. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . In Mic) 0 th amnieae 301 Pleurothamnion, which is a very close ally of Gongrosira, the thallus isencrusted with lime. In Microthamnion the branches are blunt withoutthe slightest trace of attenuation, and all the species of this genus appearto be invariably free-floating and unattached. The greatest reduction ofbranches is seen in Glctsoplax, which is epiphytic on the leaves of Sphagnum. Each cell contains one parietal lobed chloroplast (rare
. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . In Mic) 0 th amnieae 301 Pleurothamnion, which is a very close ally of Gongrosira, the thallus isencrusted with lime. In Microthamnion the branches are blunt withoutthe slightest trace of attenuation, and all the species of this genus appearto be invariably free-floating and unattached. The greatest reduction ofbranches is seen in Glctsoplax, which is epiphytic on the leaves of Sphagnum. Each cell contains one parietal lobed chloroplast (rarely subdivided ?),with or without a pyrenoid. In Gongrosira and Endoderma the chloroplastmay sometimes contain from one to three pyrenoids. The zoogonidangia may be developed from almost any cell of the thallus,and in most cases are clearly differentiated by their larger size (fig. 194 C;. Fig. 194. A—C, Endoderma Wittrockii (Wille) Lagerh. A, young plant consisting of germinatingzoogonidium which has penetrated the cell-wall of a species of Ectocarpus; B, later stageshowing growth of Endoderma within the wall of the host; (7, older plant with zoogonidangia(zg). All x 425 (after Wille). D, E. Plthoplwrse G. S. West on the upper part of a spore andadjacent vegetative cell of Pithophora Clevei Wittr. ; three cells show the massive chloro-plast with a single pyrenoid, the rest in outline only. E, E. polymorpha G. S. West on thevegetative cells of Pithophora Clevei Wittr., outline of cells only. D and E, x 460. fig. 196 D and E). The zoogonidia are ovoid or ellipsoid, biciliated in somegenera (Microthamnion, Gongrosira, Chloroclonium, Leptosira, etc.), butquadriciliated in others (Sporocladus, Trichophilus, Endoderma and Pseuden-doclonium). Only one zoogonidium arises in the mother-cell in Glceoplax,2—8 in Endoderma, 4—8 in Microthamnion and Pleurothamnion, and manyin
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