SINGLE-CELLElD PLANTS ANJD COLONIES. 15 



projections (3, c, fig. 13), or is prolonged into horn-like or 

 hair-like lobes. These plants also frequently cohere into 

 colonies (/", fig. 13). In that case tooth-like projections of 

 the cell-wall may interlock. 



20. Summary. — The simplest plants consist of a single 

 cell, which is often protected by a copious mucilage. By 

 this means also the plants are often associated in colonies of 

 various forms. Among the green plants some possess in 

 addition a blue coloring matter ; others a brown. Many 

 can move about from place to place. The bacteria are de- 

 generate relatives of the blue-green algse which have lost their 

 green color, and thus their power to make their own food. 



