EXERCISE 22 

 IS LIGHT NECESSARY FOR STARCH-MAKING IN LEAVES? 



Materials. Two potted plants, or two small plants (as clover) 

 growing -out of doors ; water bath ; beaker ; alcohol ; iodine. 



Directions for work. Put one plant in a dark closet at least 

 twenty-four hours before the experiment is to be performed, at 

 the same time placing the other in a window where it is ex- 

 posed to the rays of the sun for at least several hours pre- 

 ceding the experiment; or if potted plants are not available, 

 select two clover, plants in a meadow and cover one of them 

 with a bucket. 



Gather several leaves from each plant, remove the chlorophyll, 

 and test for starch as in Exercise 20. 



What differences, if any, do you find between the leaves 

 which have been in the dark and those which have been ex- 

 posed to the light ? What does this indicate about the necessity 

 of light for starch-making in leaves (photosynthesis) ? 



References 



BERGEN and CALDWELL. Practical Botany, pp. 15-17. 

 BERGEN and CALDWELL. Introduction to Botany, pp. 38, 39. 



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