Plant Tissues

Introduction

This article will talk about important topics about plant tissues, as students can expect direct questions from this chapter. What are plant tissues, you ask? Well, a tissue is a group of cells having similar or dissimilar cells, having a common origin and performing specific functions.

Classification Of Tissues

The plant tissues are mainly classified into the following categories:

• Meristematic tissues or meristems
• Permanent tissues
• Secretory tissues

Now, let us discuss each of the plant tissues in detail.

Meristematic Tissues And Its Types

Meristematic tissues can be characterised as follows:

• They contain young cells
• They are capable of continual divisions and are metabolically very active
• Meristematic tissues lack vacuoles
• An abundance of cytoplasm is found in them
• Meristematic tissues have no intercellular space
• They have a thin homogeneous wall

They are classified based on origin, location or function

1. Based on origin:

•  Promeristem: it is found in the places where a part of the plant body is initiated
• Primary Meristem: located in the apices of roots, leaf primordial, it originates from promeristem and retains its functions
• Secondary Meristem: it arises in permanent tissues

2. Based on functions:

• Protoderm: it is the external layer of the apical meristem
• Ground meristem: it comprises the major part of the apical meristem and forms the ground tissues like the endodermis, cortex
• Procambium: occurring inside the protoderm, the young cells of the tissue give rise to the primary vascular system

3. Based on location:

• Intercalary Meristem: the portion of the apical meristem that is separated from the apex during the growth of permanent tissues is the intercalary meristem
•  Apical Meristem: it is located at the growing apices of lateral roots; these cells observe the linear growth of the organ
• Lateral Meristem: these cells are responsible for increasing the diameter of an organ

4. Based on cell division:

• Plate Meristem: under this, the cell division occurs through two planes resulting in a flat plate of tissue
• File Meristem: when the cells divide anti clinically in one plane, it is file or rib meristem
• Mass Meristem: when the cells divide anti clinically in all planes resulting in the formation of mast cells, it is mass meristem

Permanent Tissues And Its Types

Unlike meristematic tissues, permanent tissues are made up of mature cells which cannot further divide themselves and have a permanent shape, function and size. The cells are either thin or thick-walled and can be dead or living. Permanent tissues are of two types:

1. Simple permanent tissues include parenchyma, collenchyma and sclerenchyma.
2. Complex permanent tissues have two categories, i.e., xylem and phloem.

They are further explained as under:

1. Simple Permanent Tissues: Groups of cells that are similar in terms of form, function and origin are simple tissues. They are further classified as:

• Parenchyma: mainly concerned with vegetative activities of the plant; it is the simplest tissue
• Collenchyma: Made up of cellulose, hemicellulose and pectin, the cells in it are thickened around the corners and contain protoplasm. It is the tissue of the primary body. The term collenchyma was proposed by Schleiden
• Sclerenchyma: The cells of this tissue vary in size and shape and consist of thick-walled dead cells

2. Complex Permanent Tissues: Complex tissues are classified into two categories:

• Xylem: It is made up of tracheids, xylem parenchyma, vessels and xylem fibres, out of which two vessels and tracheids are the main transporting material. It also consists of two primary xylems, namely protoxylem and metaxylem
• Phloem: It is composed of sieve tube elements, companion cells, phloem parenchyma, phloem fibres, and phloem fibres in angiosperms. Whereas in gymnosperms, albuminous and sieve cells are present instead of sieve tubes and companion cells

 Special Permanent Tissues

Also called secretory tissues, these types of plant tissues are structurally modified to carry out functions secretory. It is classified into the following two categories:

• Laticiferous Tissue: the cells of the tissue are filled with milky juice called latex. The tissue is composed of long, branched and thin-walled cells
• Glandular Tissue: this type of tissue consists of secretory or excretory materials. They possess various glands that secrete oil, tannin, and mucilage

Conclusion

It can be concluded that plant tissues have three categories, namely Meristematic tissues or meristems, permanent tissues and secretory tissues. Meristematic tissues can be further divided based on origin, function, location and cell division.