. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . a small disc composed of the irregularcoralliform lobes of each rhizoid. The thallus recalls that of Struvea, but the W. A. 17 258 Siph onocladiales branching has none of the regularity found in that genus. In Microdictyonthe segments of the branches are more or less of the same size, and theyform a close but irregular network. In Anadyomene the septate brancheshave long and short segments, and there are no interspaces between thebranches. Mo
. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . a small disc composed of the irregularcoralliform lobes of each rhizoid. The thallus recalls that of Struvea, but the W. A. 17 258 Siph onocladiales branching has none of the regularity found in that genus. In Microdictyonthe segments of the branches are more or less of the same size, and theyform a close but irregular network. In Anadyomene the septate brancheshave long and short segments, and there are no interspaces between thebranches. Moreover, in this genus the thallus may be clothed on both sideswith an additional layer of closely united, isodiametric branch-segments. InMicrodictyon the apices of neighbouring branches fix themselves to neigh-bouring segments and in order to strengthen their attachment a ring-likethickening of cellulose is formed at these points. In Anadyomene such athickening is also found at the apex of each segment. The chloroplasts are small polygonal plates, joined by prolongations oftheir angles in the young segments, but mostly isolated in older 1! Fig. 166. Alicrodictyon Montagneanum Gray. A, nat. size. B, a piece of the periphery ofthe thallus showing the branches, x 20. (After Montague, from Wille.) Division of the segments takes place much as in the Cladophoracese, andlentiform cells do not occur. The genera are : Anadyomene Lamouroux, 1812 [inclus. Cystodictyon Gray, 1866] ;Microdictyon Decaisne, 1832 ; Rhipidiphyllon Heydrich, 1894. They are mostly tropicaland subtropical, occurring both in shallow water and down to a depth of 50 metres. Family Cladophoracese. The septate thallus in this family consists of cylindrical or somewhattumid coanocytes forming simple or branched filaments which are neverbound together by tenacula. The different genera of the family illustrateevery condition intermediate between simple filaments, such as those ofGkxtomorpha, and the rich
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