pit

noun

The stony endocarp of a drupe, as in a peach or cherry. The small openings in the walls of tracheids and vessel elements which allow water to move from cell to cell. The equivalent structures in primary cell walls are called primary pit fields, areas where plasmodesmata are concentrated and pit development usually occurs. A pit comprises a pit membrane, consisting of the middle lamella plus the primary wall; and a pit cavity, the depression in the secondary wall. Pits usually occur in pairs (called pit pairs) on either side of the middle lamella between two adjacent cells.