Monocot stem like Zea mays, vascular bundles are conjoint, collateral and closed. In vascular bundles, the lowermost protoxylem vessels and xylem parenchyma cells dissolve forming a water containing schizolysigenous cavity called protoxylem cavity or lacuna or lysigenous cavity. phloem parenchyma is absent.

Water-containing Cavities in Vascular Bundles of Monocot Stem

The water-containing cavities present within the vascular bundles of a monocot stem are known as vascular cavities. These cavities are also referred to as water-conducting vessels or water-conducting cells. They play a crucial role in the transportation of water and minerals throughout the plant.

Structure of Vascular Cavities:
The vascular cavities are composed of several types of specialized cells that work together to facilitate the movement of water. These cells include:

1. Vessel Elements: These are long, tube-like cells with perforated end walls called sieve plates. Vessel elements are stacked end to end, forming a continuous pipeline for water transport. They are dead cells, lacking protoplasts, and their primary function is to provide a conduit for water movement.

2. Tracheids: Tracheids are another type of water-conducting cells found in the vascular cavities. They are elongated cells with tapered ends and pits on their walls. Tracheids are alive at maturity and play a role in water transport, although they are less efficient compared to vessel elements.

3. Companion Cells: Companion cells are specialized parenchyma cells that are closely associated with sieve tube elements. They provide metabolic support to the sieve tubes by supplying them with necessary nutrients.

Function of Vascular Cavities:
The vascular cavities within the vascular bundles of monocot stems serve several important functions:

1. Water Transport: The primary function of vascular cavities is to transport water and dissolved minerals throughout the plant. Water moves through the vessel elements and tracheids via a process called capillary action. This movement is driven by transpiration, the evaporation of water from the leaves.

2. Support: The presence of vascular cavities provides structural support to the stem, allowing it to withstand mechanical stress and maintain an upright posture.

3. Nutrient Transport: In addition to water, vascular cavities also facilitate the transport of nutrients, such as sugars, hormones, and organic compounds, throughout the plant. This is achieved through the interconnected network of sieve tube elements and companion cells.

4. Storage: Vascular cavities can also store water and nutrients, acting as reservoirs during times of water scarcity or nutrient deficiency.

Conclusion:
The water-containing cavities, or vascular cavities, within the vascular bundles of monocot stems are vital for water and nutrient transport in plants. They consist of vessel elements, tracheids, and companion cells that work together to facilitate efficient movement and distribution of water and minerals throughout the plant. These cavities also provide support and act as storage sites, ensuring the overall health and survival of the plant.