192 A NATURALIST IN THE PACIFIC chap. 



seeds thus treated swell in two days to three times their original 

 size and increase their weight fourfold. Water finds its way to 

 the nucleus or embryo partly through the dilated inner opening of 

 the micropylar passage and partly through the inner skin. The 

 nucleus then swells up into a fleshy mass, filling the seed-cavity, 

 and in two or three days more germination begins. 



I pass now to the discussion of the buoyancy of the seeds. 

 Considering that both species occur in oceanic islands, and that the 

 currents are active agents in transporting the seeds, their behaviour 

 under experiment appears at first sight to be full of anomalies. 

 Thus, it was ascertained at Kew {Bot. Chall. Exped. iv., 301), both 

 with comparatively fresh and with older seeds, that those of 

 Caesalpinia bonducella floated in salt water, whilst those of 

 C. bonduc sank ; but in the record given of the experiment no 

 mention is made of the original station of the parent plants ; and it 

 will be shown later on that the station of the plant, whether at the 

 coast or inland, has an important determining influence on the 

 buoyancy. 



In Fiji I found that almost without exception the seeds of littoral 

 plants of Caesalpinia bonducella floated both in sea-water and in fresh 

 water. On the other hand, in Hawaii the seeds of this species, 

 obtained from three typical localities removed inland from the 

 beach, sank without exception, even after drying for several months ; 

 and the only buoyant seed noted in these islands was a solitary seed 

 collected from the beach drift. In Hawaii, however, as before 

 remarked, the species is not strictly a littoral plant, occurring as it 

 does in the lower levels, but not necessarily in the vicinity of the 

 coast. In the case of seeds of littoral plants of C. bonduc in 

 Fiji, I found that sometimes all floated in sea-water and some- 

 times only a portion of them, whilst their specific weight was 

 on the whole rather greater than that of the seeds of the other 

 species. Thus, in one experiment half the seeds floated in sea- 

 water and a quarter in fresh water, whilst with seeds from another 

 locality 90 per cent, of the seeds floated in sea-water and 80 per 

 cent, in fresh-water ; and in a third set of seeds all floated in both 

 waters. 



The above experiments on Fijian seeds all relate to littoral 

 plants. In the instance, however, of the inland species from the 

 mountains of Vanua Levu, all the seeds sank in sea-water, even 

 after being kept for five years. If we follow the indications of 

 these several experiments we shall find that Caesalpinia presents 

 another illustration of the general principle established in Chapter 



