EXERCISE 35 



IS THERE A FOOD MATERIAL IN THE LEAF, AND DOES IT HAVE ANY RELATION 



TO CHLOROPHYLL? 



Materials. A fresh white .potato or some commercial starch ; plants with white-spotted or par- 

 tially green leaves, as some kinds of geraniums ; dilute solution of iodine (tincture of iodine) ; the 

 apparatus and materials used in the preceding exercise. 



Directions. Cut a thin slice from the potato or spread out some commercial starch on a glass 

 plate, and place upon it a drop of the dilute iodine solution. What is the color of starch when 

 treated with this solution ? 



Select a number of leaves which have been exposed to the sun for several hours. Remove them 

 from the plant. Note carefully and make sketches to show the size and location of the light spots 

 of the leaf. Remove the chlorophyll from the leaves as in the preceding experiment. 



When the chlorophyll has been removed from the leaves, take them from the alcohol, place them 

 in a dish, and cover them with some of the dilute iodine solution. 



In five or ten minutes examine the leaves. What do the results show ? Examine the variegated 

 leaves to determine whether there is any relation between the location of the starch and the location 

 of the chlorophyll. 



Additional problems. Can non-chlorophyll-bearing plants make food material ? 

 Do plant stems contain chlorophyll ? 

 Where is the chlorophyll in a cactus plant ? 



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