22 PLANT BIOLOGY 



IV. MANUFACTURE OF THE FOOD SUBSTANCES BY PLANTS 



29. Is starch present in the green leaves of a plant that 

 has been exposed to sunlight? Laboratory Study No. 14. 



Take several leaves from a vigorous plant (e.g. geranium, 

 hydrangea) which has been exposed to bright sunlight for 

 a number of hours. Boil them a few moments in a large test 

 tube or flask of water ; pour off the water, add alcohol, and 

 boil carefully over a piece of wire gauze or asbestos until all 

 the green coloring matter has been removed. Rinse the leaves 

 in water, add iodine solution, and spread the leaves on saucers, 

 or in Petri dishes. 



1. Describe in your own words how the experiment was 



performed. 



2. Is starch present in the leaves ? How do you know ? 



3. Why was it necessary to remove the green coloring 



matter from the leaves before testing for starch? (If 

 you are in doubt, add some iodine to green leaves.) 



4. (Optional.) How may grass stains be removed from clothing ? 



30. Is starch present in the green leaves of a plant that 

 has been deprived of sunlight? 1 Laboratory Study No. 15. 



Put a vigorous plant (e.g. fuchsia, squash, sunflower, or 

 bean seedling) in darkness for 48 hours or more. Remove 

 several leaves, and treat them as described in 29 above. 



1. State briefly how the preparation of this experiment dif- 



fers from that in the previous experiment. 



2. Give your observation and conclusion. 



3. State, therefore, whether sunlight is or is not necessary 



for the manufacture of starch in green leaves. 



31. Is starch present in colorless portions of green leaves? 



Laboratory Study No. 16. 



1 A most suggestive series of experiments on the formation of 

 starch in green leaves is found in the Botanical Gazette for September, 

 1909, pp. 224-228, by Sophia Eckerson, of Smith College. 



