378 



D. Praia — The Vegetation of the Coco Group. 



No. 4, 



to introduction by means of ocean-currents. But just as we Lave seen 

 that some of the weeds may be claimed as indigenous, or at all events as 

 introduced by other than human agency, so here we find that these classes 

 pass insensibly into each other and that species which may be introduced 

 by the sea, such, as Entada scandens, Gloriosa sujoerba, JBoerhaavia repens, 

 Cocos nucifera, etc., may quite as reasonably owe their presence to a pre- 

 vious land-connection, to wind, to birds, or to involuntary or voluntaiy 

 human agency. The more doubtful instances, however, will be found 

 discussed in detail below. This group of species, however, as a whole, 

 is characterised by a general distribution which is directly affected by 

 the physiographical features of, and the currents that prevail in, the 

 surrounding seas, and is only indirectly, if at all, influenced by the con- 

 figuration of the adjacent land. 



The "coast" species have to be further subdivided in "marine" 

 and " littoral " species, and the former group, as comprising the plants 

 for which the influence of ocean-currents is most evident, will be consi- 

 dered first. Only one Phanerogam belongs to this class; this species, 

 Gymodocea ciliata, is however almost the most plentiful, the only other 

 common species being Sargassum ilicifoUuin ; all the others are veiy incon- 

 spicuous, being few in number, small in size, and scantily represented. 



The following table gives at once a list of, and indicates the marine 

 distribution for, these species ; for six of them, as the general list shews, 

 this is, as regards the Algce, only approximate. 



Table XIII. Distribution of the " Marine " species present in the Coco 



Group. 



Species. 



'-I3 

 1 

 < 



O 



.2 



-3 

 a 



6 



eg 



'3 



Oh 



Species. 



_d 



c 

 < 



a 



Q) 

 O 



O 

 a 



'5 



Gymodocea ciliafca 





X 





Gelidium corneum 



X 



X 



X 



Sargassnm ilicifolinm 



X 



X 



X 



Caulerpa clavifera 



X 



< 



X 



Turbinaria ornata 



— 



X 



— 



Caulerpa plamaria 



- 



X 



— 



Padina pavonia 



X 



X 



X 



Valonia fastigiata 



— 



X 



X 



Dicfcyofca diohotoma 



X 



X 



X 



Valonia confervoides 



— 



X 



— 



Lithothamnion polymorphum ... 



X 



X 



— 



Halimeda Opantia 



X 



X 



X 



Acanthophora Thierii 



X 



X 



X 



Siphonocladus ? filiformia 



— 



X 



— 



Jania tenella 



— 



X 



— 



Vaucheria sp. 



— 



X 



— 



Gracilaria crassa 



— 



X 



— 



Calothi-ix pnlvinata 



X 



X 



X 



Nearly one-half of the species are cosmopolitan in tropical seas ; 

 probably some of the six of which the distribution is not accurately 

 ascertained are also cosmopolitan. One species appears to extend 



