44 THE BIOLOGY OF THE CELL 



on the cover -glass, and examine. Note the 

 shape, color, and structure of the fibres. 



2. Run a drop of strong iodine under the cover- 



glass. What is the effect upon the fibres ? 

 Compare vrith the same treatment of the cell- 

 wall of green slime. 



3. Follow the iodine with a drop of seventy-five per 



cent, sulphuric acid. What change ? Compare 

 with the preceding experiment and with the 

 color of the green slime after such treatment. 

 The preceding and this experiment together con- 

 stitute the iodine-sulphuric acid test for cellulose. 

 How does it differ from the test for starch ? 



4. Mount some cotton fibres as in the first experi- 



ment, then run under the cover-glass a drop of 

 dilute chlor-iodide of zinc. What is the effect 

 upon the fibres ? Compare with that produced 

 by iodine and sulphuric acid used together, and 

 with the effect upon the wall of the cells of 

 green slime. Is the cell -wall of green slime 

 composed of cellulose ? 



B. Rejproductive Condition. 



In addition to the motionless or vegetative cells, 

 certain others, the zoospores, will probably be 

 found actively moving about. If they are not 

 found in the material when first gathered, they 

 are likely to appear if water containing the vege- 

 tative cells be left exposed to the sunlight for a 

 few days. The zoospores are of two sizes, the 

 larger being called macrozobspores and the 

 smaller microzobspores. Examine the shape, 

 size, and structure of each. Try to find vegeta- 

 tive cells whose contents are dividing into 2-4 



