SCHIZOPHYTA. 



23 



tinguished from the ordinary vegetative cells (Fig. 22 Ji) by their 

 larger size, yellow colour, and poverty of contents. Branching 

 sometimes occurs and is either true or spurious. 



FIG. 16. Microcoleus lyngbyanus : a portion of a filament, the thick sheath encloses only 

 one cell-chain ; in one place a cell is drawn out by the movement of the cell-chain; I the 

 cell-chain has divided into two parts (" hormongonia ") which commence to separate 

 from each other. 



The cell-chain in the spurious branching divides into two parts, 

 of which either one or both grow beyond the place of division 

 (Fig. 18) and often out to both sides (e.g. Scytonema\ the divisions 

 however, always take place transversely to the longitudinal 

 direction of the cell-chain. In the true branching a cell elon- 

 gates in the direction transverse to the cell-chain, and the division 

 then takes place nearly at right angles to the former direction 

 (Sirosiphoniacece). 



FIG. 19. Cylindrospevmum mojits : a resting akinete with heterocyst ; l-d germinating 

 stages of a resting akinete ; e filament with two heterocysts and the formation of new 

 akinetes ; / part of a filament with a heterocyst, and mature resting akinete. 



Cilia are wanting, but the filaments are sometimes self-motile 

 (e.g. hormogonia in Nostoc} and many partly turn round their axes, 

 partly slide forward or backward (Oscillaria) . 



Reproduction takes place by spores and hormogonia in addition 



