Paul Dickey, age 12, of Cypress Inn,

How does wood grow?

Wood is made mostly from cellulose, the tough material from which cotton is made, A tree grows its wood, cell by cell, and these sturdy little boxlike calls era fitted tightly together and usually sealed for good measure with plant cement called lignin  The woody calls also may contain smidgins of sugar aria other minerals, and some of them contain liquid sap  The wood from almost avert' tries has its own grain and character which come from the way in which the woody cells are made and put together 

When you watch a tree growing, you see that its trunk gets wider and taller with every year, You naturally wonder how and where all this new woody growth i s' added  It i s added at the tips of the twigs and the branches and on the outer rim of the trunk, dust under the bark  If you have a magnifying glass, or better still a hand lens, you can discover where this wondrous work takes place, However, you need a powerful microscope to reveal the special cells which actually perform this magic 

If you pinch off a woody twig, you see that it is covered with a layer of soft, dark cells somewhat like cork, Gently peel them away and you may find a tender skin of greenish cells and then perhaps a layer of colorless cells which carry the liquid sap to feed the various outer skins of the twig, Thicker lagers of these same skins form the bark around the trunk of the tree  Together they form what is called the phloem of the trunk and twig 

When you peel off the bark, you some to the outer layer of woody tissue  A lens will show the sturdy little cell‑boxes to be about one  seventh of an inch wide, all neatly stacked together, wall to wall  The outer layer of wood is soft and springy with liquid sap running up and down the tree trunk 

This is called the sapwood  The inner layers get harder and drier towards the canter of the trunk, Here the cells are old and dead, and often darkened with deposits of resin and minerals 

This picture of a woody trunk does not tell us how or where new cells are added to the tree and neither will the magnifying glass However, you now know enough to guess where the new wood is formed The dry heartwood in the center of the trunk was obviously made first and the newest wood is the living sapwood around the edges 

The rest of the story must be gathered from careful studies made with the help of powerful microscopes Between the phloem and the wood there is a layer of miraculous cells called the cambium This colorless layer may be several cells or merely one call thick  In summer and especially spring when food is plentiful, the cambium cells divide and divide The new cells on the outer side form new layers of bark The new cells formed on the inner side add new layers of woody tissue to the tree trunk