DIV. 1 



THALLOPHYTA 



377 



which are of proteid nature and are situated within the chromatophore. The 

 cell wall consists of cellulose and pectic substances. 



Reproduction is exclusively vegetative by cell division. In many forms resting 

 spores arise by the enlargement of single cells, the walls of which become greatly 

 thickened (Fig. 302). This process differs from that in the Bacteria. 



Just as the Bacteria are designated Fission Fungi (Schizomycetes), the Blue- 

 green Algae may be 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 eudospores of the former are unknown in the latter group. 



The simplest Cyanophyceae consist of spherical cells ; this is the case with 

 species of Chroococcus. In Gloeocapsa (Fig. 35), found on damp rocks and walls, 





v 



lefts.*? -'-' *J- " 



Fn;. 301. -4, OsciUari'i j. ,</<<< j/.s : a, terminal portion of a 

 filament : h and c, portions from the middle of a filament 

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

 B. Os<-illa,'ia Froellch.il (x 540). (After STRASBURGER.) 



FIG. 302. Nostoc Linckii. A species 

 that floats freely in water. A, 

 Filament with two heterocysts 

 (h) and a large number of spores 

 (sp) ; B, isolated spore beginning 

 to germinate ; C, young filament 

 developed from spore, (x 650. 

 After BORKET.) 



the cells remain connected together after division in a gelatinous mass, forming 

 a multicellular colony. 



The species of Oscillaria, which occur everywhere in water or on damp soil, 

 are the simplest of the filamentous forms which may be unbranched or exhibit 

 false branching (Fig. 86). The filament, which is usually provided with a thick 

 sheath, consists of similar flattened cells (Fig. 301). It can separate into pieces 

 (hormogouia), which become free owing to the pressure of the sheath, and grow 

 into new filaments. In other filamentous Cyanophyceae specially modified cells 

 with their contents degenerated occur in the filament. The significance of these 

 HETKPwOCYSTS is not yet clear. The species of Nostoc (Fig. 302), whose bead- 

 like filaments are united by the swelling of the cell walls into more or less 

 spherical gelatinous colonies living on damp soil or in water, afford an example 

 of this. 



The filamentous Cyanophyceae, especially the Oscillarieae and the hormogonia 

 of Xostoc and some related genera carry out creeping movements on a solid 



