THALLOPHYTA 



7 



Some are unicellular, occurring either isolated or in colonies ; others are 

 filamentous, a large number of the filaments being generally aggregated to 

 form either a stratum or a definite colony. 



Among the Blue-Green Algae commonly met with in South Africa, one 

 of the most striking is a species of Nostoc (Plate 2, Fig. M 1,2, 3). This 

 consists of nearly spherical blue-green colonies, each made up of countless 

 numbers of minute filaments embedded in a mass of jelly. Each filament 

 consists of a row of barrel-shaped cells, with here and there a larger cell 

 interposed, which is called a hetevocyst. The commonest method of 

 reproduction is by the breaking up of the filaments at the heterocysts into 

 shorter filaments, which then regain their former size by cell-division and 

 growth. Less commonly some of the cells of certain filaments become 

 converted into spores. 



Some other species of Nostoc will be mentioned under Encephalartos 

 (Vol. 1 page 94) and Gunnera (Vol. 11). 



IV. FLAGELLATAE. 



The Flagellatae are a group of minute and very lowly organisms, all 

 unicellular and with characters intermediate between those of plants and 



Fig. 3. Euglena gracilis Klebs A. 

 Form with green chromatophores 

 (ch); «, nucleus; v, vacuole with 

 eye spot (red) ; g, flagellum. 

 B. Division of cyst into 4 

 daughter-cells, 1000/1 (After 

 Zumstein). C-F. Euglena 



sanguinea (After G. Haase), 

 1 690/ 1. C and D two ga- 

 metes. E. Young zygote with 

 2 nuclei and 4 chromatophores. 

 F. Zygote after fusion of 

 nuclei. 



animals. It is not necessary to discuss the question to which kingdom 

 they may be more conveniently relegated, as they probably constitute the 

 starting point from which on the one hand the main groups of Thallophyta, 

 on the other the Protozoa, have been derived. 



Each cell (Fig. 3) is bounded by a protoplasmic membrane, in which 



