22 NOSTOC. 



MINUTE STRUCTURE. 



1. Mount a small piece of the colony, and under low power 

 observe the almost colorless granular jelly in which are 

 seen chains of cells. 



2. Note whether there is any regularity in the arrangement 

 of the filaments. 



3. Under high power study a filament to determine: 



a. The form and number of cells which compose it. 



b. The attachment of the cells one to another. 



c. The form, position, and number of peculiar enlarged 

 cells, the heterocysts. 



d. The relation of the heterocyst to reproduction of the 

 filaments. 



e. The structure of a single cell. 



4. Compare several plants with reference to the points sug- 

 gested in 3. 



5. Draw in detail one or two representative filaments. 



ANNOTATIONS. 



The individual cell of a Nostoc plant is oblong, has a 

 distinct cell-wall and granular bluish-green protoplasm. 

 Nuclei are not easily demonstrated, and until recently 

 their existence had been questioned. Each cell is proba- 

 bly independent of its neighbors in nutritive work, though 

 doubtless association with them assists it. It seems 

 probable that Nostoc plants absorb some food (organic 

 matter) from the water or earth, for they grow only in 

 situations where this is present. This would remove 

 the necessity of so much food- making by these plants, 

 and would accord with the small amount of chlorophyll in 

 the cells. 



While in Pleurococcus each plant consists of a single 



