Tissue

 

Anatomy and Primary Structure of Monocot Stem-maize Stem

The outline of the maize in transverse section is more or less circular.

 

Primary Structure of Monocot Stem-maize Stem

 

The outline of the maize in transverse section is more or less circular. The transverse section of the monocot stem [maize] shows the following plan of arrangement of tissues from the periphery to the centre.

 Epidermis

 It is the outermost layer of the stem. It is made up of single layer of tightly packed parenchymatous cells. Their outer walls are covered with thick cuticle. The continuity of this layer may be broken here and there by the presence of a few stomata. There are no epidermal outgrowths.

 Hypodermis

 A few layer of sclerenchymatous cells lying below the epidermis constitute the hypodermis. This layer gives mechanical strength to the  plant. It is interrupted here and there by chlorenchyma cells.

 Ground Tissue

 There is no distinction into cortex, endodermis, pericycle and pith. The entire mass of parenchyma cells lying inner to the hypodermis forms the ground tissue.

The cell wall is made up of cellulose. The cells contain reserve food material like starch. The cells of the ground tissue next to the hypodermis are smaller in size, polygonal in shape and compactly arranged.

Towards the centre, the cells are loosely arranged, rounded in shape and bigger in size. The vascular bundles lie embedded in this tissue. The ground tissue stores food and performs gaseous exchange.

Vascular Bundles

Vascular bundles are scattered (atactostele) in the parenchymatous ground tissue. Each  vascular bundle is surrounded by a sheath of sclerenchy-matousfibres called bundle sheath. The vascular bundles areconjoint, collateral, endarch and closed.Vascular bundles are numerous, small and closely arranged in the peripheral portion. Towards the cen-tre, the bundles are comparatively large in size and loosely arranged­. Vascular bun-dles are skull or oval shaped.

 Phloem

The phloem in the monocot stem consists of sieve tubes and companion cells. Phloem parenchyma and phloem fibres are absent. It can be distinguished into an outer crushed protophloem and an inner metaphloem.

 Xylem

 Xylem vessels are arranged in the form of ’Y’ the two metaxylem vessels are located at the upper two arms and one or two protoxylem vessels at the base. In a mature bundle, the lowest protoxylem disintegrates and forms a cavity known as protoxylem lacuna.

 

Anatomical differences between dicot stem and monocot stem

1. Hypodermis

Characters of Dicot Stem :Collenchymatous

Characters of Monocot Stem :Sclerenchymatous

2. Ground tissue

Characters of Dicot Stem : Differentiated into cortex, endodermis and pericycle and pith

Characters of Monocot Stem : Not differentiated, but it is a continuous mass of parenchyma

3. Starch Sheath

Characters of Dicot Stem : Present

Characters of Monocot Stem : Absent

4. Medullary rays

Characters of Dicot Stem : Present

Characters of Monocot Stem : Absent

5. Vascular bundles

Characters of Dicot Stem : (a) Collateral and open

Characters of Monocot Stem : (a) Collateral and closed

 Characters of Dicot Stem : (b) Arranged in a ring

Characters of Monocot Stem : (b) Scattered in ground tissue

 Characters of Dicot Stem : (c) Secondary growth occurs

Characters of Monocot Stem : (c) Secondary growth usually does not occur.

Anatomical differences between root and stem

  

 1. Epidermis 

Root : Absence of cuticle and epidermal pores.

Stem : Presence of cuticle and epidermal pores.

Root : Presence of unicellular root hairs.

Stem : Presence of unicellular and multicellular trichomes

2. Outer Cortical cells

Root :Chlorenchyma absent 

Stem :Chlorenchyma present

3. Endodermis 

Root : Well defined 

Stem : ill-defined or absent.

4. Vascular bundles

Root : Radial arrangement 

Stem : Conjoint arrangement

5. Xylem 

Root : Exarch 

Stem :Endarch

Dicot Root

Monocot Root