Tyloses: Definition, Structure and Functions

What are Tyloses? Tyloses (singular – tylosis) are the balloon like outgrowth of parenchymatous cells to the lumen of tracheids or vessels of the secondary xylem. The axial and ray parenchyma of the xylem develops protrusion and these protrusions enter or invade into the lumen of tracheids or vessels through pits. This invasion of parenchyma occurs when tracheids or vessels become inactive or damaged.

Who discovered Tyloses?

Malpighi (1686) for the first time reported the ‘balloon-shaped sacs’ in the lumen of vessels of heartwood and he named it as tyloses based on the Greek word ‘Thyllen’ meaning ‘bag’ or ‘container’.

How Tyloses are Formed?

Tyloses development occurs through the pit-pairs connecting parenchyma and tracheids or vessels. Sometimes many tyloses originate from a single parenchymatous cell. The tyloses completely fill the lumen of the vessel or tracheid and block the path. Tyloses are particularly rich in the tracheids and vessels of heartwood than sapwood.

The nucleus and protoplasm of parenchyma are retained in the tyloses. Usually tyloses stay as thin walled in the lumen of vessel or tracheids. Sometimes secondary thickening also occurs in tyloses. Very rarely, in some plants, the tyloses differentiate into sclereids with very thick lignified cell wall. Pruning or other stem injuries induce the tylosis formation in many horticultural plant varieties.

Tyloses accumulate resins and other secondary materials in their protoplasm. They are responsible for the characteristic odor of the wood. They also prevent the degradation of wood by termites and mites.

What are the Functions of Tyloses?

Ø  Prevent the leakage of water through damaged xylem

Ø  Prevent the invasion of pathogens through vessels or tracheids

Ø  Assist in the formation of heartwood

Ø  Tyloses formation is the main reason for Compartmentalization Of Decay In Trees (CODIT)

Ø  Tyloses store resins, gums and many ergastic substances

Ø  These ergastic substances give the wood a characteristic odour, helps in identification

Ø  Ergastic substances present in the tyloses can protect the wood from termites and mites

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