338 



BOTANY 



frequently united into colonies by the gelatinous swelling of the cell 

 walls. The numerous species, which are distributed over the earth, 



FIG. 261. Gloeocapsa polydtrmatica. 

 A, In process of division ; B, to 

 the left, shortly after division ; 

 C, a later stage, (x 540.) 



Fio. 262. A, Oscittaria pHnceps: a, terminal portion of a 

 filament ; b, portions from the middle of a filament, 

 properly fixed and stained ; t, cells in division (x 1080). 

 B, Oscillaria Froclichii (x 540). 



live in water, or form gelatinous or filamentous growths on damp 

 soil, damp rocks, or the bark of trees. 



The protoplast of each cell possesses a peripheral chromatophore of the form of 

 a hollow cylinder or hollow sphere ; in addition to 

 chlorophyll this contains a blue - green pigment 

 phycocyan from which the name of the class is 

 derived. The product of assimilation is glycogen. 

 The centre of the cell is occupied by the colourless 

 central body, which corresponds to a nucleus and 

 in vegetative cells is in a condition of continuous 

 mitotic division. As definite inclusions of the cells 

 may be mentioned the cyanophycin granules, which 

 serve as reserve material and are situated in the 

 neighbourhood of the transverse septa or within 

 the chromatophore, and the mucilage spheres which 

 appear in close proximity to the nucleus. Chitin 

 has been shown to be present in the cell wall. 



Reproduction is exclusively vegetative by cell 

 division. In many forms resting spores are formed 

 by the enlargement of single cells, the walls of 



which become greatly thickened (Fie. 263). Resting 

 ment with two heterocysts (h) , . 



andalargenumberof spores(<i); nuclel *** P resent ln these S P reS ' 

 B, isolated spore beginning to J us t as the Bacteria are designated Fission- 

 germinate; C, young filament Fungi (Schizomycetes), the Blue-green Algae may 

 developed from spore. (After jj e termed Fission-Algae (Schizophyceae), since the 

 reproduction of both depends on fission. The two 



groups would form the class of fission plants Schizophyta. The Bacteria and the 

 Cyanophyceae have much in common, but the cilia and endospores of the former 



A 



Fio. 263. Nostoc LincUi. 



