Wood Cells and the Meaning of Grain

Though little more than water, a clump of cellulose, lignin and other chemicals, nature provides a structure and diversity that makes wood a classic and versatile building material. In its native state, or processed into forms that are unrecognizable, the wood fiber, or tracheid, is the basic building block of the stock with which we create chairs, cabinets, fine furniture or houses. These long, narrow cells arranged parallel to the length of the tree’s trunk are the grain of the wood, that characteristic which gives strength and flexibility to our medium. Grain indicates the plane of weakness of the wood but also shows us where it’s strength lies – aspects of lumber that we use to our advantage if we know how they work.

Wood cells, or fibers as we shall call them, vary in size and shape, but are always quite long and pointed at the ends. They consist of a cell wall made of cellulose, with an open interior cavity and are glued together with lignin. The fact that they are long and run parallel to the long axis of the tree is what gives wood it’s grain. They are more easily pried apart than cut laterally which is why a deft blow with an axe can almost effortlessly split a log vertically but chopping from the side, a straight blow will do little more than knock off some bark.

The open space inside the fiber may or may not be filled with deposits of gum or resins, or tyloses. Tyloses are crystalline deposits found in the pores of some hardwoods, like white oak. They fill the pores completely making the wood water tight, which is why boat builders use white oak instead of red oak for planking.

Not all wood cells are oriented vertically. Rays are horizontally oriented groups of wood fibers that move sap and water radially across the grain. They are planes of weakness along which cracking can occur but can contribute overall to the beauty and figure of the finished piece.