Richard Ehler., Age 8. Of Ida Grove, Ia..For his question:

Why does wood have a grain?

A tree trunk is made from boxy cells, too small for our eyes to see. New cells are added around the outside of the trunk. In winter,, the cells are small and packed tightly together. They form a ring of hard, dark wood around the tree trunk. In a good growing season,, the new cells are large and they form a ring of softer., paler wood.

When we cut across the tree trunk, we see the rings of light and dark wood. When we cut a board of wood., the slice is taken up and down the tree trunk. The lines of light and dark wood run up and down. They give us the streaky marks we call the grain of the wood.