THE ALG^E. 85 



is collected in masses scattered through the cells the 

 chlorophyl bodies or chromatophores. Draw a single cell 

 and a group of cells, showing the minute structure. 



3. Run a little iodine solution under the cover glass ; 

 the cell contents take a yellowish-brown color, showing 

 that protoplasm is present. A nucleus containing a 

 nucleolus can be seen in each cell unless the iodine solu- 

 tion is too strong and gives too intense a coloration. 

 The cell wall is unaffected by the iodine. Draw and 

 compare with drawing under Number 2. 



4. Run sulphuric acid into the preparation that was 

 stained with iodine in Number 3. The cell wall turns 

 blue or violet. It is, therefore, composed of cellulose 

 such as is found in ordinary plants. Treat a fresh mount 

 with Schultze's solution, which should give the same 

 result. 



5. Place pieces of bark bearing Protococcus in a glass 

 of water and expose to the sunlight for several days. 

 Observe that bubbles of gas rise from the water. It is 

 oxygen. Protococcus growing in pools t)f stagnant water 

 under favorable conditions gives off oxygen so freely that 

 a dense, frothy scum forms on the surface of the water. 

 If some Protococcus from such a pool be placed in a test 

 tube inverted over mercury, the oxygen gas may be col- 

 lected in such quantity that it may be tested by a spark. 



6. Examine scrapings from the bark used in Number 5, 

 or Protococcus from a stagnant pool, under high power. 

 The mount will be found to be swarming with rapidly 

 moving organisms. These are the zoospores, or motile 

 forms of Protococcus. Large forms, megazoospores, and 

 small ones, microzoospores, will be present. It is hard to 

 persuade one's self that they are not animals. (Fig. 43, 

 B.) The motion is produced by the rapid lashing of the 

 water by two flagella, which extend from the anterior end 

 of the body of the organism. These can be seen under 



