CHAPTER II. 



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. 



9. Fission-algse, — The simplest forms of the single-celled 

 green water plants are the fission-algse. In the central part 

 of the cell is the nucleus, and the whole of the protoplasm is 

 colored by the yellowish-green dye, chlorophyll. Along 

 with it, there is a blue coloring matter, so that in mass these 

 algae look bluish-green or even black- 

 ish. For this reason they are called 

 blue-green algae to distinguish them 

 from those in which only the yellow - 

 green color is present. 



10. Gelatinous colonies. — The cell- 



Avall may be thin, but commonly it is 



composed of several layers, of which 



FiG. 5. - A blue-green alga ^^6 outer are changed into mucilage. 



tfiX""!' an J''!foion£ This swclls into a transparent jelly when 



it^ified'3™Aam.-Mtl; ^et, either becoming alike throughout 



s^"'^- or showing distinct layers. When a 



number of such forms grow in company (fig. 5), this jelly-like 



material blends into a single mass in which the associated 



plants seem to be embedded. 



6 



