THE ALG^E. 75 



the light entirely from the other, having all other condi- 

 tions the same. After two or three days determine 

 whether the sunlight is necessary for the healthy develop- 

 ment of the plant. 



6. In a fresh mount of Vaucheria look for bright shin- 

 ing oil globules scattered among the chromatophores. 

 Treat with a one per cent solution of osmic acid. This 

 demonstrates the presence of oil globules by turning them 

 black. 



7. Run under the cover of a fresh mount ten per cent 

 salt solution and study the primordial utricle or layer of 

 protoplasm which lines the cell. The salt solution finds 

 easy entrance through the cellulose cell wall, but does not 

 so easily find entrance to the cell contents. It also extracts 

 water from 'the cell contents, which consequently assume 

 a diminished volume. This treatment is called plasmolyz- 

 ing the cell. 



This experiment is also very instructive as illustrating 

 the manner in which the solutions that furnish nutriment 

 to plants which grow wholly immersed in water find en- 

 trance to the cells. As a further illustration, tie pieces of 

 bladder over the ends of a short piece of glass tube, of 

 a diameter of about half an inch, having filled the tube 

 with a saturated solution of sugar in water. Immerse in 

 water, and after a time the bladder diaphragms will be 

 bulged out because water has passed through them into 

 the sugar solution by endosmosis ; sugar also passes out by 

 exosmosis, as may be determined by tasting the water or 

 submitting it to chemical tests. 



8. Run dilute caustic potash under the cover of another 

 preparation and study the cell wall. Treat still another 

 mount with Schultze's solution ; this solution stains nor- 

 mal cellulose blue or violet. Is the cell wall composed of 

 normal cellulose? 



9. Keep some of the Vaucheria moist and in the dark 



