Table of contents | |
Dicotyledonous Root | |
Monocotyledonous root | |
Dicotyledonous Stem | |
Monocotyledonous Stem | |
Dorsiventral (Dicotyledonous) Leaf | |
Isobilateral (Monocotyledonous) Leaf |
For a clearer understanding of how tissues are organized in the roots, stems, and leaves of plants, it is helpful to examine the transverse sections (cross-sections) of the mature regions of these organs.
Plants are broadly classified into two categories based on the number of cotyledons (seed leaves) in their seeds:
By studying the transverse sections of the mature roots, stems, and leaves of dicots and monocots, we can observe the differences in tissue organization and structure between these two groups of plants.
Dicot Root
Monocotyledonous roots have a similar structure to dicot roots, including features like the epidermis, cortex, endodermis, pericycle, vascular bundles, and pith.
Monocot Root
In a typical young dicotyledonous stem, the transverse section reveals various distinct features:
Dicot Stem
Monocot Root
Epidermis: The epidermis covers both the upper (adaxial) and lower (abaxial) surfaces of the leaf and has a noticeable cuticle.
The abaxial epidermis usually has more stomata than the adaxial epidermis, which may even lack stomata.
Mesophyll: The mesophyll, located between the upper and lower epidermis, contains chloroplasts and is responsible for photosynthesis.
Dicot Leaf
It is made up of parenchyma tissue and consists of two types of cells:
(a) Palisade Parenchyma: These are elongated cells arranged vertically and parallel to each other, located just below the upper epidermis.
(b) Spongy Parenchyma: These oval or round cells are loosely arranged and situated below the palisade cells, extending down to the lower epidermis. There are large air spaces and cavities between these cells.
Vascular System: The vascular system includes vascular bundles found in the veins and midrib of the leaf.
(a) The size of the vascular bundles depends on the size of the veins, which vary in thickness in the reticulate venation of dicot leaves.
(b) The vascular bundles are surrounded by a layer of thick-walled bundle sheath cells.
(c) In the vascular bundles, the xylem is positioned in the upper part.
The anatomy of isobilateral leaf is similar to that of the dorsiventral leaf in many ways. It shows the following characteristic differences.
Monocot Leaf
Stomata: In isobilateral leaves, stomata are present on both surfaces of the epidermis.
Mesophyll: The mesophyll in isobilateral leaves is not differentiated into palisade and spongy parenchyma.
Bulliform Cells: In grasses, certain adaxial epidermal cells along the veins modify into large, empty, colorless bulliform cells. These cells play a crucial role in water regulation.
Water Regulation: When bulliform cells are turgid (full of water), they help expose the leaf surface. Conversely, when they are flaccid (due to water stress), they cause the leaves to curl inward to minimize water loss.
Venation: The parallel venation in monocot leaves is reflected in the similar sizes of vascular bundles (except in main veins) observed in vertical sections of the leaves.
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1. What are the main differences between dicotyledonous and monocotyledonous roots? |
2. How can you differentiate between dicotyledonous and monocotyledonous stems? |
3. What structural features are characteristic of a dorsiventral dicotyledonous leaf? |
4. What are the key characteristics of an isobilateral monocotyledonous leaf? |
5. Why is understanding the anatomy of monocot and dicot plants important? |
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