102 CEYLON MARINE BIOLOGTCAL REPORtS. 



V.-ON THE GEOGRAPHICAL DISTRIBUTION OF THE CAULERPAS. 

 i. The DiSTRiBtr^rioN of thje CATitteRPAs in Ce^l6n. 

 Different Species in the North and in the South. 

 The Relationship between the different External Conditions in the North and in the South. 



In this chapter, finally, we shall deal mth the occurrence and geographical distribution of the 

 Ceylon species of CaUlefpa. 



The first question we have to answer is, How are the Ceylon Gaulerpas distributed in Ceylon ? 

 Here, of course, it is to be noted that of the twenty odd Caulerpa species in Ceylon, only relatively few, 

 about a third, occur so abundantly that they leave their stamp on the v^ej^etation as a whole. The 

 others occur only spai-sely and scattered about, and cannot be classed as plants characteristic of the 

 marine flora of Ceylon, even if they sometimes may occur quite locally in such numbers that they 

 form real associations of their own (C. verticillata, C. Imtevirens.) 



Species which occur more or less abundantly and Which— ih large districts j at least— are vfery 

 characteristic elements in the Ceylon algal flora^ are C. clavifera, uvifera, Cheinnitzia, peltata, nummularia, 

 imbricata, and possibly even sertularioides. Of these C. sertularioides occurs scattered along the Whole 

 coast, never in great masses, but alAvays rather isolated, hfemmed in between other algse. Thfe dtherS; 

 on the conttfory, occur in great quantities, and contribute in many places to give the algal vegetation 

 as a whole its stamp. Here it should be obser\'Bd that C. clavifera, nummularia, and imbricata occur 

 especially in the south-west and in the south (Colombo-Tangalla), while C. uvifera, peltata, Ghemnitzia-, 

 have a more pronounced northern distribution (Gulf of Mannar, Jaffna, Trincomalee). These 

 groups, it seems to me, confine themselves to provinces of their own to a certain extent. Here, again, 

 it is to be observed that the species that have a main distribution in common are also characterized 

 by a certain resemblance in organization. So for iirlstaiice, C. clavifera, nurhmulariti, attd even imbricata 

 are characterized by relatively short vertical axes, which gives rise to a more mat-like mode of growth 

 so that the whole assimilation system is on the same level. Ohtheother hand, both ww/ism and pe^toto, 

 as also Ghemnitzia, have lengthy vertical axes that wave in the swell, and thus they form quite a different 

 type of orgarlization. 



These differences in organization and distribution of the different species are concurrent With the 

 external conditions of algal life being so different in north and south. In southern Ceyldn the coast 

 is partly rocky and the rocks there are often fringed by splendid coral-reefs ; whereas, in the north around 

 the islands at Jaffna and at Adam's Bridge ; the shotes are shallow sand beaches with loose bottom where 

 fringing coral reefs rising to about the level of the sea are lacking. 



I have already dealt above with the differences in organization that usually accompany these different 

 external conditions, and it is very remarkable that the short-febxed clavifera, the most common CaUlerpa 

 on the coral reefs of south-west Ceylon, is replaced in the north by the closely related long-axed uvifera, 

 in the same way as G. nummularia and imbricata in the south are replaced by the allied peltata and 

 Ghemnitzia in the north. iW\ these species, as is known, are very closely related, and have also been 

 classed by Wbbbr v. Bossb as one single broad species, G. racemosa, sens. ampl. (" Monographie des 

 Caulerpas," p. 356) with a great number of sub-species, varieties, and forms. For practical as well as 

 scientific reasons I have deemed it advisable to prefer a more narrow definition of the species, but this 

 does not affect the fact that all these species and forms are genetically very closely related. With respect 

 to the fdrhi of the pinnules, G. clavifera is allied to u'vifera just as nummularia is allied to peltata ; 

 but from the point of view of organization in general we tnust group them differently, since tJien clavifera 

 and nummularia show tliemselves to be representatives for one type, uvifera-peltata for another. I 

 liave already in (lie pi'eceding given these plants as examples of the fact that also in the genus Gaulerpa 

 there is — as against wlial IIkinkk tiics to prove — a difference between morphological and adaptational 



