The given figures A (tracheid) and B (vessel) are types of xylem (C). Xylem is the vascular tissue in plants which conducts water and dissolved nutrients upwards from the root and also helps to form the woody element in the stem. It consists of tracheids, vessels, parenchyma cells, and woody fibres.
Tracheid is an elongated, tapering xylem cell having lignified, and pitted, intact walls which lacks perforations in the cell wall. Tracheids have pits where the cell wall is modified into a thin membrane, across which water flows from tracheid to tracheid. The cells die when mature, leaving only their lignified cell walls. Tracheids are found in all vascular plants. It is adapted for conduction and support.
Vessels are a long straight chain made of tough long dead cells known as vessel elements or vessel members. The vessel cells, devoid of protoplasm, are arranged end to end and the cell walls have disappeared. This makes a tube. They have a lignified cell wall and a large central cavity.
