FOR WAGGONER’S BIOLOGY 
27 
EXERCISE 29 
THE EXTERNAL STRUCTURE OF A LEAF 
I. Preliminary Laboratory Study. Examine a simple leaf, 
identifying the following structures: stipules (if present), petiole, 
blade, veins. Define each. (Refer to the text, if necessary. See 
Waggoner, Fig. 78.) Note the thickness of the leaf as compared 
with its length and breadth. Note the color. What is the rela¬ 
tion of the petiole to the veins and the branching of the veins? 
Draw the leaf. 
II. Field Study. Examine each of the following (or similar 
types), observing the position on the branch, the bud in the axil 
(the angle between the stem and the petiole of the leaf), and the 
form of each leaf: the apple or peach, the rose, walnut, hickory, 
box elder or ash, and the horse-chestnut. Determine which leaves 
are simple and which are compound. 
III. Laboratory Study. Use for this purpose the leaf of a 
geranium, live-for-ever, or Wandering Jew. Peel ofi’ the under 
surface layer — the epidermis — of the leaf. Examine with a lens. 
Study when mounted under the low and the high power of the 
compound microscope. Note the walls of the epidermal cells. 
Note the oval objects. These are stomates. Of how many cells 
is a stomate composed? These are guard cells. What is their 
position with reference to one another? Note the openings between 
them. What purpose is served by the stomates? Why is the wash¬ 
ing of leaves by rain or artificial means of value to the plant? Is 
there chlorophyll in the epidermis? In the guard cells? What is 
the function of chlorophyll? Draw some of this epidermis, showing 
epidermal cells and stomates. 
IV. What is a leaf? Why is it an expanded structure? Why 
does it need air and sunlight? What would happen to a plant if it 
were kept stripped of its leaves? Why? 
