. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . MycotetraedronHansgirg, 1890 (fig. 127 (7) and Chionaster Wille, 1903 (fig. 127 A and B). Chodat (1895) states nomen ineptum ob affiue Tetracera Dilleuiacearum. Selenastrese 201 Sub-family SELENASTRESE. The Alga? of this group are characterizedby the elongation of the cells, which are often very narrow with the ex-tremities attenuated to fine points. They are frequently lunate or arcuate,and may be solitary or associated to form colonies ofte
. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . MycotetraedronHansgirg, 1890 (fig. 127 (7) and Chionaster Wille, 1903 (fig. 127 A and B). Chodat (1895) states nomen ineptum ob affiue Tetracera Dilleuiacearum. Selenastrese 201 Sub-family SELENASTRESE. The Alga? of this group are characterizedby the elongation of the cells, which are often very narrow with the ex-tremities attenuated to fine points. They are frequently lunate or arcuate,and may be solitary or associated to form colonies often of a more or lessfragile character (Actinastrum, fig. 130 .A and B\ Selenastrum, fig. 131), thecells in some instances being held in position only by an envelope of mucus(Ankistrodesmus Pfitzeri, Kirclineriella, Elakatothrix). In many species ofAnkistrodesmus, in Dactylococcus, Closteriopsis, and most forms of Scenedesmusthere is no enveloping mucus. The cell-wall is firm but delicate. Each cellcontains a large elongated chloroplast which often fills almost the entire some forms pyrenoids do not occur, but in others one or more pyrenoids. aut. Fig. 128. A, Scenedesmus oblh/uus (Turp.) Kiitz. B, the culture-state of S. obliquus formerlyknown as Dactylococcus infusionum Nag. C, S. bijugatus (Turp.) Kiitz. D—F, S. quadri-cauda (Turp.) Breb. G, S. quadricauda var. horridus Eirchn. H, S. quadricauda W. & G. S. West. I—K, S. denticulatus Lagerh. var. line arts Hansg. L, S. spicatusW. & G. S. West. All x 520. aut, autocolonies. are invariably present. In the ubiquitous species Ankistrodesmus falcatus,and especially in its var. acicularis, pyrenoids may be present in some indi-viduals but not in others (fig. 129 B). Scenedesmus and Tetradesmus arethe only genera with a definite coenobium; in the former the cells arearranged side by side (with their long axes parallel) in one plane, and inthe latter side by side in two planes (Smith, 13). % Reproduction ta
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