Anatomy of Dicotyledonous and Monocotyledonous Plants

Monocotyledonous plants (monocots) and dicotyledonous plants (dicots) are angiosperms or flowering plants. Angiosperms are categorised based on the number of cotyledons. Cotyledon is the leaf in a seed plant that is present in its embryonic stage. The plants containing one cotyledon are monocots, and those with two cotyledons are dicots. The anatomy of dicotyledonous and monocotyledonous plants deals with the study of their structure. 

Monocot plant

• Roots: They have adventitious roots where many lateral roots arise from the base of the plant. The epidermis is the outermost layer followed by the cortex, pericycle, endodermis, vascular bundles and the pith.

Vascular bundles include the xylem and the phloem. Monocots cannot have more than six xylem. Secondary growth, like the formation of cambium, is absent.

• Stem: Even the stem of monocot plants lacks secondary growth and is hollow from the inside. The stem of monocot plants resembles that of dicot plants barring a few differences.

In monocots, the hypodermis of the cortex comprises sclerenchyma cells. The vascular bundles are present in large numbers and generally scattered and conjoint; i.e., the xylem and phloem are present on the same radius.

The vascular bundles are closed and surrounded by ground tissue consisting of parenchyma, collenchyma and sclerenchyma.

• Leaf: They have parallel venation. Both the top and the bottom sides of the leaf have stomata. Palisade parenchyma and spongy parenchyma of the leaves present in the mesophyll cells are not differentiated. The upper surface of leaves has epidermal cells and veins from which bulliform cells are developed. Bulliform cells are large and contain a void. These cells play an important role in preventing water loss by curling the leaves.

Dicot plant

• Root: The roots of a dicot plant are present in a tap root system; it has one main root from which many lateral roots arise. The outermost layer is the epidermis, followed by a cortex, endodermis and the pericycle.

Next to the pericycle, a few layers of parenchyma cells are present. The pith, which is located in the centre, is not distinct, and the xylem and phloem can be between 2 to 4 in number.

The xylem and phloem cells are surrounded by a layer of parenchyma cells known as conjunctive tissue. Secondary growth is seen in dicot plants. A layer of cambium is formed, which separates the xylem and phloem. A stele is formed by the fusion of pericycle, vascular bundles and the pith.

• Stem: The epidermis forms the outermost layer but is surrounded by a coating of wax known as the cuticle. The epidermis also contains trichomes and very less stomata.

The cortex of the dicot stems is multilayered and present in between the epidermis and the pericycle. The cortex is subdivided into three regions. The outermost region is the hypodermis, made up of collenchymatous cells. The middle layer, known as the cortical layer, comprises parenchymatous cells. The innermost layer is known as the endodermis.

Followed by endodermis, the pericycle is present. The vascular bundles are present in circular form in dicot stems only and are conjoint. The pith present in the dicot stem comprises parenchyma cells.

• Leaf: Dicot leaves show reticulate venation. Lamina is a flat area in the plant which consists of the epidermis, mesophyll cells and the vascular system. The epidermis, the outermost layer, is covered by cuticles to prevent water loss.

The abaxial epidermis, that is the epidermal cells present on the lower surface, has more stomata than the adaxial epidermis, the epidermal cells present on the upper surface. Sometimes the adaxial epidermis lacks stomata.

The mesophyll made up of parenchyma cells is composed of the palisade and spongy parenchyma and is present between the upper and lower epidermis. The mesophyll cells of leaves also contain chloroplast, which plays a vital role in photosynthesis. The vascular bundles present are surrounded by bundle sheath cells and also form the veins and midrib of the leaf.

Conclusion

Plants are vital as they provide us with food, maintain the oxygen concentration in the environment and remove harmful carbon dioxide from the atmosphere. Plants can perform all these functions due to their specific anatomy. In other words, plants can perform these functions due to the different structures and organs present.

Plants with seeds are angiosperms, and those without seeds are gymnosperms. The angiosperms are further divided into monocots and dicots. Monocot plants have one cotyledon and dicots have two cotyledons.

The anatomy of a few plant parts is a bit different in monocot and dicot plants. For instance, the roots of monocot plants do not have secondary growth like cambium, but the roots of dicot plants show secondary growth.