Question

Write short notes on tracheids.

Answer 1

Hint: Xylem tracheids are said to be elongated with tapering ends as well as broad lumen. The secondary wall of these cells is lignified. They appear as polygonal along with thick-walled. Pits are simple or bordered. The cell wall thickenings are because of the deposition of secondary wall substances.

Complete answer:
As said before Tracheids are considered to be elongated cells in the xylem of vascular plants that serve in the transportation of water as well as mineral salts. Tracheids are one of two forms of treachery elements, vessel elements being the other. Tracheids, unlike vessel elements, do not have perforation plates in them.
All tracheary elements developed a thick lignified cell wall, along with it at maturity the protoplast has broken down as well as disappeared. The presence of tracheary elements is the general defining characteristic of vascular plants to differentiate them from non-vascular plants. The two key functions that tracheids may fulfill are contributing to the transportation system along with it provide structural support.
The secondary walls in tracheary have thickenings in various types such as annular rings; as continuous helices also known as helical or spiral; as a network also called reticulate; as transverse nets known as scalariform and, as extensive thickenings except in the region of pits known as called pitted.

Note: Tracheids gives most of the structural support in softwoods, where they are the key cell form. Due to tracheids having a much higher surface to volume ratio compared to vessel elements, they further serve to hold water against gravity by adhesion when its transpiration is not occurring. This is likely to be one of the mechanisms that helps plants prevent air embolisms.