ADAPTATIONS OF A LEAF 
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surfaces), palisade layer under top epidermis; spongy layer , body of 
leaf; vein. Which cells contain chlorophyll ? 
HOME WORK ON LEAVES 
Pull up or cut off a large burdock plant. Measure the area covered 
by the lower leaves. What else grew in this area? What is its condi¬ 
tion? Why? Do the same with plantain, dock, dandelion, knotweed, 
and other weeds in dooryard or garden. What plants form rosettes of 
leaves in the fall? 
Break off leaves of burdock, plantain, dock, and pieplant. Note 
the strings (fibrovascular bundles). 
Make a collection of leaves to illustrate the various kinds of shape, 
apex, margin, and base. 
Study the arrangement of leaves on the plants you see to determine 
how it is adapted to secure light for all the leaves. 
What effect does the wind have in helping or hindering leaves to 
get light? 
What happens when you make a “bag” from a leaf of live-for-ever? 
How can you tell guttation drops from dew? 
252. Adaptations of a Leaf. — The cutin of the epidermis 
prevents evaporation of water. The stomata allow air to 
enter and water and gases to pass out. Stomata themselves 
show many adaptations : (1) Position. In a leaf that extends 
horizontally from a plant, most of the stomata are on the 
under side, an adaptation which prevents their being closed 
by water. In leaves which float upon the water, the stomata 
are on the upper surface for the same reason. In plants with 
erect leaves, the stomata are distributed on both sides. 
In the cases of desert plants, the stomata are sunk below 
the level of the epidermis, or they are covered by hairs or 
wax, both of which tend to keep them from being filled with 
water and to prevent undue transpiration (evaporation). 
(2) The structure. This shows other adaptations. The 
opening is surrounded by two cells, called guard cells-, which 
have the property of absorbing water from the atmosphere. 
When these cells are full of moisture, they are plump or 
turgid; when they have only a little water they are flabby 
