Vascular Tissue: Plant Logistics Management
Have you ever wondered how plants manufacture food and send it across to the various parts of the plant? The secret lies in the efficient transportation system made up of vascular tissue.
Vascular tissue in plants are a major, continuous and unified system – right from the root tip to every single leaf. Its presence is vital to the plant as it performs the function of conduction of matter from one end of the plant to the other end and vice-versa.
The vascular tissue, unlike the simple tissues (such as the parenchyma, sclerenchyma and collenchyma), are complex tissues made up of vascular bundles. These vascular bundles are made up of different kinds of cells are hence heterogeneous in composition. The complex tissues in plants comprise of the xylem and the phloem.
The xylem and phloem, based on their function, occupy specific positions in the plant. To begin with, the xylem is concerned with the absorption of water and minerals from the soil. Hence, it carries water and minerals from the root to the leaves via the intermediate plant organs. The phloem, on the other hand, conducts prepared food material throughout the plant. So in essence, the phloem carries processed food from the food factories (leaves) to the various other parts of the plant, down to the roots. Thus, the xylem and phloem are a two-way transporting system for the materials of sustenance of the plant.
The xylem and phloem are structurally also very complex. While most other tissues are a collection of a single type of cells (parenchyma), the xylem and phloem each are very complex. The xylem is made up of four different types of cells, namely the tracheids, vessels, xylem fibers and xylem parenchyma. Like the xylem, the phloem too is composed of different kinds of cells. They are the sieve tubes, sieve cells, companion cells, phloem fibers and phloem parenchyma.
Vascular bundles in action
Vascular bundles make up the complex circulatory system of the plant. However, based on the way they are positioned and function, the vascular bundles are classified into two groups: Conjoint and Radial Bundles. The characteristic features of these tissues can be observed by studying the cross-section of a plant part.
a) Conjoint Bundles
Conjoint bundles are present in the leaves and stems of plants. In this case, the xylem and phloem are placed side by side along a linear plane and run parallel to each other. Conjoint bundles are of three kinds:
- Collateral : xylem ring inside and phloem ring outside the xylem,
- Bicollateral: where a ring each of phloem is present both inner to and outside the xylem ring) and…
- Concentric : where one vascular tissue encircles the other
b) Radial Bundles
According to the structure of radial bundles, the xylem and phloem occur at different radii along the plant and are not in a circular or ring-like fashion.
Significance of Xylem and Phloem
Much importance has been given to the vascular tissue in plants, as they are the prime tissue for conduction of material. They are akin to the circulatory system in animals. The xylem consists of strong, fibrous tissue that adds to the support of the plant. Weak xylem pose a threat to its strength and rigidity. Similarly, the phloem serve to provide all plant organs with the necessary food. By the process of photosynthesis in the leaves, the phloem carries the prepared food around. When the phloem does not function well, the plant growth is stunted and wood quality becomes inferior. This affects the economic and trade value of wood that man utilizes for domestic and industrial purposes. As water and minerals are needed for the full development of the plant, it becomes inevitable that these tissues are formed completely and function efficiently.
Economically, the vascular tissue of plants serve a dual purpose. They are needed for the welfare of the plant as a whole. In addition, without proper wood, our homes would be unsteady and unsafe. The quality of the food consumed too would be inferior. The vascular tissue in plants are therefore responsible for a balanced interaction between the animal and plant kingdom at large.