86 TYPE STUDIES 



several hours describe the color of the water as seen by 

 transmitted light 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 ? 

 Trom 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 comparar 

 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-gre^n algae). Principles; 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). 



