X..] PROTOCOCCUS. 393 



Size; (measure) — very variable. 

 Form; more or less spheroidal, with individual 

 variations. 



Structure; cell-wall, protoplasm, chromatophores, some- 

 times a vacuole, always a nucleus containing a 

 nucleolus. 



Colour; generally green — sometimes red — sometimes 

 half and half — sometimes centre red, periphery 

 green — the colouring matter always in the proto- 

 plasm of the chromatophores only. 



Draw carefully to scale. 



2. Apply the methods of mechanical and chemical 

 analysis detailed for Torula. (I. A. 3. 4. 5. 6.) The 

 application of iodine . is especially useful for bringing 

 out the limits of the chromatophores, and also the 

 nucleus and nucleolus. The same reagent will also 

 often show the presence of some small starch-grains. 

 Treat a specimen with strong iodine solution and 

 then with sulphuric acid (75 per cent.): the cell-wall 

 will become stained blue. 



3. Look out for cells the contents of which are dividing 

 up to form zoospores. 



b. Zoospores. 



a. Mount a drop of water containing zoospores of 

 Protococcus, and examine with a high power. 

 Note the actively locomotive green bodies, of 

 which two varieties can be distinguished. 

 a. Cells of relatively large size derived from 

 the vegetative cells by division of their con- 

 tents into 2 or 4 portions. These are the 

 macrozoospores. Observe the thin colour- 



