342 THE SIMPLEST PLANTS 



SUMMARY 



Both pleurococcus and spirogyra are called algae, and 

 each is typical of many other plants of the same kind. 

 Our chief interests in them are that they are adapted to 

 life in the water from which they obtain most of their food 

 and that each cell is capable of carrying on all the life 

 processes for itself. Plants like pleurococcus are called 

 unicellular ; those like spirogyra, which consist of many 

 cells joined end to end thus forming a strand, are called 

 filamentous algce. Pleurococcus is found on old buildings, 

 fences, posts, rocks, and on the bark of trees. It shows 

 more plainly in wet weather than in dry, for then it is 

 growing. Spirogyra grows in running water, attached to 

 objects on the bottom, or floats in masses on the surface 

 of ponds, ditches, and sluggish streams. Neither of these 

 plants has any economic value. 



Algae are simple plants which grow in water or in moist 

 places. Fresh water algae are usually small. Algae illus- 

 trate how a plant cell carries on the life processes. The 

 cell is the unit of plant structure, and plant cells are 

 similar to animal cells in all essential respects. 



QUESTIONS 



What is a cell? Compare plant with animal cells. Explain the 

 process of conjugation. In what respects is the formation of a zygospore 

 similar to the process of fertilization in the bean ? 



REFERENCES 



Atkinson, High School Botany. 

 Bennett and Murray, Cryptogamic Botany. 

 Bergen and Caldwell, Botany. 

 Leavitt, Outlines of Botany. 



