Internal (anatomical) structure of stem

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The internal structure of dicot and monocot stem transversely and observe it under a compound microscope.

Internal Structure of Dicot Stem (e.g., Sunflower)

The transverse section of the young sunflower stem shows the following structure;

Epidermis: outermost single layered, lack of chloroplast, multicellular hairs and stomata present, cutin layer is present outer side of epidermis called cuticle and play significant role in protection.

Cortex: consists several layers of cells and divided into three sub-zones;

  • Hypodermis: 3-4 layers of collenchyma cells contain chloroplasts and serve to mechanical or additional support,

  • Middle layer (general cortex): parenchymatous and multilayered cells and stored food,

  • Endodermis: innermost layer of the cortex, single celled thick layer, cells are barrel shaped and is rich in starch, also called as starch sheath.

Stele: all the tissues lying internal to endodermis constitute the stele.

  • Pericycle: situated between endodermis and vascular bundles, pericycle stem is multilayered and made up of sclerenchyma. Sclerenchymatous pericycle is also known as hard bast.

  • Vascular bundles: arranged in a ring, each vascular bundle is conjoint (xylem and phloem together in one bundle), collateral (xylem and phloem on the same radius with phloem towards the periphery) and open (cambium is present in between xylem and phloem). Eustele is present in dicotyledons stems.

  • Medullary rays: narrow regions of parenchymatous cells in between the vascular bundles.

  • Pith: large central part of the stem, parenchymatous cells with plenty of intercellular spaces.

Image showing T.S. of Sunflower stem.

Image Showing T.S. Of Sunflower Stem.

Image showing T.S. of Sunflower stem.

Internal Structure of Monocot Stem (e.g., Maize)

The internal structure of the young maize stem shows the following structure in a transverse section;

Epidermis: single layered with compact, living cells, covered with thick cuticle and no hairs.

Hypodermis: below epidermis and parenchymatous cells.

Ground tissue: the entire tissue lying inside the epidermis except vascular bundles is known as ground tissue and consists of rounded parenchymatous cells with distinct intercellular spaces.

Vascular bundle: scattered throughout the ground tissue, each vascular bundle is oval and usually surrounded by a sheath of sclerenchymatous cells. Each vascular bundle is conjoint, collateral and closed (no cambium strip between xylem and phloem). In xylem number of vessels is less. Vessels are arranged in V or Y shape. Phloem parenchyma is absent.

Pith: Pith is undifferentiated in monocotyledon stems. Atactostele is found in monocotyledon.

Image showing T.S. of Maize stem.

Image Showing T.S. Of Maize Stem.

Image showing T.S. of Maize stem.

Differences Between Dicot Stem and Monocot Stem

Table Showing Difference Between Dicot Stem and Monocot Stem.
Table showing difference between dicot stem and monocot stem.

Characters

Dicot stem

Monocot stem

Epidermal hairs, Endodermis

Present

Absent

Hypodermis

Collenchymatous

Sclerenchymatous

Ground tissue

Differentiated into cortex, endodermis, pericycle, pith and medullary rays

Undifferentiated

Vascular bundles

-Limited in numbers usually 4-8

-arranged in a ring

-open

-bundle sheath absent

-xylem vessels arranged in a radial row

-water cavity absent

-conjoint, collateral and open

-Numerous

-arranged in scattered

-closed

-bundle sheath present

-xylem vessels arranged in shape of letter “Y”

-water cavity present

-conjoint, collateral and closed

Secondary growth

Present

Mostly absent

Anatomical Differences Between Stem and Root

Table Showing Differences Between Stem and Root.
Table showing differences between stem and root.

Characters

stem

Root

Cuticle, stomata

Present

Absent

Hair

Multicellular

Unicellular

Hypodermis

Present

Absent

Ground Tissue

Differentiated

Differentiated

Cortex

Narrow (dicot) or undifferentiated (monocot)

Wide

Pericycle

Many layered of sclerenchymatous and parenchymatous cells

Single layered, of parenchymatous cells only

Vascular bundles

Many, conjoint and collateral

Fixed number, radial

Xylem

Endarch

Exarch