Complex Permanent Tissue | Science for ACT PDF Download

Complex Permanent Tissue

•  The complex tissues are made of more than one type of cells and these work as a unit. Complex tissue are heterogenous.
• Complex tissues are absent in gametophytes.
•  During vascularization in plants differentiation of procambium followed by the formation of primary phloem and primary xylem simultaneously.

Complex tissues are of two types:
(a) Xylem
(b) Phloem

(a) Xylem

•  The term 'Xylem' is coined by Nageli.

• The function of xylem is to conduct water & minerals salts upwards from the roots to stem & leaves and to give mechanical strength to the plant body. 

• For conduction of water death of protoplasm is must. Dead tissues are more develop in water scares condition.

•  On the basis of origin, xylem is divided into primary xylem and secondary xylem.

1. Primary xylem originates from procambium during vascularization.
On the basis of development primary xylem divided into two parts
(1) Protoxylem
(2) Metaxylem  

•  Cells of protoxylem are small as compare to metaxylem

2. Secondary xylem originates from vascular cambium during secondary growth.

• The elements of xylem are

1. Tracheids 

•  Tracheids are primitive conducting elements of xylem.

•  A single tracheid is a highly elongated cell with hard, thick and lignified wall and a narrow lumen. The ends of tracheids are tapering or chisel like.

•  The tracheids found one above, the other are separated by cross wall which bear bordered pits.

•  Tracheids are dead and lignified cells. The deposition of lignin on cell wall is responsible to form a different type of thickenings.i.e., annular (primitive type), spiral, scalariform, reticulate and pitted.

Note : 

1. Usually bordered pits are present at the end wall of tracheids.

2. Maximum deposition of lignin is found in pitted type of thickening and pits are formed in this type of thickening.

3. Annular and Spiral type of thickening of lignin is found in protoxylem.

4. Reticulate and Pitted (mainly) type of thickening of lignin is found in metaxylem.

5. Scalariform type of thickening  is found in metaxylem tracheids of pteridophytes and  in metaxylem tracheids of Cycas.

6. End wall of tracheids are imperforated/pitted.

7. Tracheids are unicellular.

Note: Pits are unlignified areas on lignified wall

(2) Vessels

•  It is an advance conducting element of xylem. Vessels is a long cylindrical, tube like structure with lignified walls and, a wide central lumen.

•  The end wall is perforated (Transverse septum is absent between two vessel elements. If present then porous.) Thus vessels are more capable for conduction of water than tracheids. Due to presence of perforated end wall, vessels work as a pipe line during conduction of water.

•  The perforation may be simple (only one pore) or multiple (several pores). Vessels contain usually simple pits on their lateral walls. Types of thickening on the walls of vessels is the same as tracheids.

Note :

1. Vessels are found in most of the angiosperm but also present in some gymnosperms like Ephedra, Gnetum and Welwitschia.

2. Vessels are absent in some Angiospermic plants such as Dracaena, Yucca, Dagenaria,  Drimys.
There are some angiosperm families in which vessel less angiosperms are included. 

E.g.: Winteraceae, tetracentraceae and trochodendraceae.

3. Vessels are example of dead syncyte.

4. Vessels are multicellular.

3. Xylem Fibres

•  Xylem fibres provides strength to the tracheids and vessels. Mainly these fibres provide strength to the vessels.

•  They may be either septate or aseptate. They have obliterated central lumen.

• They are abundantly found in secondary xylem.

4. Xylem Parenchyma

•  It's cell wall is made up of cellulose.

Function : Radial conduction of water and  store food material in the form of starch or fats and tannin etc.

 Their walls possess pits.

Hadrom : – Tracheids and Vessels are collectively known as water conducting elements or "Hadrom". Hadrom term was proposed by Haberlandt.

(b) Phloem

• The term 'Phloem' is coined by Nageli.

•  The main function of the phloem is to conduct of food materials, usually from the leaf to other plant parts (eg. storage organ and growing regions) On the basis of origin, phloem is classified into two categories primary and secondary phloem.

• Primary phloem originates from procambium during vascularisation and secondary phloem originates from vascular cambium during secondary growth.

On the basis of development primary phloem categorised into protophloem and metaphloem.

•  The protophloem has narrow sieve tubes  whereas metaphloem has bigger sieve tubes.

•  Phloem remains active for less duration as compared to xylem.

Phloem consist of 4 types of cells:

1. Sieve Cell /Sieve Tube 

•  Sieve element was discovered by Hartig.

•  Sieve cells/sieve tube element are living and thin walled.

•  Mature sieve tube elements are enucleated living cells.

•  Central vacuole is present in each sieve cells/sieve tube element and around the central vacuole thin layer of cytoplasm is present.

•  In Angiosperm plants, sieve tube elements are joined their ends and  form sieve tube. Their end walls are perforated (Sieve Pores) in a sieve like manner to form the sieve plate. Translocation of food material takes place through these pores.

• Sieve elements contain special type of protein-P-protein (p-phloem). Most likely function of p-protein is sealing mechanism on wounding and it is also related with conduction of food.

Note :

1. Food conduction is bidirectional in sieve tube.

2. In sieve tube, oblique transverse perforated septa (sieve plates) are present at their end wall.

3. Sieve tube is an example of living syncyte.

2. Companion Cells

These are thin walled living cells. The sieve tube elements and companion cells are connected by pit fields present in their longitudinal walls, which is common wall for both and, with the death of one, other cell also dies.

•  A companion cell is laterally associated with each sieve tube element in Angiospermic plants.(In carrot more than one)

•  Sieve tube element and companion cell originates together. Both of them originates from a single mother cell. So called as sister cells.

•  The companion cells and sieve tube elements maintain close cytoplasmic connections with each other through plasmodesmata.

•  Companion cell is a living cell with large nucleus. This nucleus also controls the activity of cytoplasm of sieve tube element.

•  Companion cells are only found in Angiosperms. (exception - Austrobaileya is angiosperm plant but companion cells are absent).

• Special type of cells are attached with the sieve cells in gymnosperm (mainly) and in pteridophytes in place of companion cells. These cells are called as albuminous cells/ strasburger cell.

Note :

(1) Albuminous cells in conifers are analogous to companion cells of angiosperms. They are modified phloem parenchyma cells.

(2) The companion cells play an important role in the maintenance of a pressure gradient in the sieve tubes.

(3) In phloem of pteridophytes and gymnosperms sieve cell are present which are comparable to the tracheids.

3. Phloem Fibres / Bast Fibres

These are made up of sclerenchymatous cells.

•  These fibres are generally not found in primary phloem.

•  These fibres provide mechanical support to sieve elements (sieve cells and sieve tube).

4. Phloem Parenchyma

•  It's cells are living and thin walled. It store various materials. eg. Resin, Latex, Mucilage etc.

•  The main function of phloem parenchyma is conduction of food in radial direction and storage of food. The conducting element of pholem is called Leptom.

•  Leptom term was proposed by Haberlandt.

Note :

(1) Phloem parenchyma is absent in the stems of monocotyledon plants.  

(2) Phloem Parenchyma is absent in the stems of Ranunculaceae plants (dicot family).e.g. Thallictrum

Old NCERT Syllabus

SPECIAL TISSUE OR SECRETORY TISSUE

I. Lactiferous tissue : 

• These are made up of long, highly branched and thin walled cells. These cells are filled with milky juice, called as Latex.

•  Latex is the mixture of saccharides, starch granules, alkaloids, minerals and waste materials.

•  Starch granules present in latex are dumble shaped.

Function :

(1) Latex provide protection to the plant.

(2) It prevents the plants from infection of bacteria and fungus. In laticiferous tissue there are two types of cells.

1.  Latex vessels and 2. Latex cells

1. Latex vessels :

•  These are articulated.

•  These are syncytic cells and coenocytic (multinucleated).

Example :- Latex vessels are present in Hevea, Ficus, Papaver, papaya, Argemone and Sonchus.

•  Opium is obtained from the latex of Papaver somniferum. It contains an alkaloid named as morphine.

•  An enzyme papain is obtained from the latex of papaya (Carica  papaya).

•  Para rubber/Commercial rubber is obtained from Hevea bransiliensis and Indian rubber is obtained from Ficus elastica Mostly latex is white in colour but in some plants latex is coloured.

Ex. Papaver – Dark brown

Argemone            
Yellow colour
Sonchus

In some plants latex is colourless Ex. Banana (Family - musaceae).

2. Latex cells :

These are non articulated. These are long, branched and multinucleated cells (coenocytic cells).
Example - Latex cells are found in Calotropis, Euphorbia and Nerium (Apocyanaceae), Ficus religiosa Note : Latex vessels and latex cells are found in cortex.

II. Glandular tissue : 

• As the name indicates that this tissue is made up of glands. These glands contain secretory or excretory materials.

•  Glandular tissues have two types of glands :-

(1) Unicellular. Ex. - Urtica-dioica. These cells are present on the surface of the leaves. These are spiny glands.

(2) Multicellular : Multicellular glands are of two types.

1. External Glands :- These are located on the surface of the plants and arising as an outgrowth from the epidermis. These glands are of various types :-

   Glandular hairs :- They secrete gum - like sticky substances in tobacco and Plumbago.

    Nectar Glands :- These glands secrete sugar solution. These are found in floral parts mainly in thalamus.

These glands secrete nectar to attracting the insects.

Exception- In Passiflora, nectar glands are found in leaves.

2. Internal Glands :- These glands are embedded in the tissues. Internal glands are of following types.

 Digestive glands :- Digestive glands are found in insectivorous plants. These glands compensate the deficiency of N2 in insectivorous plants. These are found in Utricularia, Drosera, Dionaea etc. plants. they secrete proteolytic juice.

Mucous glands :- These glands secretes mucous. These are found in the leaves of betel.

Oil glands :- These secretes Volatile oil. It act as antiseptic. These glands are found in fruits & leaves of lemon & orange. Mostly, Oil glands are lysigenous but in sunflower these glands are schizogenous.

Note : Oil glands which secrete volatile oils called osmophores. Osmophores develop fragrance in flowers. Oils which are obtained from Eucalyptus leaves are used in medicines.

(d) Tannin, resin, gum secretory glands are also internal glands.These are schizogenous. Maximum resin glands are found in Pinus. Resin ducts are schizogenous. Gum glands are found in Acacia.

(e) Water glands/Hydathode.

These glands are related with guttation. Hydathodes are present in Tomato, Pistia and

Eichhornia etc.