HOW SOME FAMILIAR THINGS LOOK 99 
portant part of the plant. Plants truly live on 
air and water and nothing else, a thing no other 
living creature can do. Their water supply runs 
through the woody fibers from the earth into 
the stem and then into the leaf cells, and the 
air comes in through the openings, or stomas. 
From these two substances the plant manu¬ 
factures its food. 
Sometimes we can see in the thin-walled 
cells, full of water and green grains and pro¬ 
toplasm, a little round body which is called the 
nucleus . This nucleus may be said to be the 
brain substance of the cell, in which its life 
functions center. If we want to make the 
nucleus easier to see, we can stain the cell with 
red or blue dye. The nucleus will absorb more 
color than the rest of the cell and thus stand 
out clearly. 
This is what the maple leaf looks like when 
we cut it through crossways. If we want to 
see what the skin looks like from above, we 
can lay a transparent young leaf flat under the 
microscope and look at it that way. When we 
What is 
the nucleus? 
