90 



PLANT LIFE. 



hormogones escape from the sheath enclosing the filament, 

 and serve as the starting-point of new individuals. Motile 

 reproductive cells Or zoospores are, with a few doubtful 

 exceptions, absent. The simplest forms, as Glceocapsa and 



-J. 



Fig. 17. — (x 540). GliBocafsa folydermaiica, a minute fresh-water alga, 

 showing stages in the formation of a colony or cell-family {cosnobium). 

 In A the protoplasm (shaded portion) of an individual is becoming 

 elliptical with a slight constriction in the centre, preparatory to dividing 

 into two individuals, the thiclc mucilaginous cell-wall is lamellated. In 

 B the division is complete, and the two daughter-cells or individuals 

 have become elongated, preparatory to further division. In C the four 

 individuals forming the colony are spherical and in the vegetative 

 condition. (From Strasburger.) 



Chroococcus, are unicellular, and usually form colonies 

 enclosed in a gelatinous envelope formed by the gellifica- 

 tion of the outer layers of the cell-wall ; this envelope is 

 frequently lamellated or composed of several layers. In 

 the genus Nostoc, common on damp ground and in bog- 

 pools under the form of bluish-green or dingy violet 

 gelatinous masses of variable size, the chlorophyll-bearing 

 portion forms a filament which at first sight resembles a 

 chain of cells ; the component portions however differ from 

 true cells in the extremely thin cell-wall being inseparable 

 from the protoplasm, which it also closely resembles in its 

 chemical reactions. These primitive cells differ from those 

 of GlcBocapsa in being arranged in a moniliform or necklace- 

 like chain. The protoplasm of all the cells composing the 



