Anatomy of Flowering Plants

Anatomy is the study of internal structure of plants. A group of cells having a common origin and performing a common function is called a tissue.

Specialised regions of active cell division.

• Apical Meristem: Tips of roots and shoots. Produces primary tissues (Primary growth). Axillary bud formation.
• Intercalary Meristem: Between mature tissues (e.g., Grasses). Regeneration of grazed parts. Primary meristem.
• Lateral Meristem: Occurs in mature regions. Cylindrical. Responsible for Secondary growth (increase in girth). E.g., Vascular cambium, Cork cambium.

• Parenchyma:
  Living, thin-walled (cellulose), isodiametric. Major component. Functions: Photosynthesis, Storage, Secretion.
• Collenchyma:
  Living, thickened at corners (cellulose, hemicellulose, pectin). No intercellular spaces. Provides mechanical support to growing parts (young stem, petiole).
• Sclerenchyma:
  Dead, thick-walled (lignin), narrow lumen, pits.
  • Fibres: Elongated, pointed.
  • Sclereids: Spherical/oval (Stone cells in Pear/Sapota pulp). Mechanical support.

Xylem (Water conduction)

• Tracheids: Elongated, dead, lignified, tapering ends. Main element in Gymnosperms.
• Vessels: Long tube, dead, lignified, perforated end walls. Characteristic of Angiosperms (Absent in Gymnosperms).
• Xylem Fibres: Dead, support.
• Xylem Parenchyma: Living, stores food (starch/fat), radial conduction of water.

Phloem (Food conduction)

• Sieve Tube Elements: Long, tube-like, perforated end walls (sieve plates). Elements lack nucleus; controlled by Companion cell nucleus.
• Companion Cells: Specialized parenchyma, help maintain pressure gradient in sieve tubes.
• Phloem Parenchyma: Living, storage. Absent in most Monocots.
• Phloem Fibres (Bast): Dead (Sclerenchymatous). E.g., Jute, Flax, Hemp.

• Epidermal: Epidermis, Stomata, Trichomes (Stem hairs - multicellular), Root hairs (Unicellular).
• Ground: All tissues except epidermal and vascular. Parenchyma (Cortex, Pericycle, Pith, Medullary rays) + Mesophyll in leaves.
• Vascular: Xylem + Phloem.
  • Radial: Xylem and Phloem on different radii (Roots).
  • Conjoint: Xylem and Phloem on same radius (Stem, Leaves). - Open: Cambium present (Sec. growth possible - Dicots). - Closed: Cambium absent (No sec. growth - Monocots).

A. Roots

B. Stem

C. Leaf

Growth in girth due to lateral meristems.

• Ring formed by intrafascicular + interfascicular cambium.
• Cuts off Sec Xylem (towards inside) and Sec Phloem (towards outside). More xylem than phloem.
• Spring Wood (Early): Broad vessels, low density (Active cambium).
• Autumn Wood (Late): Narrow vessels, high density (Less active).
• Heartwood: Central, dark, dead, hard, durable (Tannins/Resins). Non-conducting.
• Sapwood: Peripheral, light, living. Conducts water.

• Develops in cortex. Cuts off Cork (Phellem - Dead, Suberin) outside and Sec Cortex (Phelloderm - Living) inside.
• Bark: All tissues exterior to vascular cambium (Periderm + Sec Phloem).
• Lenticels: Lens-shaped openings in periderm for gas exchange.

A group of cells having a common origin and performing a common function (Strasburger).

Occurs at tips of roots and shoots. produces primary tissues resulting in Primary Growth (length).

Occurs between mature tissues (e.g., in Grasses). Helps regenerate parts removed by grazing herbivores.

Occurs in mature regions. Responsible for Secondary Growth (girth). E.g., Vascular and Cork Cambium.

Major component of organs. Thin-walled (cellulose), living, isodiametric. Storage, Photosynthesis, Secretion.

Living mechanical tissue. Thickened at corners (Cellulose, Hemicellulose, Pectin). E.g., Petiole of dicots.

Dead mechanical tissue. Thick-walled (Lignin). Fibres (Elongated) + Sclereids (Spherical/Stony).

Found in fruit walls of nuts, pulp of fruit like Guava, Pear, Sapota (gritty texture).

Elongated, dead cells with tapering ends. Main water conducting elements in Gymnosperms.

Presence of vessels is a characteristic feature of Angiosperms. Absent in most Gymnosperms.

Long tube-like. End walls perforated (Sieve plates). Mature element lacks a nucleus.

Specialized parenchyma cells connected to sieve tubes. Help maintain pressure gradient.

Phloem fibres (Bast) are made of Sclerenchyma. Used commercially (Jute, Flax, Hemp).

Living storage cells. Generally ABSENT in most Monocotyledons.

Stomatal aperture + Guard cells + Subsidiary cells = Stomatal Apparatus.

In grasses (monocots), guard cells are dumb-bell shaped. In dicots, they are bean-shaped.

Epidermal hairs on stem are multicellular (Trichomes), help prevent water loss. Root hairs are unicellular.

Cambium present between Xylem and Phloem. Capable of secondary growth. Characteristic of Dicot stem.

Cambium absent. No secondary growth. Characteristic of Monocots.

Xylem and phloem arranged on different radii. Characteristic of Roots.

Found in Endodermis of roots. Waxy material suberin deposition. Impervious to water.

Initiates Lateral roots and Vascular cambium during secondary growth.

Monocot roots usually have more than six (polyarch) xylem bundles. Dicots have 2-4.

All tissues on the inner side of the endodermis (Pericycle + V.B. + Pith) constitute the Stele.

In Monocot Stem, vascular bundles are surrounded by Sclerenchymatous bundle sheath.

Water containing cavities are present within the vascular bundles of Monocot stem.

Dicot leaf. Stomata more on lower surface. Mesophyll diff. into Palisade and Spongy parenchyma.

Monocot leaf. Stomata equal on both sides. Mesophyll undifferentiated.

Large, empty cells in adaxial epidermis of grasses. Turgid = Leaf open. Flaccid = Leaf curls (reduce water loss).

In dicot stems, intrafascicular cambium + interfascicular cambium form a complete ring.

Cambium cuts off more cells towards inside (Sec Xylem) than outside (Sec Phloem).

Early wood. Cambium very active. Produces many vessels with wider cavities.

Late wood. Cambium less active. Fewer vessels with narrow vessels. Higher density.

Two kinds of woods (Spring + Autumn) appearing as concentric rings. Used to estimate age of tree.

Central, dark, hard, durable region. Deposition of tannins/resins/oils. Dead & Non-conducting.

Peripheral region. Lighter in color. Living. Conducts water from root to leaf.

Cork Cambium. Secondary lateral meristem usually developing in cortex region.

Cork. Formed outer to phellogen. Dead cells with suberized cell walls. Impervious to water.

Secondary Cortex. Formed inner to phellogen. Parenchymatous (living).

Phellogen + Phellem + Phelloderm = Periderm.

All tissues exterior to the vascular cambium. Includes Periderm and Secondary Phloem.

Lens-shaped openings on stem permitting gaseous exchange. Formed by action of phellogen.

Vascular cambium is completely secondary in origin (from Pericycle and tissue below phloem).

Elongated, vertically arranged, parallel cells on adaxial (upper) side of dicot leaf.

Oval/round, loosely arranged cells with air spaces on abaxial (lower) side of dicot leaf.

Protoxylem lies towards pith (center). Characteristic of Stems.

Protoxylem lies towards periphery. Characteristic of Roots.

Lacks Sieve tubes and Companion cells. Has Albuminous cells and Sieve cells.

Balloon-like extensions of parenchyma cells into lumen of vessels, blocking them (Heartwood).

Inactive region in root meristem between root cap and active meristem. Low DNA/RNA/Protein.