150 PRACTICAL BOTANY. 



not stained by this dye, but the cell contents take a pinkish 

 tinge. 



Prepare another mount of the yeast, burst some of the 

 cells, and run iodine solution under the cover glass. The 

 cell wall is rendered more distinct, the protoplasm is 

 slightly colored, but none of the particles are stained 

 blue. Starch is therefore not present, consequently 

 chlorophyl is absent. These reactions are all more dis- 

 tinct, if, instead of using a fresh preparation, a thin layer 

 of the yeast is allowed to dry on the cover glass. A drop 

 of water is then placed on it, the cover glass is put in 

 position on a glass slip, and the iodine is applied. 



Make another dry preparation on a cover glass, treat 

 with 70 per cent sulphuric acid for a few minutes, wash 

 out the acid with water, stain with dilute iodine solution, 

 and mount. The cell wall will be beautifully distinct in 

 some of the cells because of the shrinking of the proto- 

 plasm. 



The cell contents may also be made to shrink by mount- 

 ing some fresh yeast and running a drop of a ten per cent 

 solution of common salt in water under the cover glass. 

 The shrinking of the cell contents is due to the fact that 

 the solution used passes freely through the cell wall itself, 

 but does not pass through the thin layer of the protoplasm 

 that lines the cell. This treatment is called plasmolyzing 

 the cell. 



5. Prepare a dry layer of yeast on a slide and stain it 

 with Schultze's solution. This treatment stains the cell 

 walls of higher plants blue or violet, but gives a yellowish- 

 brown color to the cell walls of the Fungi. The material 

 of the cell wall is in this case fungous cellulose. That 

 fungous cellulose is closely related to ordinary cellulose is 

 proved by the fact that, after it has been treated with 

 dilute caustic potash for a long time, it gives the usual 

 blue or violet reaction with Schultze's solution. 



