CHAPTER I. 



SINGLE-CELLED PLANTS AND COLONIES. 



In the lakes and pools, in ditches and slow streams, on 

 the surface of damp rocks and wood, may be found many 

 sorts of microscopic plants, whose entire body is merely a 

 single cell. 



Blue-green algae. 



11. Fission-algse. — The simplest forms of these, the fission- 

 algae, have the protoplasm only slightly differentiated. The 

 central part becomes the nucleus, while the whole of the 

 remaining protoplasm is colored by the chlorophyll and a 

 blue coloring matter called phycocvanin, so that in mass these 

 algae look bluish-green or even blackish. For this reason 

 they are called blue-green algae to distinguish them from those 

 in which only the yellow-green of chlorophyll is present. 



12. Gelatinous colonies. — The cell-wall may be a thin 

 sheet of cellulose, but commonly it is 

 composed of several layers, of which 

 the outer are changed into mucilage. 

 This swells into a transparent jelly 

 when wet, either becoming homo- 

 geneous or showing distinct stratifica- 

 tion. When a number of such forms 

 grow in company (fig. 12), this 

 jelly-like material blends into a single 



plants seems to be em- 



Fig. 12— A blue-preen aljra 

 (Gl(roca/>sa<. Single indi- 

 viduals, A, and colonies 



\S' E) r °a va r ous wf s associated 



Magnified 300 diam. — After 



Sachs - bedded. 



13. Gelatinous filament-colonies. — In other cases, instead 

 of being associated only by the adhesion of the mucilaginous 

 portion of the cell-wall, the cells, still practically inde- 

 pendent the one of the other, remain connected by the 



