5 TYPE STUDIES 



several hours describe the color of the water as seen by 

 transmitted lighi and by reflected light. This color is due 

 to the pigment characteristic of the blue-green algae, 

 74. Nostoc or Anabaena. 



A. Study the form and consistency of the colonies of Nostoc 

 Make a habit sketch. Cut out a small portion from a colony 

 and crush under a cover glass. Note under l.p. : 



1. The chains of cells, or filaments, imbedded in the almost 

 colorless jelly. 



2. Are the filaments branched ? continuous ? 



B. Under h.p. draw part of a filament, showing : 



1. The vegetative cells, their attachment to one another, 

 method of multiplication, and the character of the proto- 

 plasmic contents. 



2. The occasional enlarged cells, heterocysts, empty or almost 

 empty of cell contents. Two button-like plugs at the ends 

 of the heterocysts, which close what were formerly very 

 small openings into the adjacent vegetative cells. How 

 are the heterocysts distributed throughout the filaments ? 

 From what are they developed ? Their function is not well 

 known, but the filaments tend to break apart at either side 

 of these cells. How then are new filaments formed ? 



C. Material of Anabcena with resting cells, or spores, is more 

 interesting than Nostoc, and furnishes an excellent compara- 

 tive study with that type, or may be substituted for it. Study 

 the general morphology as in Nostoc, and especially the struc- 

 ture, position, and development of the resting cells. 



Reference (on the blue-green algae). Princijyles, Sees. 207-211. 



Questions. What are some of the life conditions under which 

 the blue-green algae live ? Describe the life history. How 

 may forms without differentiated resting cells, or spores (as 

 Oscillatoria), survive unfavorable seasons of drought or win- 

 ter ? In what respects is the cell structure of these plants 

 simpler than that of Spirogyra ? Compare the morphology 

 of the blue-green algae with that of the bacteria (if studied). 



