HOW SOME FAMILIAR THINGS LOOK 97 
The stomas also regulate the water supply of 
the plant. If it is full of water, the lips of the 
opening will open and allow it to evaporate. In 
other words, the plant perspires. But if the 
plant is a little dry, the lips close up and no 
water is lost. The water which is necessary 
to plant life does not go in through these open¬ 
ings, however. Plants usually do not absorb 
water through their leaves, but only through 
their roots. It is taken in from the earth by the 
roots and rises through the woody fibers of the 
stem into the leaves. Then it passes out of the 
leaf into the air through the stomas. 
The upper skin has no openings. Between 
the upper and lower skins of the leaf are a 
great many irregularly shaped compartments 
called cells, with thin walls between them. 
They look somewhat like a honeycomb. They 
are crowded closely together just under the 
upper skin, but below are more spongy, with air 
spaces between them. Through this mass of 
thin-walled cells run little groups of thick- 
walled cells, which are the woody fibers of the 
What is the 
inside of a 
leaf like? 
