Plant Histology
Introduction
A tissue is an aggregation of cells that have a common origin and structure, and perform similar functions. Tissues are meant for meeting the physical and physiological needs of the plant body.
Meristematic Tissue (Meristem)
The meristematic tissue is formed exclusively by undifferentiated or embryonic cells. These cells, known as meristematic cells, are responsible for bringing about growth of the plant body due to their capacity to undergo continuous mitotic divisions.
Permanent Tissues (Mature Tissues)
The permanent tissues are formed by the differentiated cells, which become specialised to perform specific functions like protection, support, storage and conduction. The permanent tissues always differentiate from the meristematic cells, during the process of growth.
Simple Permanent Tissues
These tissues are described as homogenous, since the constituent cells are identical in their structure.
Parenchyma
It is the main tissue in the plant body, occurring in almost all regions. It is particularly abundant in the root and stem. It is the least specialised among the permanent tissues. The cells of the tissues are called parenchyma cells. These cells are usually spherical or oval in shape. Sometimes the cells may be elongated. Very rarely, the cells become irregular in shape. They are usually loosely arranged with prominent intercellular spaces. In certain regions like epidermis, the cells become compactly arranged and hence, intercellular spaces are absent.
Collenchyma
It is a type of simple permanent tissue, which is mainly meant for providing mechanical support to the shoot system of a plant. Collenchyma is completely absent in the root.
Sclerenchyma
It is a type of simple permanent tissue mainly meant for providing mechanical support and protection to different parts of the plant body. Hence, sclerenchyma occurs in all the parts of the plant body, including the fruit and seed.
Xylem
It is a complex permanent tissue, which is specialized for the conduction of water and mineral substances in the plant body. Xylem is a heterogenous tissue made up of four different types of cellular elements.
Phloem
Phloem is a complex permanent tissue, which is specialized for the conduction of food and other organic substances. Phloem is also a heterogenous tissue.
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