100 
WORLD OF INVISIBLE LIFE 
Why are the tops 
of leaves waxy? 
look at the under side, we find that the skin, 
too, is made up of little oblong, stretched-out 
cells with thin walls. The stomas look even 
more like human mouths. They are long nar¬ 
row openings with a cell on either side which 
looks like a lip. There are usually many fine 
hairs on this lower skin. Each hair is a single 
tube-like cell, or series of cells, connected to a 
flat cell in the skin. These hairs form the fuzzy 
surface we so often see on the backs of leaves. 
When we turn the leaf over and look at the 
top skin, we find that it has no hair and no 
stomas. It is composed of long flat cells which 
have a shiny surface of wax. The wax prevents 
the rain from staying on the leaf and protects it 
against the evaporation of water through the 
cell walls. 
We have to shave a thin slice from a pine 
wood chip in order to examine it under the mi¬ 
croscope. When we look at it we see that it, 
too, is made of long, narrow cells with rather 
thick walls. The cells extend up and down in 
the trunk of the tree, and they have pointed ends 
