CYANOPHYCEJS 



■447 



cellulose ; the spiny resting-spores thus formed reproduce the colony by 

 division after a period of quiescence. 



With the above • exceptions the only mode of propagation in the 

 Chroococcacese is by division — repeated bipartition of the cell, which may 

 take place in one, two, or three directions. This is usually accompanied 

 by the disappearance of the separate gelatinous envelope of each indi- 

 vidual cell ; but in Glaocapsa these still remain, and as many as three 

 or four generations of families may be enclosed within the original 

 envelope, each surrounded by its own investment. In Chroococcus Nag. 

 it is not unusual for the individual cells to be entirely isolated within the 

 common envelope. In Synechococcus Nag. division takes place in one 

 direction only, and the derivative cells remain attached to one another 



Fig. 375. — Aphanoikece jnicroscopica 

 Nag. (x 70). (From nature.) 



Fig. ^-j^.—Giceothece granosa Rabh. A, gela- 

 tinous colony (magnified) ; B, cells ( x 250). 

 (After Cooke.) 



in a string ; but the attachment is very loose, and soon ceases. In 

 Merismopedia, Tetrapedia Reinsch., and Gloeochcete Lagerh. division 

 takes place in two directions, the result being the formation of a plate of 

 cells, often of great regularity. In Chroococcus, Glxocapsa, G/mothece 

 Nag., Aphanocapsa Nag., Aphanothece Nag., Microcystis, and most 

 other genera, division takes place in all three directions. In Clathrocystis 

 Henf the gelatinous envelope, which is of great extent, is broken up 

 into clathrate segments. In Ccelosphmrium Nag., a common organism 

 in bog-pools moving about with considerable rapidity, it is lobed at the 

 margin, the pseudocysts appearing like blue-green projections on the 

 surface of the globe. Chroodactylon Hansg. (Ber. Deutsch. Bot. 

 Gesell., 1885, p. 14) is distinguished by the formation of cell-families 

 branching in an arborescent manner, by its distinct cell-nucleus, and 



