EXERCISE 90 

 PLEUROCOCCUS THE GREEN-SLIME ALGA 



Materials. Collect pieces of green-stained bark from the north 

 sides of trees or chips of wood from fences. Moisten some of them, 

 place in a dish with a glass cover, and expose to diffuse light: Under 

 these conditions the alga will grow indefinitely. In most parts of 

 the country the material may be collected any month of the year. 



Directions for work. Examine a specimen of the dry bark 

 with naked eye and hand lens, noting the powdery appearance 

 of the masses of Pleurococcus. Examine some of the moistened 

 material with the microscope, preferably after it has had several 

 days to grow. Describe the plant. 



Determine by microscopic examination how new plants are 

 produced. 



How do you suppose Pleurococcus secures food ? Do you 

 suppose it to be an independent plant, or is it saprophytic on 

 the bark ? Experiment in the following way : Secure a piece 

 of porous earthenware from a broken flowerpot. Heat it to 

 sterilize, and place it in a dish containing about a quarter inch 

 of water. Place a small quantity of Pleurococcus on the earth- 

 enware and put the whole in a. favorable place for growth. 

 Examine from time to time for a week 'or two to determine 

 whether the plants can grow without bark or other similar 

 food material. 



References 



BERGEN and CALDWELL. Practical Botany, pp. 188-191. 

 BERGEN and CALDWELL. Introduction to Botany, pp. 221-223. 



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