1. Simple tissues
Simple tissues are homogeneous and include cells with same structure and function. There are three main kinds: Parenchyma, collenchyma and sclerenchyma (Figure 1).
Figure 1: Parenchyma, collenchyma and sclerenchyma.
(i) Parenchyma: The most common tissue is parenchyma, which is morphologically and physiologically simple and unspecialized. These cells may be found in the epidermis, cortex, pericycle, pith, and other tissues. They are in charge of photosynthesis, food storage, secretion, and so forth.
(iii) Sclerenchyma: Long, thick-walled, lignified cells with tapering ends. These look like fibres and are also known as sclerenchymatous fibres. These are dead cells that provide a mechanical purpose.
2. Complex tissues
The complex tissues are made up of several kinds of cells that execute various activities. These are classified into two types: xylem and phloem (Figure 2).
Figure 2: Xylem and Phloem
Xylem is made up of both living and non-living cells. Tracheids, vessels, xylem fibres, and xylem parenchyma are the four components of xylem.
Tracheids: Tracheids are dead cells with elongated or tube-like walls that are rigid, thick, and lignified. Their tips are tapered, blunt, or chiselled. Their role is to conduct water and provide mechanical assistance to the facility.
Vessels: The vessel is a long cylindrical tube-like structure with lignified walls and a broad central lumen. The cells are lifeless because they lack protoplast. The cells are placed in a longitudinal series with perforated partitioned walls (transverse walls), giving the overall structure the appearance of a water pipe. Their primary purpose is the transportation of water and minerals. Mechanical strength is also provided.
Xylem fibers: These cells are elongated, lignified, and have points on both ends. A xylem fibre aids in the transport of water and nutrients from the root to the leaf while also providing mechanical support to the plant.
Xylem Parenchyma: The cells are living and thin walled. The main function of xylem parenchyma is to store starch and fatty substances.
Phloem consists of four types of elements sieve tubes, companion cells, and phloem parenchyma and phloem fibers
Sieve tube: These are thin, tube-like cells arranged end to end. The perforated transverse walls at the ends are known as sieve plates. The primary purpose of sieve tubes is to transport food from the plant’s leaves to its storage organs.
Companion Cells: These are elongated cells attached to the lateral wall of the sieve tubes. These are mostly found in angiosperms.
Phloem Parenchyma: The phloem parenchymas are living cells which have cytoplasm and nucleus. Their function is to store food materials.
Phloem fibers: Phloem fibres are the common name for sclerenchymatous cells found in the main and secondary phloem. These cells are elongated, lignified, and give the plant body with mechanical strength.
3. Special tissues
Special tissues are structurally modified and specially organized for secretary function. These are of two types: Laticiferous tissues and Glandular tissue (Figure 3).
Laticiferous tissues: These are specialized tube like structures known as laticiferous ducts found in many angiosperms. These ducts are filled with white or yellow latex. Laticiferous ducts are of two types: Latex cells as found in madar and Latex vessels as found in rubber, papaya etc.
Glandular tissue: It consists of different types of glands which are formed by single cell or group of cells. These secrete resin, oil, mucilage, tannin, gums etc.