74 PRACTICAL BOTANY. 



as the plant is very delicate. Place a mass of the 

 Vaucheria in water and agitate the water until some of 

 the plant filaments separate from the mass, free from 

 adhering dirt. Transfer some of these filaments to a 

 slide with a camel's hair brush. To prevent crushing the 

 plant support the cover glass with pieces of very thin 

 cover glass, or even with bits of paper. Notice that each 

 plant is made up of a single branched cell. Look for 

 colorless rhizoids, which may be found if the specimen 

 grew on the surface of soil. Draw a typical filament. 



3. Observe the green chromatophores scattered uni- 

 formly throughout the cell. Treat with iodine solution. 

 Is starch present ? Iodine solution turns starch blue or 

 blue black. Treat a quantity of Vaucheria with alcohol 

 for some minutes. Note the color of the alcohol. What 

 is the effect on the color of the Vaucheria ? To a little 

 of the alcoholic solution of chlorophyl in a test tube add 

 an equal volume of benzol and shake. The benzol, which 

 separates and rises to the top, extracts a blue-green color, 

 leaving the alcohol colored yellow green. The starch is 

 formed in the chlorophyl bodies and is dependent upon 

 the healthy condition of the chlorophyl. 



4. Place some Vaucheria in ordinary water and another 

 portion in water that has been boiled to drive out the 

 carbon dioxide. Set both in the sunlight for some hours. 

 Observe whether bubbles of gas rise in equal abundance 

 from both. The gas is oxygen. Chlorophyl-bearing plants 

 decompose carbon dioxide, assimilate the carbon, and set 

 oxygen free. Test some of the Vaucheria from each 

 vessel for starch. Is carbon dioxide necessary for the 

 production of starch ? Let both vessels stand two or 

 three days. Is carbon dioxide necessary for the healthy 

 growth of the plant ? 



5. Place some Vaucheria in each of two vessels of ordi- 

 nary water. Expose one to direct sunlight and exclude 



