76 LABORATORY AND FIELD EXERCISES 



3. Reproduction. Study the method of reproduction outlined 



and illustrated (Fig. 115) for Protococcus in the text. 



a. Observe three or four stages in reproduction from your 



mounts of Protococcus. Is this a vegetative or a 

 sexual method of reproduction ? Is it a rapid or a 

 slow method ? What becomes of the loose colonies 

 formed by reproduction when the plants are exposed 

 on bark, boards, or stones ? 



b. Sketch three or four stages in the reproduction of Pro- 



tococcus, beginning with a single-celled plant. 



4. Dissemination. How does Protococcus spread from tree 



to tree or from any one habitat to another ? How does 

 it form a large incrustation from the first few cells in 

 a new habitat ? Why does it usually occur on the 

 north side of trees and fences ? Why is it more abun- 

 dant on rough than 011 smooth surfaces ? 



5. Nutrition. What is the source of the water, gases, and 



salts which constitute the raw food materials for Pro- 

 tococcus plants ? How are these materials absorbed ? 

 Are they made into foods and used by Protococcus as 

 they are in a tree or a geranium plant? Be able to 

 indicate the income and outgo of food materials and 

 wastes in Protococcus plants. 



6. Summary and discussion. Discuss briefly in your notes 



the mam points indicated above concerning the struc- 

 ture, reproduction, dissemination, and nutrition of 

 Protococcus. 



CHLA MYDOMONA S 



If Chlamydomonas is available for study, compare it with 

 Protococcus in structure, reproduction, and dissemination. Note 

 particularly the rate and mode of movements in active Clilamy- 

 domonas plants. The brick-red eyespot and the cup-shaped 

 chloroplast may be observed in forms which have come to rest. 



