. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . e Autosporacese inwhich all the forms possess a definite and regular coenobium. In this case,however, the coenobium is not flat (as in Scenedesmus among the Selenastrese)but spherical or polyhedral. The three known genera are essentially differentin the grouping of the cells. In Coelastrum the cells are rounded or polygonal,adhering closely by their margins to form a hollow sphere or cube (G. cubicmn).In most species the outer surface of each
. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . e Autosporacese inwhich all the forms possess a definite and regular coenobium. In this case,however, the coenobium is not flat (as in Scenedesmus among the Selenastrese)but spherical or polyhedral. The three known genera are essentially differentin the grouping of the cells. In Coelastrum the cells are rounded or polygonal,adhering closely by their margins to form a hollow sphere or cube (G. cubicmn).In most species the outer surface of each cell is furnished with a short truncateprocess, which attains its maximum development in G. cambricum In the African species, G. compositum, the normal single cell isreplaced by a tetrad of four (vide G. S. W., 07). In C. cambrictim the cellsare joined by lateral truncate processes (fig. 133 A) and in C. reticidatum,which is mostly* a plankton-species, similar processes occur, but of a moreslender and elongate character. In BurJdllia, a genus at present only knownfrom Burma, the cells are more loosely coherent, being held in position. Fig. 133. B A, Ccclastrum cambricum Archer. B—D, Coelastrum sph&ricum Nag. Both C and Dshow the formation of daughter-ccenobia (autocolonies). All x 475. mainly by a small amount of mucus resulting from the conversion intomucilage of the wall of the original mother-cell. Each cell of the colony isprovided with a solid conical horn of large size (fig. 134 A). In Sorastrumthe cells are slightly compressed and lunate, each angle being furnished witha pair of spines (fig. 1345 and C). From the back of each cell there projectsa colourless process, and all the processes meet in the central region of thecolony where they form the facets of a small sphere. The number of cells in a colony varies from 8 to 64, but 16 is the mostfrequent number. There is a single massive chloroplast in each cell, practi-cally filling up the whole cell-c
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