Plant Anatomy

(a) Differences between Dicot and Monocot Root:

Feature	Dicot Root	Monocot Root
Xylem Bundles	Usually 2 to 4 (diarch to tetrarch).	More than six (polyarch).
Cambium	Develops during secondary growth.	Absent.
Pith	Small or inconspicuous.	Large and well-developed.

(b) Differences between Dicot and Monocot Stem:

Feature	Dicot Stem	Monocot Stem
Vascular Bundles	Arranged in a ring.	Scattered throughout the ground tissue.
Bundle Sheath	Absent.	Sclerenchymatous bundle sheath present.
Phloem Parenchyma	Present.	Absent.
Pith	Present in the center.	Absent (ground tissue is undifferentiated).

One can ascertain the type of stem by looking at the arrangement and structure of vascular bundles:

• Dicot Stem: If the vascular bundles are arranged in a ring, are conjoint and open (possess cambium), and have a distinct pith in the center.
• Monocot Stem: If the vascular bundles are scattered, surrounded by a sclerenchymatous bundle sheath, and are conjoint and closed (lack cambium). Also, phloem parenchyma will be absent.

Based on the presence of scattered vascular bundles with sclerenchymatous sheaths and the absence of phloem parenchyma, the plant material is identified as a Monocotyledonous stem.

Stomatal Apparatus: It consists of the stomatal aperture, the surrounding guard cells, and the adjacent subsidiary cells.

• Guard Cells: Two specialized epidermal cells that regulate the opening and closing of the pore. They are bean-shaped in dicots and dumb-bell shaped in grasses.
• Structure: The outer walls of guard cells are thin, while the inner walls (towards the pore) are highly thickened. They contain chloroplasts.
• Subsidiary Cells: Epidermal cells near guard cells that become specialized in shape and size.

1. Epidermal Tissue System: Comprises epidermal cells, stomata, and epidermal appendages (trichomes and hairs).
2. Ground (Fundamental) Tissue System: Consists of simple tissues like parenchyma, collenchyma, and sclerenchyma. It forms the cortex, pericycle, pith, and mesophyll.
3. Vascular (Conducting) Tissue System: Comprises complex tissues, namely xylem and phloem.

The study of plant anatomy is useful for several reasons:

• Structural Organization: To understand the internal structure and functional organization of higher plants.
• Taxonomy: To distinguish between monocots and dicots and identify unknown plant materials.
• Adaptation: To understand how plants adapt to diverse environments (e.g., xerophytic adaptations).
• Economic Value: To identify wood quality, fibers, and check for adulteration in herbal medicines and commercial plant products.

A dorsiventral leaf (typically dicot) shows three main parts:

• Epidermis: Covers both the upper (adaxial) and lower (abaxial) surfaces. The abaxial epidermis generally has more stomata. A thick cuticle is present.
• Mesophyll: The tissue between the two epidermal layers. It contains chloroplasts and is differentiated into:
  • Palisade Parenchyma: Adaxially placed, made of elongated cells arranged vertically and parallel.
  • Spongy Parenchyma: Situated below palisade cells, consisting of oval or round, loosely arranged cells with large air cavities.
• Vascular System: Includes vascular bundles seen in veins and the midrib. They are surrounded by a layer of thick-walled bundle sheath cells. Xylem is usually located towards the adaxial side.