376 BOTANY 



delicate filaments attached to Algae, stones, and woodwork, and forming a slimy 

 coating over them ; the filaments are composed of rod-shaped cells. Reproduction 

 is effected by ciliated swarm-cells, which originate by division from cells of the 

 filament and are set free by the swelling of the sheath (Fig. 294). The swarm- 

 cells come to rest after a time and grow into new filaments. 



Another very common form is Crenof.hrix polyspora, which consists of un- 

 branched filaments attached to the substratum, but easily broken, and can 

 accumulate hydrated oxide of iron in its sheaths. It often forms masses in the 

 cavities of water-pipes, blocking them up and rendering the water und linkable. 

 The reproduction of Crenothrix is effected by small, round, non-motile cells, which 

 arise by subdivision of the cells of a filament enclosed by its sheath. 



The numerous kinds of Sulphur Bacteria, of which Beggiatoa alba is the most 

 widely distributed, are found in sulphurous springs and at the bottom of pools 

 where sulphuretted hydrogen is being formed by decomposition of organic 

 material. The sulphur bacteria can thus live autotrophically, without organic 

 food, utilising in their metabolism salts of ammonium and carbon dioxide. These 

 bacteria oxidise sulphuretted hydrogen into sulphur, and store the latter substance 

 in the form of rounded granules within their cells, ultimately oxidising it to 

 sulphuric acid. Some Haplobacteria also belong to this physiological group 

 (cf. p. 276). 



Cklainydothrix (Leptothrix) ochracca, the so-called Iron- Bacterium, oxidises oxide 

 of iron to the hydrated oxide of iron which it accumulates in tho sheaths of its 

 filaments. It occurs in ditches and swampy places in meadows. It can thus exist 

 with only a trace of organic food, but on the other hand succeeds well without iron 

 in organic food-solutions. 



Other iron -bacteria such as Spirophyllum fcrruyineum according to LIESKE 

 are purely autotrophic. They only succeed in water containing in addition to 

 small quantities of inorganic salts some carbonate of iron. They oxidise the 

 ferrous oxide to the hydrated oxide of iron which they accumulate. This oxida- 

 tion process supplies the energy for the assimilation of carbon dioxide. 



CLASS II 

 Cyanophyeeae, Blue green Algae ( ! > 10 ) 



The Cyanophyeeae are simply organised unicellular or filamentous 

 Thallophytes of a bluish-green colour ; the cells or filaments are 

 frequently united into colonies by the gelatinous swelling of the cell 

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

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

 soil, damp rocks, or the bark of trees. Like the pure green Algae, 

 they are autotrophic. 



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 

 hlue-green pigment (phycocyau) from which the name of the class is derived, and in 

 some species also a red pigment (phycoerythrin). Tho product of assimilation 

 is glycogen. The centre of the cell is occupied by the colourless central body, 

 which corresponds to a nucleus and contains chromosome-like structures. As 

 definite inclusions of the cells may be mentioned the cyanophycin granules, 



