Capillarity in plants:
Capillarity is the phenomenon by which liquids can rise or be drawn into narrow spaces against the force of gravity. In plants, capillarity plays a crucial role in the movement of water and nutrients from the roots to the upper parts of the plant.

Importance of capillarity in plants:
Capillarity helps in the transport of water and dissolved nutrients from the soil to the different parts of the plant. It is especially important in tall plants where the force of gravity alone is not sufficient to move water upwards against the resistance of gravity.

Factors aiding capillarity in plants:
Capillarity is aided by several factors in plants. One of these factors is the small diameter of the tracheary elements.

Tracheary elements:
Tracheary elements are specialized cells found in the xylem tissue of plants. They are responsible for the transport of water and minerals from the roots to the leaves. Tracheary elements include both tracheids and vessel elements.

Small diameter of tracheary elements:
The small diameter of tracheary elements aids capillarity in plants. This is because they have narrow and elongated cell walls with numerous pits. These pits allow for the movement of water and nutrients between adjacent cells.

Capillary action in tracheary elements:
Capillary action is the ability of a liquid to flow in narrow spaces without the assistance of external forces like gravity. In the case of tracheary elements, capillary action is facilitated by the small diameter and the narrow pits present in the cell walls.

Water movement in tracheary elements:
When water is absorbed by the roots, it moves upwards through the xylem vessels. The small diameter of the tracheary elements enables capillary action, allowing water to be drawn up against the force of gravity. This movement of water is essential for the transport of nutrients and the maintenance of turgidity in plant cells.

Conclusion:
The small diameter of the tracheary elements in plants aids capillarity by allowing for capillary action, which facilitates the movement of water and nutrients from the roots to the upper parts of the plant. This mechanism is crucial for the survival and growth of plants, especially tall ones.