198 COLLEGE BOTANY 



and oils, proteins and other compounds (page 139). The proc- 

 esses by which these and other compo'unds are formed is not 

 clearly understood, but they involve other elements, such as 

 nitrogen, sulfur, phosphorus, etc. (see page 201). The fats are 

 composed of the same elements as are found in the carbohydrates, 

 but the amount of oxygen is proportionately less. There are 

 many kinds of proteins, but they all contain carbon, hydrogen, 

 oxygen and nitrogen, and frequently sulfur and phosphorus. It 

 is very generally believed that they are formed in the leaves, 

 but sunlight does not appear to be a necessary factor. 



LABORATORY EXERCISES. 



Exercise 1. Select a plant with stomata on one side (Goleus or Phase- 

 olus muUiflorus) and keep in dark for 12 to 24 hours. Cover half of upper 

 surface of one leaf and half of lower surface of another With vaseline. 

 Expose to sunlight as long as possible. Remove as much of the vaseline 

 as possible by wiping and place the leaves in warm 95 per cent, alcohol 

 for 24 hours. When well blea<;hed place them in a, solution of iodine in 

 potassium iodide. Examine for starch. Explain. 



Exercise 2. Chlorophyll. Make an extract of chlorophyll by dipping 

 leaves in hot water and then soaking in warm alcohol. Put in test tubes 

 and examine under both reflected and transmitted light. 



Exercise 3. Reduce the alcoholic extract to 80 per cent. Put 20 e.e. in 

 a test tube and add 20 c.c. of benzole. Shake thoroughly and allow to settle. 

 Note the color produced by the two pigments. 



Exercise If. Take two potted plants of the same kind. Keep one in the 

 dark for 12 to 24 hours and expose the other to light during the day. 

 Between 1 and 3 o'clock p.m. test the leaves of both for starch as in Exer- 

 cise No. 1. 



Exercise 5. Put some Poiamogelon sp. or Elodea sp. under a funnel 

 in a beaker of water. Put a test tube full of water over the tip of the 

 funnel. Set in the bright sunlight and note the rise of gas in the tube. 



Exercise 6. Remove an actively growing leaf from a plant early in the 

 morning and another in the afternoon of a bright day. Place in boiling 

 water for one minute and then in alcohol for a few hours to remove chloro- 

 phyll. Then in a, solution of iodine. A blue color indicates starch. Which 

 contains the most starch? Cut sections of both and examine. 



Exercise 7. Soak red leaves of Coleus in a 5 per cent, aqueous solu- 

 tion of ether to remove the red coloring matter. Examine for chlorophyll. 



Exercise 8. Grow seedlings in darkness. Expose one lot to light. 

 Note the appearance of the green and compare the future growth of the two. 



Exercise 9. Cover a growing plant and a glass of potassium hydroxide 

 solution with a bell jar. The solution removes the COa from the air. 

 After a few days, test leaves for starch. Compare with a plant grown 

 under a bell jar without potassium hydroxide. 



