EXERCISE 21 



THE CHLOROPLASTS 

 i 



Materials. Thin leaves of a water plant, such as Elodea or Pota- 

 mogeton, or leaves of a moss (these should have been exposed to 

 direct sunlight for some hours before the study is made) ; compound 

 microscopes. 



Directions for work. Mount a piece of a leaf, or pieces of 

 several leaves, on a slide for examination with the microscope. 

 Observe the cells of the leaf with low power and high power. 



Where does the chlorophyll occur in the cells ? Describe the 

 cells and the chlorophyll bearers (chloroplasts). 



To determine the location of starch in the leaf cells, remove 

 the water from the slide by touching a piece of blotting paper 

 or filter paper to the edge of the cover slip. Add dilute iodine 

 at the other edge of the cover. Examine the leaves for evidences 

 of starch and note its relation to the chloroplasts. 



NOTE. From the textbook it may be learned that starch is present in 

 the leaves, as shown by the experiment, because it is manufactured there. 

 Sugar is present for the same reason, and more commonly than starch, but 

 there is no equally convenient test for its presence. The following exercises 

 will take up some of the conditions necessary for the making of such foods. 



References 



BERGEN and CALDWELL. Practical Botany, pp. 14, 15. 

 BERGEN and CALDWELL. Introduction to Botany, p. 37. 



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