EXPERIMENT 2 Objective. To prepare temporary stained glycerine mount of transverse section of dicot stem/monocot stem/dicot root/monocot root.

                                EXPERIMENT 2

Objective. To prepare temporary stained glycerine mount of transverse section of dicot stem/monocot stem/dicot root/monocot root.

REQUIREMENTS

Fresh or preserved material of dicot (sunflower) stem/monocot (maize) stem/dicot (gram) root/monocot (maize)root, pith (Calotropis stem/carrot/radish), sharp razor or new blade, microscope, slides, coverslips, watch glass,petridish, saffranin/haemotoxylin, glycerine, brush, needle, blotting paper.

PROCEDURE

1.Take a 2-3 cm long piece of the material to be sectioned.

2.Fix the material properly in the pith.

3.Hold the pith containing the material to be sectioned horizontally between thumb and first finger of your left hand.

4.Hold the razor in the right hand with edge of the blade facing you and handle at right angle to it. 

5.Dip the top of the pith containing material and the razor in water.

6.Cut the sections of the material quickly and transfer the sections in water.

7.Select a thin uniform and com-plete section and place it in a drop of water on a glass slide.

8.Put 2-3 drops of stain over the section and allow it to stand for two minutes.

9.Wash away the excess stain with water.

10.Put a drop of glycerine over the section and cover it with the coverslip.

11.Observe the section under the microscope.

OBSERVATIONS

1. T.S. of Dicot Stem (Sunflower stem; See Fig. 2.2)

A TS. of dicot stem shows following structures:

1.Epidermis. It is an outermost layer made up of barrel shaped parenchyma cells. It is covered with cuticle towards outside and bears multicellular hair. 

2. Hypodermis. It lies below the epidermis and is made up of few layers of collenchyma cells.

3. Cortex. It is made up of several layers of parenchyma cells.

4. Endodermis. It is a single layer of barrel shaped parenchymatous cells that separates vascular tissues from cortex. It is also called starch sheath as its cells contain starch.

5. Pericycle. It is made up of few layers of sclerenchyma and parenchyma cells occurring in alternate patches.A patch of sclerenchyma cells lies above each vascular bundle.

6. Vascular bundles. The vascular bundles are wedge shaped and are arranged in a ring. Each vascular bundle is conjoint (ie., xylem and phloem occur in the same bundle), colleteral (.e., phloem lies toward the outerside and xylem occurs towards the inner side), and open (Le., cambium is present between phloem and xylem). Xylem in endarch (ie., metaxylem lies towards the outerside and protoxylem lies towards the inner side).

7. Medullary rays. They are made up of parenchyma cells between the vascular bundles.

8. Pith. It consists of parenchyma cells and lies in the centre of the stem.

Features of Identification

1. Presence of multicellular hair on the epidermis.

2. Presence of collenchymatous hypodermis.

3. Vascular bundles are wedge shaped and are arranged in a ring.

4. Each V.B. is conjoint, collateral and open.

5. Xylem endarch.

6. Pith is present in the centre.

2. T.S. of Monocot Stem (Maize stem; See Fig. 2.3)

A T.S. of monocot stem shows following structures:

1. Epidermis. It is an outermost layer made up of parenchyma cells. It possesses cuticle on its outer sum

2. Hypodermis. It consists of few layers of sclerenchyma cells.

3. Ground tissue. It is composed of parenchymatous tissue and extends from hypodermis to the centre. 

4. Vascular bundles. They are numerous and lie scattered in the ground tissue. Each vascular bund oval in shape and possesses a sclerenchymatous sheath. Each vascular bundle is conjoint (i.e., phloem xylem occur in the same vascular bundle), colleteral (i.e., phloem lies towards outerside and xylem occurs towards centre) and closed (ie., cambium is absent between phloem and xylem). Xylem is endarch (i.e.protoxylem lies towards the centre). Xylem vessels are arranged in V-shape manner A water-filled cavity called lysigenous cavity is present in each vascular bundle in protoxylem region. 

Features of Identification

1. Absence of short hair.

2. Hypodermis is sclerenchymatous.

3. Ground tissue is undifferentiated.

4. Vascular bundles are oval in shape, numerous and are scattered in the ground tissue.

5. Each vascular bundle is conjoint, colleteral and closed. It is surrounded by a bundle sheath. 

6. Xylem is V-shaped and endarch.

T.S. of Dicot Root (Gram Root, See Fig. 2.4)

ATS. of young dicot root shows the following structures

1. Epiblema or Piliferous layer. It is a single, outermost layer of thin walled, compactly arranged cells.Some cells of epiblema bear thin walled tubular outgrowths called root hair. 

2. Cortex. It lies below epiblema and is made up of many layers of thin walled parenchyma cells.

3. Endodermis. It is a single layer of barrel shaped cells. It separates the cortex from vascular tissues. The cells of endodermis possess band of thickening called casparian band.

4. Pericycle. It is a single layer of thin walled cells below the endodermis.

5. Vascular bundles. There are present 2-6 alternately arranged bundles of xylem and phloem called radial bundles. Xylem bundles are exarch i.e., protoxylem lies towards the outerside and metaxylem towards the centre. Xylem vessels are polygonal in outline.

6. Cojunctive tissue. Phloem and xylem bundles are separated from each other by parenchyma cells called conjunctive tissue.

7. Pith. It is absent or highly reduced in the form of few parenchyma cells.

Features of Identification

1. Presence of unicellular hair on the epidermis.

2. Vascular bundles are radial

3. Xylem/phloem bundles are less than 6.

4. Xylem exarch.

5. Pith is either reduced or absent.

4. T.S. of Monocot Root (Maize Root; See Fig. 2.5)

A T.S. of monocot root shows the following structures!

1. Epiblema or Piliferous layer. It is a single outermost layer of thin walled compactly arranged cells. Some cells of it give rise to unicellular root hair.

2. Cortex. It is quite wide and is made up of many layers of parenchyma cells.

3. Endodermis. It is the inner boundary of cortex and is made up of single layer of barrel shaped cells. The endodermal cells possess bands of thickening called casparian bands.

4. Pericycle. It is a single layer of parenchymatous cells and lies below the endodermis.

5. Vascular bundles. There are present many (8 or more) alternate bundles of xylem and phloem called radial bundles. Xylem bundles are exarch i.e.protoxylem lies towards the outerside and metaxylem towards the centre.Xylem vessels are rounded or oval in outline.

6. Conjunctive tissue. Phloem and xylem bundles are separated from each other by parenchyma tissue called conjunctive tissue.

7. Pith. The centre of the root is occupied by a well developed pith, made up of parenchyma cells.

Features of Identification

1. Presence of unicellular hair on the epidermis.

2. Vascular bundles are radial.

3. Xylem/phloem bundles are more than 6.

4. Xylem is exarch.

5. Large pith is present in the centre.

PRECAUTIONS

1. The material and the razor should be flooded with water, while cutting the sections.

2. Brush should be used while handling the section.

3. Coverslip should be placed gently to avoid the entry of air bubbles.

4. Remove extra glycerine with filter paper.