446 



PROTOPHYTA 



organism with blue-green endochrome which he regards as the swarm- 

 cell condition of a phycochromaceous alga which occurs normally in a 

 filamentous form, probably as Oscillaria tenuis (Ag.) or O. Frolichii 



(Ktz.). 



LITERATURE. 



Fresenius Ueb. d. Ban u. d. Leben d. Oscillarieen, 1845. 

 Braun Bot. Zeit., 1852, p. 395. 



Bornet and Thuret Notes Algol., fasc. I, pp. iii.-iv.' ; and fasc. 2, pp. 132-135. 

 Zukal Oesterr. Bot. Zeitschr., 1880, p. n. 



Hansgirg Oesterr. Bot. Zeitschr., 1884, pp. 313 et seq. ; and Ber. Deutsch. Bot. 

 Gesell., 1885, p. 14. 



Sub-class 2 and ORDER 5. Chroococcacese. 



The Chroococcaceae share with the Schizomycetes the distinction 

 of being among the lowest forms of vegetable life. The separate 

 cells are always microscopic, and are filled with a blue-green or violet 

 endochrome which owes its colour to the phycocyanin dissolved in the 

 cell-sap ; they contain neither distinct chlorophyll-grains nor starch, nor, 

 except in Chroodactylon (Hansg.), a distinct nucleus. The cells are either 

 isolated, or are more often connected together 

 into colonies by a mucus formed from the 

 disintegration of the outer layers of the cell- 

 wall ; they are never united into a filament. 

 This gelatinous envelope is either colourless and 

 hyaline, or of a blue, brown, or olive colour, 

 and is often strongly lamellated. In Chroo- 

 coccus (Nag.) it is homogeneous and capable of 

 swelling greatly; in Glceocapsa (Ktz.) it is com- 

 posed of two successive layers, and becomes 

 eventually, in some species, crustaceous, and of 

 a very dark brown or even black colour. 1 he 



. . 7 . , j j 



internal pseudocysts or gonids are never endowed 

 with cilia, as in some Protococcaceae, and are 



usually quiescent ; but in Microcystis (Ktz.) they have a constant 

 ' swarming ' motion within the hyaline envelope. The entire organism 

 has usually a power of slow spontaneous motion. Multiplication by 

 swarm-spores or zoospores is unknown except in the doubtful case 

 of Merismopedia (Mey.) (Goebel, 'Outlines of Classification,' p. 22). 

 Resting-spores or cysts (akinetes) are formed in Glceocapsa by the 

 cells of which a colony is composed investing themselves, while still 

 within their common gelatinous envelope, in a rough or spiny coat of 



FIG. 374.-Stages in the de- 



veiopment of ckroococcus 



turgidus Nag. (greatly mag- 



nified). (After Reinke.) 



