60 THE BIOLOGY OF THE CELL 



results. Does starch form more or less rapidly in 

 this case than in II. a. ? 

 What conclusions do you draw from these two ex- 

 periments ? 



B. — Growth. 



a. Put some filaments of Sjpirogyra into a bottle 

 containing distilled water, and set the bottle in 

 the sunlight. 

 5. Put some filaments of Spirogyra into a bottle 

 containing Sachs's food-solution for green plants. 

 Let the two bottles stand in the sunlight for a 

 week or two, then compare the results found in 

 each experiment. In which bottle do the plants 

 grow better ? Explain. 



C. — Cell-formation. 



a. Place some actively growing filaments of Spiro- 

 gyra in a cold place (almost freezing) overnight. 

 Examine them early next day for cells in the 

 process of division. What are the first steps in 

 the process? What changes take place in the 

 nucleus ? In the chromatophores ? In the cell- 

 wall? Is the process confined to any particular 

 part of the filament ? To particular cells ? How 

 long does it last ? Can you now account for the 

 difference in thickness between the end and side 

 walls ? Would you consider ceU-formation to be 

 a kind of reproduction ? Why ? In what re- 

 spects is cell-formation in the plant different from 

 spore-formation ? 

 Make drawings showing the various stages of ceU- 

 formation seen. 



Oeneral Questions. — Is a filament of Sjpirogyra a sin- 



