WATER SILK 55 



magenta, which are substances which stain 

 protoplasm especially. "What is the effect on 

 the chromatophores ? On the cell- wall ? Of 

 what substance are the chromatophores com- 

 posed ? 



3. The pyrenoids and starch, grains (seen in the 



chromatophores). — Apply picric acid to make 

 the pyrenoids more plainly visible. How are 

 the pyrenoids arranged ? "What is their color ? 

 Shape ? Kun a drop of iodine under the cover- 

 glass and note the position and number of the 

 starch grains. "What is their relation to the 

 pyrenoid ? Do they at all affect the shape of 

 the chromatophore ? Examine some of the 

 cells treated with alcohol in the second experi- 

 ment. Does carmine or magenta stain the 

 pyrenoid ? Of what substance is the pyrenoid 

 composed ? Treat with iodine some other cells 

 which have been in alcohol. Is starch still 

 present in these cells ? Explain. Do you find 

 starch grains anywhere else than in the neigh- 

 borhood of the pyrenoid ? 



4. The nucleus. — "What is its position in the cell? 



Shape? Color? Canyon find the nucleolus? If 

 so, what is its position ? Shape ? In which cells 

 is the nucleus seen most distinctly ? Notice the 

 strands of protoplasm radiating from the nu- 

 cleus. To what do they run ? How many can 

 you find ? Examine the nucleus in cells treated 

 with alcohol, iodine, magenta, etc. 



5. The primordial utricle or protoplasmic sac. 



— Try to see this (without using reagents) as a 

 thin film of protoplasm lining the cell-wall. If 

 unsuccessful, plasmolyze the cell by running a 



