Fig. 169 Cyanophyceae. A-C, geminate branching in Scytonema 

 pseudoguyanense (A, x 470, B, C, x 340). D, false branching in 

 Calothrix ramosa ( x 570). E, false branching in Scytonema pseudo- 

 guyanense showing branch sheath (Jbs) tenninating at heterocyst. 

 ps = parent sheath, J = dead cell ( x 590). F, hormogones emerging 

 from parent sheath in 5. guyanense ( x 750). (After Bharadwaja.) 



tween two heterocysts or else adjoining one as a result of the de- 

 generation of an intercalary cell. The intercalary growth results in 

 strong pressure being apphed to the sheath, which finally ruptures 

 so that the trichome forms a loop outside (Fig. 169, A-c). Further 

 growth causes this loop to break, thus producing twin branches, 

 one or both of which may subsequently proceed to additional 

 growth, the branch sheaths extending back into the parent sheath 

 (Fig. 169, e). False branching may also be initiated by degeneration 

 of a vegetative cell or heterocyst and subsequent growth of the two 

 filaments on either side. 



* RivULARiACEAE : i^/z^w/ana (rivulus, a small brook). Fig. 170 



The colonies form spherical, hemispherical or irregular gela- 

 tinous masses that are attached to plants or stones or they occur on 

 the soil, those of i^. atra being especially frequent on salt marshes. 

 Each colony contains numerous radiating filaments with repeated 

 false branching, each branch terminating in a colourless hair. With 

 the production of mucilage the 'branches' become displaced and 

 their origin is not easy to see. The individual sheaths can be seen 



289 



