. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . B. Trichophoreie. Trichomes markedly attenuated towards one or bothextremities, which are often drawn out into hair-like points. Fam. Rivulariaceae. In this family the trichomes are attenuated from the baseupwards and are often piliferous. In all except a few cases there is a single heterocyst atthe base. There is a well-marked tubular sheath, gelatinous or membranous, and oftenstrongly lamellose. There is a prominent false branching in the g

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. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . B. Trichophoreie. Trichomes markedly attenuated towards one or bothextremities, which are often drawn out into hair-like points. Fam. Rivulariaceae. In this family the trichomes are attenuated from the baseupwards and are often piliferous. In all except a few cases there is a single heterocyst atthe base. There is a well-marked tubular sheath, gelatinous or membranous, and oftenstrongly lamellose. There is a prominent false branching in the genus Dichothnx,accompanied by a conspicuous fusion of sheaths. The filaments of Culotliriv generally Rivulariacex 45 form an expanded stratum on wet rocks and submerged stones (tig. 35). In Rimdaria thefilaments are disposed to form subglobose or hemispherical, attached masses, sometimes. Fig. 34. A and B, Stigonema miniitum, Hass.; A, x 100; B, x 440. C—fi, St. oceUatum(Dillw.)Thur.; C, xlOO; D &m\ E, x 400. ft, heterocyst.

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