The Internal Structure of the Monocot Stem

Monocots or monocotyledons are found in grass or grass-like flowering plants, also known as angiosperms. Generally, a flowering plant is categorised based on the number of cotyledons. What fascinates us the most is the internal structure of the monocot stem. A monocot plant is defined based on the presence of a single embryonic leaf, hence the name mono. The majority of our agricultural crops fall under the monophyletic group. It comprises some of our staple crops such as corn, wheat, onion, rice, sugar cane, garlic and bamboo. Further in this article, we will see what the internal parts of the monocot stem are.

The internal structure of the monocot stem

Inside a monocot stem, we find vascular bundles near the outside edge of the stem. The parenchyma tissue is scattered with the vascular bundles. There is no pith region in the internal structure of the monocot stem. 

Now let us explore the internal parts of a monocot stem.

Epidermis

The epidermis is the outermost layer of the monocot stem that comprises a single layer of parenchyma cells packed with a thick cuticle. No epidermal outgrowths are found.

Hypodermis

The layers of sclerenchyma cells found below the epidermis layer are known as hypodermis. The hypodermis helps in providing the required mechanical strength to plants.

Ground tissue

The ground tissue consists of the many loosely packed layers of parenchyma and encloses the prominent intercellular spaces. The ground tissue is not differentiated into the epidermis, cortex, pith and pericycle. The ground tissue helps the plant in storing food.

Vascular bundles

Vascular bundles are found scattered in the layer of parenchymatous ground tissue. These are small-sized, numerous and in close arrangement with the peripheral portion of the monocot stem. 

When moved in at the centre of the vascular bundles, one can find the bundles are larger and loosely arranged. Each of the vascular bundles is found to be surrounded by a thin sheath of sclerenchymatous fibres known as the bundle sheath. In short, the vascular bundles are conjoint, collateral, closed and endarch.

Xylem and phloem also constitute the internal structure of the monocot stem.

Phloem

The phloem consists of the sieve tubes and the companion cells in a monocot stem. In the internal parts of a monocot stem, phloem fibres and phloem parenchyma are absent.

Xylem

Two vessels of the metaxylems are located at the upper two arms of the plants. In the internal structure of the monocot stem, one or two vessels of the protoxylem are present at the base in a Y shape.

The internal structure of monocot maize:

The internal structure of monocot maize has the following internal parts when a thin transverse section is taken under consideration:

1. Epiblema:

An epiblema is also known as rhizodermis which is the outermost layer of the maize root. It is a single-celled wall that comprises parenchymatous cells. It lacks the presence of stomata and cuticles. The hairy roots help absorb water and various minerals and nutrients from the depth of the soil. This layer of epiblema also protects the inner tissues of the monocot roots of maize.

2. Cortex:

The cortex is a multilayered zone that is sufficiently large, comprising parenchymatous cells and intercellular spaces. The cortex helps store water and food materials.

3. Endodermis:  

The endodermis is the innermost layer of the cortex and contains Casparian strips and cell passage. The Casparian strips are thickened band-like structures made of suberin.

4. Stele:

The tissues that lie in the innermost part of the endodermis form the stele region of the monocot roots. This innermost region includes the pericycle, the vascular tissues and the pith.

•   Pericycle: It comprises a single layer of thin-walled cells. The origination of the lateral roots takes place from this layer of pericycle.
• Vascular tissues: They consist of many patches of xylem and phloem arranged radially. The xylem is also known as exarch and polyarchy, and the sclerenchyma forms the conjunctive tissue.
•  Pith: The pith region is present at the centre of the internal structure of the monocot maize. This entire region comprises parenchymatous cells along with intercellular spaces. It helps in storing food for the plant and contains a huge amount of starch grains.

Conclusion

In conclusion, a monocot root gets the shape of a barrel when the parenchymatous tissues are arranged without any intercellular spaces. The passages of the cells are absent and there are very few Casparian stripes. In the internal structure of the monocot root, there is no secondary growth, and the lateral roots originate only from the pericycle. The vascular bundles are in a radial shape, and the xylem is exarch. The bundle count is more than six.The seeds of grass or grass-like plants containing one embryonic leaf or cotyledon are monocot stems.The ground tissue consists of the many loosely packed layers of parenchyma and encloses the prominent intercellular spaces. The ground tissue is not differentiated into the epidermis, cortex, pith and pericycle. The ground tissue helps the plant in storing food.