IN BORNEAN FORESTS [chap. 



Along the banks of this last rapid, on rocks constantly wet with 

 the spray, I found a small alga growing in profusion, and covering 

 with a violet veil the mosses and Hepaticae amongst which it 

 grew. It turned out to be a new and undescribed species of 

 Bostrychia (B. bryophila, Zan.), which has a special interest, as it 

 belongs to the Floridcce, a group of algae all but exclusively marine. 

 In Sarawak I had found another alga of this kind growing in fresh 

 water, the Delesseria Beccarii, Zan., previously mentioned, which, 

 like the above cited Bostrychia, is one of the Floridece, and belongs 

 to a genus in which not only all the other species are marine, but 

 are also the most elegant and brightly coloured of seaweeds. D. 

 Beccarii lives in the perfectly fresh and limpid waters of the Sodomak 

 stream, many feet above sea level. We have here, then, two plants 

 which may be supposed to be of marine origin, but now live in 

 fresh water far away from the sea. 1 



If the presence of such typical sea fish as sharks and rays be 

 proved in that part of the river where I found the seaweed, the coin- 

 cidence would certainly be suggestive, and offer us an example of 

 adaptation to fluviatile life of essentially marine organisms, caused, 

 perhaps, by ancient changes in the level of land in Borneo. But 

 before proceeding further on the hypothesis thus suggested, it 

 would be well not only to confirm beyond doubt the presence of 

 these sharks and rays in the Upper Rejang, but to determine the 



branch of the Sarawak river, above the rapids. Moreover, in the Sarawak 

 Gazette for 1887, p. 164, two sawfishes are mentioned as having been caught 

 at Lubok pangkalan Singhi, above Kuching, in fresh water, but within the 

 tidal influence. 



1 The fact is not new, for in 1839-48 Leprieur, an apothecary in the 

 French navy, discovered in Cayenne several small Florideae, known pre- 

 viously as exclusively marine algae, in mountain streamlets as much as fifty 

 miles inland, and at an elevation of up to 600 feet above sea level. It is 

 worthy of remark that three of them were Bostrychias of different species 

 (cf. Montagne ; Sur la station insolite de quelques Floridces dans les eaux 

 douces et courantes des ruisseaux des montagnes a la Guyane, Ann. des Sc. 

 Nat. 1850, p. 283). At Cayenne, also, in rivers within the action of the tide, 

 Leprieur found another Bostrychia, together with a small Delesseria (D. 

 Leprieurii, Mont.) which is so like the Sodomak plant that it might well be 

 looked upon as a variety of it. In Borneo I also found a Delesseria (D. 

 adnata, Zan.) and a Bostrychia (B. fulcrata, Zan.) growing on the big stems 

 of the nipa palms in waters alternately salt and fresh. These are eloquent 

 instances showing how seaweeds of two genera have become adapted gradu- 

 ally to a change of station from salt through brackish to fresh water. In 

 Bostrychia bryophylla, the adaptation to conditions of existence different from 

 the original ones would be even more extended, for it has become nearly a land 

 alga. The above mentioned facts reveal a remarkable analogy between the 

 physical conditions of the rivers of Borneo and those of Guiana ; because 

 in both countries, remote as they are from each other, a similar change in 

 the biological conditions of certain seaweeds has occurred, which can alone 

 have been caused, I think, by a similar process of adaptation, brought about, 

 no doubt, by an upheaval of the land. 



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