96 CEYLON MARINE BIOLOGICAL REPORTS. 



in the life of the plant, or else such different conditions do not occur, but the heterophylly depends on the 

 first developed leaves being arrestment stages (" Hemmungsstadien ") of the fully developed ones. 



Are they then arrestment stages of the same kind as the primary leaves, as for instance the 

 simple leaves of Leguminosese with otherwise normal compound leaves? Yes, to a certain extent they 

 are quite analogous with them. Thus, the basal branchlets of C. dichotoma (figs. 23, 24) are undoubtedly 

 much simpler than the later dichotomous ones, and there is nothing that debars our considering 

 these simple branchlets as arrested stages of the other ones. The same may be said to apply to C. conjn- 

 ephora f. complanata (fig. IS) and G. Chemnitzia (figs. 24, 29) and other species with simpler branchlets 



at the base. 



But, on the other hand, certain reasons offer definite testimony against our explaining all the 

 differences in the development between base and top as arrestment phenomena. So, for instance, 

 C. Lessonii offers an example (fig. 11) of the branchlets at the base being arranged in many rows, i.e., 

 are more numerous at the base than higher up. The same is also the case with the /. tristichophylla of 

 C. axifolia (fig. 5) and several cupressoides forms. For in these more rows of branchlets are developed 

 at the base than higher up, and this can scarcely be characterized as an arrestment, but rather the reverse. 

 Everv case, therefore, mentioned above must not be looked upon as an arrestment stage. 



But cannot the different forms of branchlets at base and point be explained phylogenetically ? 

 That is, a Caulerpa rhizome, wliich for some cause or other has entered on a new course of development 

 as far as the form of the assimilation branches is concerned, has returned to the more primitive branch 

 form. But by reason of the exclusive propagation of GauWpa by the formation of shoots, the difference 

 between phylogeny and ontogeny is practically nil, provided the latter term is not meant to express 

 the history of the limited development of each assimilation axis (= assimilator, Reinke). 



There is scarcely any reason to consider indisputable arrestments as reminiscences of phylogenetic 

 evolution. Goebel, in his work " Vergleichende Entwicklungsgeschichte der Pflanzenorgane '' in 

 Schenk's ' Handbuch der Botanik' (III., 1), has pronounced against such an opinion. Thus on p. 261 

 he says : " Derartige Erscheinungen (=Hemmungsstadien der Laubbljitter) phylogenetisch aufzufassen, 

 dazu liegen glaube ich, kein Grund vor, ich sehe in jenen einfachen Primarblattern nur Hemmungsbil- 

 duno-en, deren Ursachen in Eigenthiimlichkeiten des Wachstums oder der Zusammensetzung em- 

 bryonaler Sposse liegt." In the cases where no objection can be raised against considering the different 

 branches as simply arrestment forms — and such cases exist, as we observed above, also in Caulerpas — 

 there is no valid reason for the hypothesis that phylogenetic phenomena has played a part, but both 

 cases are so similar and analogous tliat what is the cause of the one kind may well be supposed to be the 

 cause of the other. Experiments alone can decide the point. 



But as for the shoots in wliich tlie basal branchlets are so far from be'ng arrested that the very 

 opposite is the case, it seems that there is no other explanation possible than phylogeny. It cannot be 

 denied that the resemblance between the basal branchlets of G. dichotoma (fig. 23) and the branchlets of 

 G. Icetevirens (fig. 19) is perfect. The same holds good to almost the same extent of the corresponding 

 branchlets of G. Ghemnilzia (figs. 26, 27, 28, 29) and G. Icetevirens. And the basal branchlets of G. uvifera 

 j. planiusculn (fig. 16) are typical uvifera branchlets, just as basal branchlets of G. ta.vifolia f. tristichophylla 

 (fig. 5) are G. jalcijolia branchlets, and the basal branchlets of G. Lessonii (fig. 11) are G. cupressoides 

 branchlets. Examples of the same thing are not uncommon among the Caulerpas in general. Thus 

 G.plumarisf. i^arfowi (Weber v. Bos.se, "Monographic," p. 295, PI. XXIV., 4-6) is a form with branchlets 

 running in every direction and is to G. phimari^ as G. falcifoUa is to laxifolia. 



In this respect G. mamillosa, regarded by Madame Weber v. Bosse as a variety of G. cupressoides, 

 13 especially remarkable (Weber v. Bosse, loc. cit. p. 332, fig. 6, PI. XXVIII.). Its base is surrounded by 

 globular branchlets, which forcibly remind one of certain forms of the pedicellatce group (for instance, 

 C. lentillifera, compare fig. 6, PI. XXVIII. and fig. 2, PI. XXXIV. in Weber v. Bosse, loc. cit.). Similar 

 examples could be multiplied. These examples show clearly how the development of the branchlets may 



