THE CEYLON SPECIES OF CAULERPA. 97 



be conceived as having taken place. Wliatever tlie factors were that produced them, the changes 

 (metamorphoses) proceed precisely as in other plants, in that these factors must be considered to have 

 exercised a transforming influence upon the embryonal substance in the growing point itself, and this 

 results in a successive transformation of the branchlets in some direction which then is either a direct 

 surface increase of the assimilation system (C. dichotoma, figs. 23, 24) or a transition of the assimilation 

 from several branchlets placed in many rows round a cylindrical axis to only a few but opposite rows of 

 branchlets on a flattened but broader main axis. It follows then that a study of the metamorphosis 

 of the branchlets can give us some serviceable hints for the solution of the question of the evolution of the 

 different Caulerpa species, and hence of the system and phylogeny of the whole genus. 



Thus, for instance, it seems to me that such a form as G. Icetevirens — at least as far as its assim- 

 ilation branchlets are concerned — is a very primitive type, because this form of branchlets reappeard 

 at the base of so many other forms, as C. dichotoma, Chemnitzia, and several of Weber v. Bosse's uvifera 

 and clavifera forms, which must thus be considered as younger than and derived from Icetevirens. (Cf. figs . 

 3, 8, 18, &c. , PI. XXXIII., Webek v. Bosse, Zoc. cit.). In the same way forms with the branchlets radially 

 arranged around cylindrical axes must be considered as more primitive than the bilateral forms, because 

 one often meets with axes with the branchlets at the base radially arranged, higher up bilaterally, but 

 not the other way about. Also some Caulerpas with articulated base, but for the rest with very varying 

 and different shape, show, in my opinion, that the articulation is a very old and primitive character, 

 while their form otherwise must be considered as something that has arisen in relatively recent times. 

 In any case they are undoubtedly younger than the truly articulated species of Caulerpa. 



In general, the earlier stages phylogenetically are very strongly pronounced in such plants as have 

 been developed under extreme conditions, very different in nature when compared with those under which 

 their ancestors lived. So Xerophytes, Hydrophytes, and climbing plants are often characterized by a 

 pronounced heterophylly, the explanation of which must be looked for in their phylogenetic evolution, 

 even if the plant's present mode of growth can be an explanation for its being so differently organized at 

 different periods of its life. 



As for the Caulerpas, it seems that no such sharply pronounced difference exists, with respect to 

 their external conditions of life, as may explain the cause of the different development at base and point. 

 But, in the foregoing, we have seen that the localities of the species of Caulerpa can vary not inconsider- 

 ably. So C. Icetevirens is confined to strongly exposed localities where its position is not threatened by any 

 other Caulerpa, and we have seen that its organization is an adaptation to precisely such surroundings. 

 It is highly probable that this or some similar form under altered conditions of life has given origin to 

 forms, such as dichotoma, and Chemnitzia, both of whicli could be derived from Icetevirens. In both these 

 species in the upper branchlets an increase of the assimilation surface takes place, but it is produced in 

 different ways : in dichotoma (figs. 23, 24) by the cylindrical branchlets being flattened out and becoming 

 leaf-like and, finally, bifurcated at the top; in Chemnitzia (figs. 27, 29) by the branchlets expanding 

 trumpet-like, being more sharply cut short at the top, and finally being perfectly disciform. In both 

 cases very similar results are produced, but in different ways. To this we must add that both these 

 forms, C. dichotoma and Chemnitzia, are still-water forms in comparison withC. Zce^ewVews and the gradual 

 metamorphosis of the branchlets can thus be seen in connection with the changed conditions of life, which 

 allow a surface increase of the branchlets that in C. Icetevirens is perhaps made impossible by its mode of 

 life, i.e., by the external conditions in which it grows. Therefore, of course, the external conditions 

 can very well be considered in this genus too as the factors that produce a transforming influence on the 

 growing-point by irritation, and through that the whole organization of the plant. Why the development 

 in the one case takes the direction of flattened leaf forms, and in the other of trumpet-like ones, is a 

 question that cannot, of course, be answered by deductions from the above facts. Now, at the base of 

 the branches in the derived species, branchlets are still developed of the more primitive kind which entirely 

 covered the axis system of the parent form, in the same way as Acacia seedUngs in their youth develop 

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