EXERCISE 20 

 PRODUCTION OF STARCH IN LEAVES 



Materials. Fresh leaves, both green and variegated green and 

 white (such as geranium), which have been exposed to the sun for 

 several hours ; alcohol ; iodine solution ; glass or metal beaker or 

 cup ; water bath. 



Directions for work. 1. Dip each of the leaves in boiling 

 water for a few seconds in order to kill the leaf tissues. Trans- 

 fer them to alcohol in a beaker and keep the alcohol warm over 

 a water bath for about ten minutes. When the leaves are 

 removed they should be without green color. Where has the 

 green coloring material (chlorophyll) gone ? 



2. Place a number of the leaves in a weak solution of iodine 

 (tincture of iodine) and allow them to remain in the solution 

 about ten minutes or until decided changes of color are seen. 

 Note the location of the colored parts, particularly in the 

 variegated leaves. 



3. Put a small quantity of starch in a test tube, add a few 

 drops of iodine solution, and shake the tube. Note the result- 

 ing color. Boil the water for a few minutes, cool, and add 

 iodine. Note color. 



4. What substance did the test reveal in the leaves ? Did 

 its location in the variegated leaves have any relation to the 

 location of the chlorophyll, and if so, what ? 



References 



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

 BERGEN and CALDWELL. Introduction to Botany, pp. 37-40. 



[23] 



