174 A NATURALIST IN THE PACIFIC chap. 



seeds from four different inland localities gave 13 as the mean per- 

 centage of buoyant seeds.) 



As in the case of Entada scandens, there is a rather fine adjust- 

 ment between the mean specific weight of seeds and the density 

 of water. If we place a number of the buoyant seeds in sea-water 

 and begin to lower the density, some of the seeds will at once 

 commence to float heavily and afterwards sink ; and when the 

 density has been lowered to approximately that of fresh water, 

 usually about a third will be found at the bottom of the vessel. 

 Out of 100 coast seeds, 70 will, as a rule, float in the sea and about 

 47 in the river ; whilst of the same number of inland seeds, 13 on 

 the average will float in sea-water and 8 or 9 in fresh water. The 

 bearing of facts of this kind is especially discussed in Chapter X. 



Coming to the causes of the floating-power of the seeds, we find 

 that with the buoyant seeds the kernel floats, whilst with the non- 

 buoyant seeds it sinks, the seed-tests in neither case possessing any 

 floating-power. In this respect, therefore, the seeds of Afzelia 

 bijuga belong, with the seeds of some other Leguminous littoral 

 plants of the Pacific islands, such as Canavalia obtusifolia, Eryth- 

 rina indica, and Sophora tomentosa, to the second section of the 

 second non-adaptive group of buoyant seeds (page 107). 

 But though we can in a measure explain the cause of the 

 buoyancy, we are still ignorant of the manner in which the differ- 

 ence in the buoyant behaviour of coast and inland seeds has been 

 brought about. It is possible that this may be connected with 

 another difference between the coast and inland seeds, the latter 

 being markedly smaller, and it is noteworthy that in my experi- 

 ments the smaller seeds were generally those that sank. (Whilst 

 the inland seeds averaged between f^ and i inch, or 20 to 25 mm., 

 in greatest diameter, 12 to 16 being required to make an ounce, 

 the Coast seeds measured i to i-j^ inch, or 25 to 30 mm., and only 

 10 or II were needed to weigh an ounce.) 



There can be no question that the seeds are at times trans- 

 ported by the currents over wide tracts of sea, and this no doubt 

 explains the occurrence of Afzelia bijuga in oceanic islands. They 

 may be usually seen lying free in numbers on the ground beneath 

 the tree or else still inclosed in the fallen dehiscing and decaying 

 pods ; and they might be swept sometimes into the sea or washed 

 down into an adjacent stream. They thus came under my notice 

 amongst the stranded beach drift at the mouths of estuaries in Fiji, 

 But it is remarkable that the seeds have not apparently been 

 recorded from the beach drift of other tropical regions. Penzig 



