Water conduction in the stem of a tree takes place primarily through the sapwood. The sapwood, also known as the xylem, is the layer of wood in a tree that is actively involved in water transport. It is responsible for carrying water and dissolved minerals from the roots to the leaves of the tree.

The process of water conduction in the sapwood can be explained in the following steps:

1. Water uptake: The roots of the tree absorb water from the soil through root hairs. This water moves into the root cells and then enters the xylem vessels located in the sapwood.

2. Cohesion-tension theory: Water moves upwards in the sapwood due to a phenomenon called the cohesion-tension theory. According to this theory, water molecules in the xylem are held together by cohesive forces, creating a continuous water column.

3. Transpiration: The movement of water through the sapwood is driven by transpiration, which is the loss of water vapor from the leaves. As water evaporates from the stomata (tiny openings on the leaf surface), it creates a negative pressure or tension in the xylem, pulling water upwards.

4. Capillary action: Capillary action also aids in water conduction. The narrow xylem vessels in the sapwood have a small diameter, which allows water to rise against gravity. This capillary action helps in the movement of water upwards.

5. Adhesion: Adhesion, the attraction between water molecules and the xylem walls, also contributes to water conduction. Water adheres to the walls of the xylem vessels, counteracting gravity and facilitating upward movement.

6. Root pressure: In some plants, root pressure can also play a role in water conduction. Root pressure is the force exerted by the roots to push water upwards. This pressure can help in moving water through the sapwood, especially during times of high soil moisture or low transpiration.

While the sapwood is the primary site of water conduction in the stem of a tree, it is important to note that other tissues such as the duramen (heartwood) and the primary xylem also contribute to water transport to some extent. However, the sapwood is the most active and efficient tissue for water conduction.