Wood ray

The wood of Quercus robur, end grain, showing one large ray and several smaller rays

Oak, side grain, conspicuous rays

Maple, ray fleck, of rays smaller than in oak

A wood ray occurs in wood, and consists of bodies of cells running from the inside of the tree or shrub to the outside. That is, rays run at right angles to other cells of the xylem and phloem, which mostly run vertically. Rays serve to transport and store nutrients and chemical substances.

Rays may be low, that is only very few cells high, to very high, easily visible to the naked eye. Rays may be narrow, only one cell wide, to quite wide, many cells wide. A wood well-known for its high and wide rays is oak; less noticeable is that oak also has small rays. There are other woods with two types of rays.

Wood rays are sometimes called "medullary rays" or "pith rays" but this is only accurate for some of them, only when they run from the pith to the outside of the tree or shrub. Many rays do not start in the pith, but are formed later; as the circumference of the tree or shrub grows, more rays are necessary.

In wood products the rays can be seen running perpendicular to the growth rings. If wood is cut into boards with the growth rings roughly perpendicular to the face of the board, the rays can produce beautiful "figure", called ray flecks.

Bark

A ray does not stop at the edge of the wood, but continues on, into the bark. It is then called a bark ray.