What are tracheids?

Hint: Elongated cells of xylem with broad lumen and tapering ends are known as tracheids. The shape of the cells is polygonal with thickening due to depositions. Tracheids have a lignified secondary wall. Bordered or simple pits are also present.

Complete answer: Xylem is a type of vascular tissue responsible for the transportation of water and nutrients from the roots to various parts of plants. Major components of xylem are xylem parenchyma, xylem fibres, tracheids and xylem vessels. Tracheids are cells of xylem that function in the transportation of water and minerals in the plant. Two forms of tracheary elements are tracheids and vessel elements. At maturity, the protoplast is lost in tracheids and they become non-living. Two cell walls are present namely, primary and secondary wall. The secondary cell wall is lignified and is present between the plasma membrane and primary wall, several thickening patterns are present such as annular, spiral, scalariform, reticulate and pitted. Concave depressions are present on the cell wall known as pits. Cells present close to each other have complementary pits through which water is moved across the cells. In pteridophytes, only tracheids perform the function of water conduction and gymnosperm wood is mainly composed of tracheids.

Note: Tracheids are 5-6 cm in length with lignified cell walls. These are non-living cells as the protoplasm is lost at maturity. Different types of thickening patterns are present in between primary and secondary walls of tracheids. The role of tracheids in the conduction of water and minerals.