. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . nding generations after development of girdle-bands; s, sj and s2 refer tosemicells, and g, g1 and g-2 to girdle bands of successive generations. Ill and IV, Closteriumlurijidnm Ehrenb. var. giganteum Nordst., xl200; IV, surface view of the median part ofthe cell; III, longitudinal section of same; r, the ring-furrow in the middle of the cell;t and t, short transverse segments of cell-wall, resulting from cell-divisions, showing thebevelled s
. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . nding generations after development of girdle-bands; s, sj and s2 refer tosemicells, and g, g1 and g-2 to girdle bands of successive generations. Ill and IV, Closteriumlurijidnm Ehrenb. var. giganteum Nordst., xl200; IV, surface view of the median part ofthe cell; III, longitudinal section of same; r, the ring-furrow in the middle of the cell;t and t, short transverse segments of cell-wall, resulting from cell-divisions, showing thebevelled sutures. (All modified from LiitkemiUler.) 02). The girdle-bands (or intercalary bands) are not comparable with thoseof Diatoms (consult p. 119). Asexual reproduction takes place very occasionally by the formation ofaplanospores (fig. 233 E—G and H—J). Desmidiacese 371 These have been observed in Spondylosjum nitens (Wallich) Arch. (Wallich, 60 ;Turner, 93), Closterium Cornu Ehrenb. (Lagerheim, 86), Hyalotheca neglecta Racib.(W. & G. S. W., 98), H. dissiliens (Sm.) Breb. (W. & G. S. W., 07) and Cosmariumbioculatwm Breb. (Nieuwlaud, 09).. Fig. 233. Zygospores aiid aplanospores of Desmids. A—G, Hyalotheca dissiliens (Sin.) Breb.;A, vegetative filament; B, end view of cell; G and D, zygospores, x 338; E—G, aplano-spores, x 468. H—K, H. neglecta Eacib. ; H—J, aplanospores (a); K, zygospore, x , Micrasterias denticulata Breb., x 100. M, Euastrum oblongum (Grev.) Ealfs, x , Cosmarium bioculatum Breb., x 425. 0, Penium suboctangulare W. West, x , Arthrodesmus octocornis Ehrenb., 425. Q, Staurastrum granulosum (Ehrenb.) Ealfs, x 468. Sexual reproduction of a low, and probably degenerate, type occurs by theconjugation of two individual cells and the fusion of two large equal gametesto form a zygospore. The conjugation is similar to that in the Zygnemacese 24—2 372 Conjugate and with the solitary exception of Desmidium cylindricum, there is no definiteco
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