Light micrograph (radial longitudinal section) of the wood of a primitive conifer, Auracaria cunninghamia, the monkey puzzle tree. The micrograph shows pits (yellow & blue spots) within the tracheids (cylinder cells). Tracheids are relatively primitive, non-living cells of the xylem. They are elongated with tapering ends & have thick lignified walls. They provide mechanical support & conduct water for the plant. Pits are cavities in the tracheids, which allow exchange of substances between adjacent cells. The thinner cross walls here are medullary rays. For a fossil ancestor of this conifer see E440/037. Magnification X40 at 35mm size.