EXERCISE 37 

 WHAT IS THE NATURE AND USE OF THE OUTER COVERING OF THE LEAF? 



Materials. Some rather thick leaves (life plant (Bryopliyllum) and live-forever are good, as 

 are most species of lily, iris, and amaryllis). 



Directions. Peel off a bit of the " skin " (epidermis) from each surface of the leaf, noting 

 especially its thinness and transparency. If you cannot peel off the epidermis, try to scrape away 

 one covering and all the other material of the leaf from a small area, leaving only the other 

 epidermis. Write notes describing the epidermis. 



Describe the kind of material that fills the space between the upper and the lower epidermis. It 

 is called the mesophyll, meaning " middle leaf." Is it easily injured ? Let a piece of the leaf, with 

 epidermis removed, lie on the desk for a while, and note the effect on the mesophyll. 



Explain the use of the epidermis with proofs secured from your study. See pages 71 74, 

 " Elements of General Science," for a discussion of the internal structure of the leaf. 



Additional problems. Examine a piece of the epidermis, mounted in water, under the microscope. Note the 

 shape of the cells. Are they all of one kind ? Can you locate the crescent-shaped cells (guard cells) with 

 the slit-like opening between them ? These, with the openings, are the so-called " breathing pores " or 

 stomata. Do the guard cells have chloroplasts ? Are the guard cells of the same shape in all stomata ? 

 in stomata of different leaves ? at different times of day ? 



Study a cross section of a leaf. 



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