66 THE BIOLOGY OF THE CELL 



drop of ten per cent, salt or sugar solution un- 

 der the cover-glass, and note how the proto- 

 plasm shrinks away from the ceU-wall. What 

 is the cause of the shrinkage of the protoplasm 

 when the cell is plasmolyzed ? What proper- 

 ties of protoplasm does the experiment illus- 

 trate ? What becomes of the chromatophores ? 

 What change takes place in the cell- wall ? Try 

 plasmolyzing the cell with a twenty per cent, 

 solution of salt or sugar. What difference in 

 the action of this and of the weaker solution ? 

 Plasmolyze with a two per cent, salt solution. 

 As soon as the protoplasmic sac shows plainly, 

 remove the salt solution and replace it with 

 water. Does the sac expand until it again fills 

 the entire cell? Explain. Explain all of the 

 changes noticed. 

 6. The vacuole. — Note that a large part of the ceU 

 is occupied by the vacuole. What change takes 

 place in this when the cell is plasmolyzed ? Ex- 

 plain. Examine several cells to note the varia- 

 tion in the size of the vacuole. Explain. 

 Draw a single filament seen from the side to show its 

 structure, ends, etc. ; a single cell seen sidewise to show 

 its contents, structure of wall, etc. ; the same cell seen 

 from the end with contents in natural position ; another 

 cell plasmolyzed. 



B. — Reproductive Condition. 



a. General appearance. — Can you, without using a mi- 

 croscope, distinguish this condition in any way, 

 as by difference in color of the mass, length of 

 filament, position in aquarium, etc., from the veg- 

 etative condition ? 



