Medullary ray facts for kids
In botany, medullary rays (pith rays or wood rays) are sheets or ribbons extending vertically through the tree perpendicular to the growth rings. The cells in each ray are elongate and horizontal. These are living cells, unlike the dead cells of the wood xylem.
The rays allow the radial transmission of sap. If wood is cut into boards with the growth rings roughly perpendicular to the face of the board, the medullary rays often produce beautiful "figure" such as silver grain, medullary spots, pith flecks, etc.
Medullary ray Facts for Kids. Kiddle Encyclopedia.