114 A NATURALIST IN THE PACIFIC chap. 



The Third Group. 



We have here those plants where the floating-power is entirely 

 or mainly due to an air-bearing tissue in the seed-tests or fruit- 

 coats. Several of the fruits are figured in Schimper's Indo-malay- 

 ische Strand-flora, and one or two are figured in the English 

 edition of his work on Plant-Geography, p. 29. 



In the first section, where the buoyant tissue occurs at the out- 

 side or forms the periphery of the seed or fruit, are included 

 several of the most familiar of the littoral trees and shrubs of the 

 Pacific islands, such as Barringtonia speciosa, Cerbera Odollam, 

 Guettarda speciosa, Pemphis acidula, Scaivola Koenigii, Terminalia 

 katappa, and several others named in the synopsis. I cannot enter 

 into detail here, but the reader will find fuller particulars of each 

 plant in most cases in Professor Schimper's work, and in some 

 instances in my separate discussion of the plants concerned. In 

 nearly all cases we are concerned here with the fruits, and only in 

 a few cases with the seeds, as with Carapa and Pemphis acidula. 



This investigator observes that to this sub-group belong the 

 fruits and seeds usually described in systematic works as provided 

 with corky or suberous coverings ; but he points out (p. 167) that 

 the resemblance is nearly always quite superficial, and is limited to 

 colour and consistence, suberous tissue occurring in only a few 

 cases, as in the fruit-coats of Clerodendron inerme. The buoyant 

 tissues, he remarks, are often more or less ligneous, and in those 

 cases where there is no lignin reaction they resist the action of 

 sulphuric acid much more effectively than pure cellulose ; whilst 

 in their physical characters, as well as in their behaviour with 

 reagents, they differ just as much from ordinary cork. Thus, they 

 are but little elastic and often easily crumble away ; whilst in 

 large fruits, like those of Cerbera and Terminalia, they would soon 

 be stripped off entirely when subjected to the " wear-and-tear " of 

 transport by currents, if they were not traversed by numbers 

 of stout, tough fibres which hold the materials together. Where 

 the buoyant tissues are firmer, as with Clerodendron inerme and 

 Cordia subcordata, the fibrous framework is scanty or absent, 

 whilst very small seeds or fruits, like those of Tournefortia argentea 

 and Pemphis acidula, where the " wear-and-tear " would be com- 

 paratively slight, often possess no protecting fibres in the buoyant 

 tissues. 



In one or two fruits, like those of Cerbera Odollam, these 

 tissues display large intercellular spaces ; but in the majority of 



