GloeocystesR 



189 



cells is in two directions in a plane such that the colony becomes a flat 

 expansion. The majority of the divisions are in one direction and the cells 

 in consequence assume a seriate arrangement. The chloroplast is parietal 

 and massive, with or without a pyrenoid. 



The only genera are: Palmophi/Hitm Kiitzing, 1845; Collinsiella Sctchell & Gardner, 

 1903. Both are freshwater genera attached to sul nnerged stones. 



Sub-family GUEOCYSTE/E. In this sub-family the plants consist of small 

 colonies of cells each of which is surrounded by a lamellose mucous invest- 

 ment. The concentric coats of mucus can be distinguished either round 

 each individual cell or round a small group of daughter-cells. The greatest 

 lamellation of the enveloping jelly is seen in Asterococcus, in which the 

 envelope round a single cell (25 30 /n in diameter) may attain a diameter 

 of 180/n. In Palmodictyon (fig. 1155) the groups of cells with their sur- 



Fig. 115. A, four-celled colony of Glaiotfenium Loitlesbergerianum Haiisg., x 430, showing black 

 deposit in mucilaginous envelope. B, a small portion of a branched colony of Palmodictyon 

 viride Ku'tz., x 430. C, colony of Hormotila tropica G. S. West, x 430. 



rounding integuments are disposed in more or less cylindrical threads which 

 branch and anastomose with each other; and in Hormotila the cells are 

 usually aggregated to form a thin stratum, the secretion of mucus being 

 mostly on one side so that each cell becomes possessed of a lamellate mucous 

 stalk (fig. 115 C). 



The chloroplast is in most cases parietal and massive, with or without a 

 pyrenoid; but in Asterococcus (Scherffel, '08 A) there is an axile chloroplast 

 with numerous radiating outgrowths, each of which becomes slightly ex- 

 panded against the inner side of the cell-wall. There is a central pyrenoid, 

 numerous starch-grains often fill the cells, oil is stored in small drops in the 

 cytoplasm, and two contractile vacuoles and a conspicuous pigment-spot occur. 

 Increase of the cells takes place by successive divisions of the mother-cell, 



