis, one of the inland species. The seeds 

 of Vigna lutea float in sea-water unharmed for months, and they 

 are to be found in the stranded drift of the Hawaiian and Fijian 

 beaches, and floating in the drift of the Fijian rivers. I was unable 

 to obtain the mature seeds of the inland species, and it has there- 

 fore yet to be determined whether they follow the rule in the loss 

 of buoyancy. It may be added that a plant of Vigna lutea 

 raised in Hawaii from seed displayed some small tubers of the size 

 of a pea on its roots. 



The case for Premna is stated in Note 32. In this genus, as 

 with Vigna, the final test of experiment is needed ; but the data at 

 my disposal point to the probability that an inland species has 

 here been derived from a littoral plant. 



The summary of this chapter is given at the end of Chapter 

 XVI. 



