. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . mus Corda, 1838 ; em. Ralfs, 1848 [inclus. RhaphidiumKtitzing, 1845 ; Schroderia Lemmermann, 1898]; Selenastrum Reinsch, 1867 ; ActinastrumLagerheim, 1882 ; Reinschiella De Toni, 1889 [ = Clostridium Reinsch, 1888]; KirchneriellaScbmidle, 1893 [inclus. Selenoderina Bohlin, 1897] ; Closteriopsis Lemmermann, 1898;Lauterborniella Schmidle, 1900 ; Desmatractum W. & G. S. West, 1902 ; DidymogenesSchmidle, 1905 ; Scenedesmus Meyen, 1829 ; Dactyloco
. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . mus Corda, 1838 ; em. Ralfs, 1848 [inclus. RhaphidiumKtitzing, 1845 ; Schroderia Lemmermann, 1898]; Selenastrum Reinsch, 1867 ; ActinastrumLagerheim, 1882 ; Reinschiella De Toni, 1889 [ = Clostridium Reinsch, 1888]; KirchneriellaScbmidle, 1893 [inclus. Selenoderina Bohlin, 1897] ; Closteriopsis Lemmermann, 1898;Lauterborniella Schmidle, 1900 ; Desmatractum W. & G. S. West, 1902 ; DidymogenesSchmidle, 1905 ; Scenedesmus Meyen, 1829 ; Dactylococcus Niigeli, 1849 (in part)[=0uracoccus Grobety, 1909]; Trtradesmus Smith, 1913. Sub-family CRUCIGENIE^E. The Algre of this small group consist of colonies of few or many cells arranged withmuch regularity in the form of a flat cells vary much in outward form, but aremostly somewhat rounded and never elongateas in the Selenastreae. Four autospores arisein each mother-cell. They are disposed in oneplane, and in certain species of Crucigenia (, fig. 132 A, and G. Tetrapedia,fig. 132 F) colonies of considerable size (128. H angvlaris (Nag.) Gay. D and E, C. quadrata Morren. F, C. Tetrapedia (Kirchu.) W. & G. S. dat. All x 520. Fig. 132. A—C, Crucigenia rect- cells) may be formed by the conversion into muciiage of the walls of the mother-cells of . successive generations. In other species ofCrucigenia (C. quadrata, C. Lauterbornii, etc.)the colonies never become very large, and con-sist mostly of from 4 to 16 cells. Even in the large colonies the cells remain in distinct groups of four, and there is alwaysa quadrate or rhomboidal space in the centre of each group, small in G. rect-angularis, G. quadrata, etc., but large in C. Lauterbornii and G. cell contains a single parietal chloroplast, often massive, and with orwithout a pyrenoid. In G. irregularis, which is known from the lakes ofNorway and the Shetlands, ^the colonies are larg
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