Kim Collins, of Sarasota, Fla., for her question:

WHAT CAUSES KNOTS TO FORM IN WOOD?

    A slice of wood is marked with fine lines arranged in graceful patterns. This so called wood grain tells the story of how and when the living tree did its growing. In certain cone bearing trees, the streaky grain is mixed with dark gobs of harder wood. These tough knots tell something special about how the conifer trees grow.

    Knotty pine wood comes from sturdy evergreens, designed to keep their dark green boughs through the worst of the winter. This calls for special built in protections to seal out the frost, to withstand blustering gales and to shed extra burdens of snow that might break their heavy boughs.

    For this reason, the piny cone bearers build supplies of weatherproofing materials, such as waxes and gummy resins. The waxes are used to coat the surfaces of their leafy needles. The resins are built into the cells and cell walls and distributed throughout the woody tissues.