. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . her narrow species of Lyngbya 1 These gelatinous masses are known to the local inhabitants as Mountain Dulse, and inpast times they were rubbed into a pulp and used for purging calves (Lightfoot, 1777).- Mats of Zygnema ericetorum sometimes fulfil a similar function. 32 Myxophycese are not infrequent. In both Lyngbya and Anabtena certain of the plankton-species have become spirally coiled (fig. 19). In Aphanizomenon the fila-ments are straigh
. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . her narrow species of Lyngbya 1 These gelatinous masses are known to the local inhabitants as Mountain Dulse, and inpast times they were rubbed into a pulp and used for purging calves (Lightfoot, 1777).- Mats of Zygnema ericetorum sometimes fulfil a similar function. 32 Myxophycese are not infrequent. In both Lyngbya and Anabtena certain of the plankton-species have become spirally coiled (fig. 19). In Aphanizomenon the fila-ments are straight and densely aggregated to form floating bundles, a habitwhich is also characteristic of the marine genus Trichodesmiurn, a pinkspecies of which gives the colour to the Red Sea. Of the Coccogonesethe principal genera found in the plankton are Ccelosphserium, Gompho-sphseria, Microcystis, Ckroococcus, and Dactylvcoccopsis, the two former generasometimes occurring in such quantity as to dominate the entire plankton. The phenomena of water-bloom and the breaking of the meres aredue to the sudden and rather sporadic development of large quantities of. Fig. 19. Spirally coiled Myxophycese from the plankton. A—C, Anabasna Tatiganyikse G. ; D and E, A. circularis G. S. West; F—H, Lyngbya circuvicreta G. S. x 520. a few species of Myxophycea?, more especially certain of those which normallyoccur in the plankton of lakes and pools. The extraordinary rapidity withwhich these species multiply, with consequent discolouration of the water, isa fact which is not yet fully understood; but their disappearance, whichis often equally rapid, may be due partly to exhaustion of available food-supplies and partly to the action of toxic substances secreted by has been found by Nelson (03) that water containing water-bloom hasoften been fatal to cattle; and in this connection it is interesting to notethat horses have frequently been killed in the Gulf of Manar b
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