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PLANT TISSUE

PLANT TISSUE The first embryonic plant tissue develops as a result of mitotic division of the zygote after fertilisation.

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PLANT TISSUE ARE CATEGORISED INTO TWO GROUPS: 1.MERISTEMATIC TISSUE 2.PERMANENT TISSUE

1.MERISTEMATIC TISSUE MERISTEMATIC TISSUES ARE CATEGORISED IN TWO DIFFERENT WAYS: 1.ACCORDING TO THEIR LOCATION AS Apical Intercalary Lateral 2.ACCORDING TO THEIR ORIGIN AS Primary Secondary

1.According to location a.Apical Meristematic Tissue: Apical meristematic tissue is located at the tip of the root,stem and braches. It provides longitudinal growth of these organs.

b.Intercalary Meristematic Tissue: Intercalary Meristematic Tissue is located between permanent tissue at the point where a leaf or side branch develops.For example at the base of internode. It also provides longitudinal growth.

c.Lateral Meristematic Tissue: It is located laterally within the stem or root and provides an increase in the diameter or girth of a plant.

2.According to Origin a.Primary Meristematic Tissue: It retains the ability to divide through out the life of the plant. It is located at the tips of roots,stem and branches. The region where the cell continously divides is known as the growth region.

b.Secondary Meristematic Tissue: It is composed of permanent tissue cells that have regained their ability to divide by the stimulation of hormones. Cambium and spongy cambium are examples of this type of meristematic tissue.

CAMBIUM:A plant tissue consisting of actively dividing cells that is responsible for increasing the girth of the plant, it causes secondary growth. Click

2. PERMANENT TISSUE Permanent tissues are divided into the following groups according to their structure : Parenchymatous Dermal Supportive Vascular Glandular

1.Parenchymatous Tissue Parenchymatous cells form the bulk of the tissues of the root, stem cortex and leaf mesophyll layer. They are large, thin walled and generally undifferentiated. Functions: healing, regeneration of damaged structures, photosynthesis, respiration, storage, secretion and movement of water and food.

2.Dermal Tissue Dermal tissue covers the outer surface of the root stem, leaves and fruits, protecting the inner cells from external hazards. It consists of epidermis and periderm. It functions in the reduction of water loss in terrestrial plants during hot and dry periods.

3. Supportive Tissue All higher land plants require support to help them withstand the effects of environmental conditions such as wind and rain. Woody plants require a stronger system of support and have extensive supportive tissues known as collenchyma and sclerenchyma.

a. Collenchymas: is a living tissue found in the leaves and stalks of flowers and fruits of actively growing perennial plant it is also found in some annual plants. Collenchymas cells usually form strands or rings giving flexibility as well as mechanical support.

b. Sclerenchyma: is the main supporting tissue of woody plants. As each cell matures, it accumulates first cellulose and pectin, then becomes lignified. Sclerenchyma cells may be in the form of individual round cells known as stone cells and are found in fruits such as pears and quince.

4. Vascular Tissue All terrestrial plants need a vascular system to transport minerals and water to the leaves for photosynthesis, and then to distribute the products of photosynthesis through the plant. Their vascular tissue is composed of xylem and phloem vessels.

XYLEM: transport water and water soluble elements from root to the leaves. PHLOEM: transports the products of photosynthesis from the leaves to the other areas of the plant.

Vascular Bundles: The vascular bundles form the main transport system of higher plants and consist of xylem and phloem vessels. In dicotyledons that have no secondary growth, the vascular bundles are initially arranged in a circle around the outside of the pith. The xylem and phloem vessels are separated by a layer of meristematic tissue known as cambium. In monocotyledons, the xylem and phloem are irregularly arranged in bundles through out the ground tissue of the stem and there is no cambium between them.

5.Secretory Tissue Secretory cells may function either as a group or individually. Their by-products of metabolism perform many useful roles. Resins and tanins are secretions that protect the plant from attack by pathogens. Nectar provides an energy source for insects which in turn pollinate the female gametophyte. Alkaloids are secretory poisons that defend the plant against herbivores.

a.External Secretory Tissues 1. Hydathodes 2. Nectaries 3. Digestive Glands

b. Internal Secretory Tissues 1.Lactiferous tissues 2.Multicellular Glands: Schizogenous Glands Lysigenous Glands Schizolysigenous Glands