. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . or blackrocks. At the end of May the Alga3 beginto be discoloured with the intense heat, andthe large patches begin to dry and peel the rocks reappear in their naturalgrey or brownish-grey colour, and remainthus through the hot season until thebeginning of the next rains (Welwitsch,1868; W. & G. S. W., 97). In coldlatitudes and at high altitudes Myxophyceaeof all kinds can withstand prolonged andrepeated freezing. In the Antarctic in
. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . or blackrocks. At the end of May the Alga3 beginto be discoloured with the intense heat, andthe large patches begin to dry and peel the rocks reappear in their naturalgrey or brownish-grey colour, and remainthus through the hot season until thebeginning of the next rains (Welwitsch,1868; W. & G. S. W., 97). In coldlatitudes and at high altitudes Myxophyceaeof all kinds can withstand prolonged andrepeated freezing. In the Antarctic in thevicinity of Ross Island and South VictoriaLand (lat. 77°32S. to lat. 77°45/S.) Blue-green Algae, form the dominant vegetationof the pools and lakes, which is remark-able considering the severity of theclimate. The growing season only lastsfor about four weeks, and during the re-maining part of the year the Algse arecompletely frozen. Sometimes they passseveral years in this frozen state, without being once thawed, and yet 1 According to Phillips the spores of Oscillatoria will germinate after a resting-period of ayear and a half. W. A. 2. Fig. 20. Gomontiella subtubulosa Teo-doresco. A, ventral view of filament;B, transverse section; C, opticallongitudinal section ; D, ventral viewof a longer and more twisted x 580 (after Teodoresco). 34 Myxophycex the plants survive and resume activity as soon as circumstances are suffi-ciently favourable (W. & G. S. W., 11; and Fritsch, 12). The genus Gomontiella exhibits a unique adaptation against plant is a member of the Oscillatoriacea? in which the filaments aregreatly flattened and at the same time rolled to form a capillary tube (fig. 20).The plants occur in shallow water-holes which are liable to becometemporarily dry, but little evaporation can take place from the ends of thetube-like plant, and thus the filament retains its own water supply and veryrarely becomes completely desiccated. (Teodo
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