Q.Write short notes on Tyloses.

Tyloses are bubble-like protoplasmic outgrowths of xylem parenchyma cells that push through pits into adjacent old, non-conducting xylem vessels, plugging them and contributing to the hardness, dark colour, and decay-resistance of heartwood.

As a woody stem ages, its central, older xylem (the part farthest from the cambium) gradually stops conducting water and becomes converted into heartwood — a darker, harder, non-functional core, distinct from the lighter, water-conducting outer sapwood.

One of the changes that accompanies this conversion is the formation of tyloses:

• Living xylem parenchyma cells that lie adjacent to a vessel push balloon-like outgrowths of their protoplast through the pits in the vessel wall, ballooning INTO the lumen (cavity) of the vessel.
• These tylosis outgrowths can enlarge until they completely occlude (block) the vessel's cavity.
• Tyloses often become impregnated with tannins, resins, gums, and other substances, which give heartwood its characteristic darker colour and contribute to its resistance to fungal/microbial decay and insect attack, making heartwood more durable than sapwood. …