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What are simple tissues? Describe salient features and functions of meristematic tissue ?

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These tissues are composed of similar type of cells which have common origin and function. They are further grouped under three categories parenchyma, collenchyma and sclcrenchyma.

(i) Parenchyma:
Parenchyma (Greek, para = beside; en – chein = to pour) is most simple and unspecialized tissue which is concmed mainly with the ordinary vegetative activities of the plant. It is phylogenetically and ontogenctically the primitive tissue. The tissue mainly consists of thin walled living cells which have intercellular spaces between them The cell wall is made of cellulose or calcium pectate. Possesses a prominent nucleus and vacuolate cytoplasm.

The intercellular spaces are either formed schizogenously (i.e by splitting apart of the middle lamellae region between cells) or lysigenously. However, they remain attached by plasmodesmata. Sometimes the intercellular spaces are absent.b Each individual parenchymatous cell may be spherical, oval, cylindrical, rectangular, stellate or long spindle like. It is that cells varies in different plants and in different organs of the same plant.

Parenchyma is distributed in almost all the parts of plant body constitutiong the vegetative ground tissue. It is found in epidermis, cortex, pith, pericycle, mesophyll of leaves, pulp of fruits, endosperm of seeds and in meristematic tissues. Parenchymatous cells are also found in xylem and phloem.

Functions of Parenchyma: Parenchymatous tissue performs the following functions in different plant organs –

  1. Storage of reserve food materials.
  2. Storage of water in succulents, (e.g., Opuntia, Euphorbia)
  3. Buoyancy and gaseous exchange in water plants. (Aerenchyma).
  4. Provide rigidity to plant body due to turgidity and help to maintain the shape of plant body.
  5. They give rise to secondary meristem in the form of cork cambium and vasular cambium, (secondary growth and healing)
  6. They perform all vital activities of plants.
  7. Sometimes develop chloroplasts and called as chlorenchyma and take part in photosynthesis.


 

(ii) Collenchyma:
Collenchyma (Greek, colla = glue; enchyma an infusion) is the tissue of primary body. The cells of this tissue contain protoplasm and are living. The cell walls show localized thickenings due to presence of approximately 45% pectin, 35 % hemicellulose and 20 % cellulose. They are never lignified but may possess simple pits. Presence of cellulose and pectic substances in the cell wall accounts for the high water absorbing capacity to the cells. The tissue is plastic, extensible and has capacity to expand and gives a tensile strenth to the organ.

Originates from elongated cells that resemble procambium. Thus, the cells are generally elongated with oblique end walls. Sometimes the ends may be rounded. They occure chiefly in the hvpodermis of dicotyledonous stems (e.g. cucurbita, helianthus) and leaves. They are usually absent in monocots and in roots. However, they may occur in root cortex if the root is exposed to light.

Functions of Collenchyma:

  1. It is the chief supporting tissue in young dicotyledonous stems.
  2. Has capacity to expand and gives a tensile strength to the body.
  3. It is present at the margins of some leaves and resists tearing effect of the wind.
  4. Some cells possess chloroplasts and perform photosynthesis.

Sclereids:
The sclerenchvmatous cells, which are short and possess extremely thick lamellated lignified waIls with long tubular simple pits are called sciereids. They originate from ordinary parenchymatous cells by the deposition of secondary wall layers. The’ mas’ be simple or branched.  The sciereids vary greatly in their shape and size. they may be spherical, oval, cylindrical, T shaped, dumbell – shaped or even stellate. They are usually shorter than fibers.

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