. The algae. Algae. 320 THE ALGAE thesis only involves the loss of the gametophyte generation. Against the first hypothesis is the fact that very few members of the Ecto- carpaceae are known to be haplonts, and in one good case, E. virescens, the parthenogenetic development of the eggs suggests degeneration rather than primitiveness. The general weight of evi- dence would appear to be in favour of isomorphic alternation as the primitive Phaeophycean condition. Schemes A and B represent two sUghtly different views of evolu- tionary development within the Phaeophyceae, in both cases starting fro
. The algae. Algae. 320 THE ALGAE thesis only involves the loss of the gametophyte generation. Against the first hypothesis is the fact that very few members of the Ecto- carpaceae are known to be haplonts, and in one good case, E. virescens, the parthenogenetic development of the eggs suggests degeneration rather than primitiveness. The general weight of evi- dence would appear to be in favour of isomorphic alternation as the primitive Phaeophycean condition. Schemes A and B represent two sUghtly different views of evolu- tionary development within the Phaeophyceae, in both cases starting from a simple branched filamentous ancestor with iso- morphic alternation. Which of these two schemes is accepted de- pends very largely upon the view taken about the origin of the Fucales and Laminariales. The origin of the Rhodophyceae presents almost as many diffi- culties as that of the Phaeophyceae. On one hand they may have Oogamy __Dictyotales Fucales 1 -^ 4o ^ T Tilopteridales \ / Anisogamy V Cutleriales J / Laminariales A c_u-^«i^^:,Ur \ ^ Sporochnales / ?/ ^ / Desmarestiales I / Advanced Chordariales Sphacelariales Isogamy reduced Ectocarpales / Dictyosiphonales 1 Ectocarpales Primitive Ectocarpales ISOGENERATAE HETEROGENERATAE Scheme A Dictyotales Sphacelariales Haplostichineae A Sporochnales Desmarestiales Cutleriales-<. Polystichineae A Laminariales Fucales Tilopteridales -<- ISOGENERATAE. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Chapman, V. J. (Valentine Jackson), 1910-. London, Macmillan; New York, St. Martin's Press
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Keywords: ., bo, bookcentury1900, bookcollectionbiodiversity, booksubjectalgae
