What is Xylem Tissue?

To define Xylem, it is a transport tissue found in vascular plants along with phloem. The important function of xylem is to transport nutrients and water to leaves and stems from roots and also to provide support. The Xylem word was introduced by Carl Nageli in 1858. Now let us see the xylem diagram so that we can have a basic idea of xylem structure.

Xylem Diagram

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Types of Xylem 

Xylem is mainly of two types primary and secondary. They both perform the same function but they are categorized depending on the type of growth.

  • Primary Xylem: 

It will be formed with the primary growth of the plant. This growth can be found in the tips of the stems, roots and flower buds. This will make the plants grow taller and roots to grow longer. This is known as primary growth because it occurs first in the growing season. 

  • Secondary Xylem: 

This will be formed with the plant’s secondary growth and this will allow the plant to grow wider by the time. For example, wide tree trunks which show a lot of secondary growth. It will occur every year after primary growth. Secondary xylem is responsible for tree trunks dark rings which are used to determine the age of the tree. The two main groups of Plantae in which secondary xylem can be found are conifers and angiosperms.

What are the Components of Xylem?

Xylem is composed of mainly four types of cell in which some of them are living and some of them are dead.

  • Tracheids: 

These are the fundamental cells of the xylem, they are elongated with a tube-like structure having tapering in the end. A major portion of the tracheid's cell wall is perforated with pits. There are different patterns of secondary thickening in tracheids like annular thickening, Spiral thickening( helical thickening), scalariform thickening( ladder-like thickening), Pitted thickening and Reticulate thickening.

  • Vessels: 

These are also called as the trachea and they are the second category of xylem elements which is composed of short and tube-like cells. Components of the vessels are Vessel segments or vessel elements.

  • Xylem Fibres: 

Dead cells with lignified walls and a central lumen. Xylem fibres help in the transportation of water and provide mechanical support.

  • Xylem Parenchyma: 

They are only living cells and it stores starch and fat. They also help in transportation water for short distances. We can see all the components in the xylem diagram.

Xylem Structure and Function

Xylem Structure:

Xylem is composed of different types of cells. One of them is tracheids having long cells helps to transport xylem sap and provide structural support. Another is the vessel element which is smaller compared to the tracheids but even this helps in water conduction. Vessel elements form one continuous vessel with perforated plates which connects all vessel elements. It also contains xylem parenchyma, this tissue helps to make the softest part of the plant and long fibres which support the plant. When xylem is watched under a microscope, it appears like star-shaped. For the structure of xylem, the solution is almost the same. You can find more relevant information under the section named ‘what are the components of xylem?’.

Xylem Function

The most important function of xylem is to transport water and nutrients including minerals and inorganic nutrients from the roots of the plant to the other parts of the plant. The materials which flow through the xylem cell are called xylem sap. Substances are transported by passive transport, so it does not require any external energy. The phenomenon which allows the xylem sap to flow upward against gravity is called capillary action caused by the surface tension of the liquid.

The plant absorbs carbon dioxide from the atmosphere and water from the soil. Let's consider, when stomata in leaves open to absorb carbon dioxide, a lot of water get evaporated from the leaves. So, xylem is necessary to transport water at the site of photosynthesis and other parts of the plants.

Xylem Development

Proto xylem is the first xylem which develops in the growing plants and its vessels are narrow as the plant is not grown yet.  Metaxylem is developed in the late stage where it has larger vessels and cells. Protoxylem and metaxylem can be arranged in the four ways depending on the centrach, exarch, endarch and mesarch.

FAQs (Frequently Asked Questions)

1. Where is the Xylem?

Answer. Xylem can be found in the non-woody plants and the parts of the non-woody plants. It is also found in the secondary xylem formed by the meristem called vascular cambium in woody plants.

2. Why are Xylem Cells Dead?

Answer. Xylem is made up of two types of cell tracheids and vessel elements. Both of the cells are dead when they are used in the xylem. Dead cells, which don’t have organelle, help to transport more capacity of water.