Preparation And Study Of T.S. Of Dicot And Monocot Roots And Stems (Primary)

Aim

To prepare a temporary stained mount of a transverse section of dicot and monocot stem and root to study various plant tissues.

Material Required

• Preserved material of sunflower root and stem
• Preserved or fresh material of maize root and stem
• Microscope
• Sharp blade
• Slides
• Watch glass
• Coverslips
• Safranin (1gm in 100ml of 50% ethanol)
• Brush
• Glycerine
• Blotting paper

Diagram

T.S Of Dicot Stem

T.S Of Monocot Stem

Procedure

Taking Sections

• Hold the dissected plant material between your index finger and thumb, while keeping the edge of the razor perpendicular to the longitudinal axis of the plant. Slice it into thin sections.
• Using the edge of the blade, shift these sections into a watch glass with the help of a brush. The watch glass must hold water.

Process Of Staining

• Pick 2 to 4 thin and good transverse sections. Shift it to a different watch glass holding safranin stain.
• Let the complete set rest in the stain for a couple of minutes.
• After a while, drain the sections of the stain and rinse again with water so as to wash off the excess strain.

Mounting

• On a clean slide, place a stained section in the middle of the slide, mounting water or glycerine.
• Using a needle slowly places the coverslip.
• An excess of water or glycerine from the edge of the coverslip can be removed by placing blotting paper.
• Ensure, that the air bubbles are not formed while mounting.

Precautionary Measures

• While dissecting the section, both the blade and the material should be supplied with adequate water.
• While working with sections, use a brush.
• Gently place the coverslip in order to avoid air bubbles.
• Excess glycerine can be removed with filter paper.

Aim

To study the transverse section of a dicot stem, a sunflower stem.

Theory

• A typical example of a dicot stem is a sunflower
• The outline of the stem in the transverse section is circular with a hairy surface
• The transverse section depicts the arrangement of different tissues in a particular way from the exterior to the centre as listed below:

1. • Epidermis
     • It is the outermost covering of the stem and is single-layered
     • The cells are living cells that are densely arranged with a thin wall, enclosed in a cuticle
     • It displays multicellular hair
     • Function – It provides protection
   • Cortex
     • Located just under the epidermis
     • It consists of the following regions – Hypodermis, Endodermis, General cortex.

(a) Hypodermis – It is situated just below the epidermis and consists of 4 to 5 layers of collenchymatous cells. These are cells that have the cellulose deposits on the edges and are living cells. It may possess chloroplast and hence carry out photosynthesis.

Function: It renders mechanical support

(b) Endodermis – Forms the interior most covering of the cortex consisting of a singular row of cells that are densely arranged and barrel-shaped with no intercellular spaces. They are composed of starch grains.

(c) General Cortex (Parenchyma) – Located just under the hypodermis, it consists of several layers of cells that are living having thin walls along with intercellular spaces. It may contain chloroplast and hence becomes photosynthetic. Several mucilaginous canals can also be observed. Function: Food storage

1. • Stele

In tissue, it forms the central core having a vascular bundle. It comprises of – pericycle, vascular bundles, medullary rays, and pith.

(a) Pericycle

1. 1. • Located between the vascular bundles and endodermis.
      • Has recurrent patches of parenchyma and sclerenchyma.
      • Each sclerenchyma patch is linked with hard-blast fires.

(b) Medullary rays

1. 1. • It is located in the gaps between the vascular bundles. This gap finds parenchymatous cells that are thinly walled and arranged radially in 4-5 rows.
      • Helps in the storage of food material and in the lateral conduction of water and food.

(c) Vascular bundle

1. 1. • They are open, collateral and conjoint and are set up in a ring-like manner.
      • Each of the vascular bundle comprises of- xylem, phloem, cambium.
      • Phloem is located below the pericycle towards the exterior side. It consists of thin cell walls possessing companion cells, sieve tube and phloem parenchyma and conducts food material.
      • Xylem is found in the interior of the vascular bundle, i.e., smaller protoxylem towards the centre and larger metaxylem towards the periphery. Therefore xylem is endarch. These cells are dead and lignified. Xylem conducts minerals and water.
      • The cambium is present between phloem and xylem. The cells are rectangular and have thin cell walls. It consists of meristematic tissues that generate new cells.

(d) Pith

1. 1. • It forms the mid-region of the stem. It arises under the vascular bundle up till the centre and consists of large parenchymatous cells.

T.S. of Dicot Stem – Sunflower Stem

Identification

• The epidermis has multicellular hairs.
• The hypodermis is collenchymatous.
• The xylem is endarch with the protoxylem being at the centre and the metaxylem being at the periphery.
• Vascular bundles are open, collateral and conjoint.
• They are arranged in a ring-like manner.
• Pith is found at the centre.

Conclusion

The specimen provided is a section of a dicot stem.

Aim

To study the transverse section of the dicot root, sunflower root.

Theory

The T.S shows the following structures:

1. 1. Epiblema or Epidermis
      • Densely arranged cells with thin cell walls forming the outermost single layer
      • Several cells have thin outgrowths known as root hairs
   2. Cortex
      • Present under the epidermis consisting of several layers of thin-walled parenchyma cells
   3. Endodermis
      • They are barrel-shaped forming the innermost layer of the cortex. They are densely arranged single cell layer.
      • A Casparian band is formed due to the radially arranged cell walls that are thickened
   4. Pericycle
      • Under the endodermis is a thin-walled layer of cells known as pericycle.
   5. Vascular bundles
      • It consists of radial bundles having alternating 2 to 6 arrangement of bundles of phloem and xylem
      • Bundles of xylem are exarch wherein the metaxylem is present towards the center and the protoxylem at the outer side
      • In outline, xylem vessels are polygonal
   6. Phloem bundles
      • Comprises of companion cells, parenchyma and sieve tube
   7. Conjunctive tissue
      • They are the parenchyma cells that separate the xylem and phloem bundles from each other
   8. Pith
      • They are significantly absent or occur rarely

T.S. of Dicot Root – Sunflower Root

Identification

1. 1. • The epidermis shows the presence of unicellular hair
      • Absence of hypodermis
      • Radially arranged vascular bundles
      • The number of phloem/xylem bundles is not more than 6
      • The xylem is an exarch
      • Absence or rare occurrence of pith

Conclusion

The specimen provided is a section of the dicot root.

Aim

To study the transverse section of monocot stem, maize stem.

Theory

1. 1. • The maize plant is a monocot plant
      • The transverse section is circular having a smooth surface
      • The ground tissue consists of many scattered vascular bundles
      • From the periphery to the center, the transverse section displays the structure of different tissues in a particular manner as follows:
      1. Epidermis
         • An outermost, single layer
         • Thin-walled cells that are living. Presence of thick cuticle towards the outermost surface
         • The rare occurrence of stomata.
         • Lack of epidermal hair
         • Function – Protection of internal tissue
      2. Hypodermis
         • Present under the epidermis
         • Consists of the thick-walled dead layer of sclerenchymatous cells. Made up of two of these three layers
      3. Ground Tissue
         • Found below the hypodermis
         • Consists of thin-walled living cells, parenchymatous cells
         • Loose arrangement of cells with the presence of intercellular spaces
         • As seen in the dicotyledonous stem, there is no differentiation of cortex, pericycle and the endodermis
      4. Vascular bundles
         • Several scattered vascular bundles found in the ground tissue and are closed type, collateral and conjoint
         • At the periphery, the vascular bundles are more and densely arranged when compared to the center
         • Large vascular bundles in the center compared to vascular bundles at the periphery
         • They resemble an oval shape that is girdled by sclerenchymatous bundle sheath
         • It consists of the xylem and the phloem

(a) Xylem

1. 1. 1. • Y-shaped
         • Metaxylem are present at the two lateral arms. Protoxylem is present at the base
         • The lower protoxylem particles form a cavity known as lysogenous cavity
         • Function: Conducts water

(b) Phloem

1. 1. 1. • Present at the periphery and consists of living cells
         • It comprises of companion cells, sieve tubes, and the phloem parenchyma
         • Function – Conducts food material

T.S of monocot stem – Maize stem

Conclusion

The specimen provided is a section of the monocot stem.

Aim

To study of the transverse section of monocot root, maize root.

Theory

The transverse section of monocot root depicts the structures as listed below:

1. 1. 1. Epiblema or Epidermis
         • It is a single outermost layer with no cuticle
         • Densely arranged cells
         • Few cells may see unicellular root hair emerging
      2. Cortex
         • Found below epidermis
         • It is broad consisting of multiple layers of parenchyma cells
      3. Endodermis
         • The innermost layer of the cortex
         • Barrel-shaped cells arranged in a ring-like manner
         • Presence of Casparian bands
      4. Pericycle
         • Found below the endodermis and is a single layer of parenchymatous cells
      5. Vascular bundles
         • There are 8 or more alternating bundles of phloem and xylem known as radial bundles
         • Xylem bundles are exarch
         • Xylem bundles are oval or rounded
         • Phloem is found under the pericycle and comprises of companion cells, sieve tube, parenchyma
      6. Conjunctive tissue
         • It is the xylem and phloem bundles that are distinguished from each other by the parenchyma tissue
      7. Pith
         • Well developed pith is observed
         • It comprises of the parenchyma in the mid-region of the root

Identification

1. 1. • Epidermis sees the presence of unicellular hair
      • Absence of hypodermis
      • Radially arranged vascular bundles
      • 8 or more than 8 phloem and xylem bundles
      • A well-developed pith

T.S of monocot root – Maize root

Conclusion

The specimen provided is a section of the monocot root.

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