CHAPTER XII 



THE CAUSES OF THE BUOYANCY OF SEEDS AND FRUITS OF 

 LITTORAL PLANTS WITH ESPECIAL REFERENCE TO THOSE 

 OF THE PACIFIC ISLANDS 



The classification of buoyant seeds and fruits.— The first group, where the cavity 

 of the seed or seedvessel is incompletely filled. — The second group, where 

 the kernel is buoyant. — The third group, where there is air-bearing tissue 

 in the seed-tests or fruit-coats. — The buoyant seeds and seedvessels of the 

 littoral plants of the British flora. — Summary. 



In the following pages I have adopted in its main features the 

 classification of buoyant seeds and fruits employed by Professor 

 Schimper in his work on the strand-flora of the Indo-Malayan 

 region. The causes of buoyancy, as he points out, are very various, 

 but they can be arranged in a few categories ; each category, how- 

 ever, usually admitting great variety within its limits. It is this 

 want of uniformity that first attracts our attention when we 

 come to study the structure of seeds and fruits from the standpoint 

 of their buoyancy. Whilst in the Pacific I went over most of the 

 field traversed by Professor Schimper in Malaya (the majority of 

 littoral plants of these regions being common to both), and as a 

 result I have added not a few plants to his original groups. 



It will be seen from the following synopsis that there are three 

 principal groups. The first group includes those seeds and fruits 

 where the buoyancy is derived from unfilled space in the seed or 

 fruit cavity. The second group comprises those seeds or fruits 

 where the floating power is due to the buoyant kernel or nucleus. 

 The third group includes those where the buoyancy arises from the 

 existence of air-bearing tissue in the coverings of the seed or 

 fruit. 



The first two groups I will term the mechanical or non-adaptive 

 groups, not only on account of the structure inducing the buoyancy, 



