📝 Chapter Notes & Revision

Morphology of Flowering Plants

🏫 MP BoardClass 11Biology

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Quick Revision Notes: Morphology of Flowering Plants

Class: 11 | Subject: Biology (MP Board)

1. Introduction

Morphology refers to the study of external forms and features of plants. Flowering plants (Angiosperms) are characterized by the presence of roots, stems, leaves, flowers, and fruits.

2. The Root (जड़)

The root is the underground, descending portion of the plant axis.

Types of Root Systems:

  1. Tap Root System (मula जड़ तंत्र):
    • Originates from the radicle of the embryo.
    • Found in dicotyledonous plants.
    • Example: Mustard plant.
  2. Fibrous Root System (झकड़ा/रेशेदार जड़ तंत्र):
    • Primary root is replaced by a large number of roots originating from the base of the stem.
    • Found in monocotyledonous plants.
    • Example: Wheat plant.
  3. Adventitious Root System (अपस्थानिक जड़ें):
    • Roots arise from parts of the plant other than the radicle.
    • Example: Banyan tree (prop roots), Maize (stilt roots).

Regions of the Root:

  • Root Cap: Protects the tender apex of the root.
  • Region of Meristematic Activity: Cells divide rapidly; small, thin-walled with dense protoplasm.
  • Region of Elongation: Cells elongate rapidly and are responsible for root growth in length.
  • Region of Maturation: Cells differentiate and mature; root hairs absorb water and minerals here.

Modifications of Roots:

  • For Storage: Tap roots (Carrot, Turnip) and Adventitious roots (Sweet potato).
  • For Support: Prop roots (Banyan), Stilt roots (Maize, Sugarcane).
  • For Respiration (Pneumatophores): Grow vertically upward out of the soil/water (e.g., Rhizophora / Mangroves).

3. The Stem (तना)

The stem is the ascending part of the axis bearing branches, leaves, flowers, and fruits. It develops from the plumule of the embryo.

Modifications of Stem:

  • For Food Storage: Underground stems like Potato, Ginger, Turmeric, Zaminkand, Colocasia.
  • For Support/Climbing: Stem Tendrils (Cucumber, Pumpkins, Grapevines).
  • For Protection: Thorns (Citrus, Bougainvillea).
  • For Photosynthesis/Assimilation: Phylloclade (Opuntia) and Cladode (Asparagus).
  • For Vegetative Propagation: Runners, Stolons, Suckers, Offsets (e.g., Mint, Jasmine, Pistia).

4. The Leaf (पत्ती)

A leaf is a lateral, generally flattened structure borne on the stem. It develops at the node and bears a bud in its axil.

Parts of a Leaf:

  1. Leaf base: May bear two lateral small leaf-like structures called stipules.
  2. Petiole: Helps hold the blade to light.
  3. Lamina / Leaf blade: The green expanded part with veins and veinlets.

Venation (शिराविन्यास):

The arrangement of veins and the veinlet network in the lamina of a leaf.

  • Reticulate Venation: Veinlets form a network; characteristic of dicots.
  • Parallel Venation: Veins run parallel to each other; characteristic of monocots.

Types of Leaves:

  • Simple Leaf: Lamina is entire or when incised, the incisions do not touch the midrib.
  • Compound Leaf: Incisions of the lamina reach up to the midrib, breaking it into a number of leaflets.
    • Pinnately compound: Leaflets are present on a common axis, the rachis (e.g., Neem).
    • Palmately compound: Leaflets are attached at a common point, i.e., at the tip of the petiole (e.g., Silk cotton).

Phyllotaxy (पर्णविन्यास):

The pattern of arrangement of leaves on the stem or branch.

  1. Alternate: Single leaf arises at each node in alternate manner (e.g., China rose, Mustard).
  2. Opposite: A pair of leaves arise at each node and lie opposite to each other (e.g., Calotropis, Guava).
  3. Whorled: More than two leaves arise at a node and form a whorl (e.g., Alstonia).

5. The Inflorescence (पुष्pक्रम)

The arrangement of flowers on the floral axis (peduncle).

  1. Racemose: The main axis continues to grow, flowers are borne laterally in an acropetal succession (older flowers at the base, younger at the apex).
  2. Cymose: The main axis terminates in a flower, hence is limited in growth, flowers are borne in a basipetal order (older flowers at the top, younger at the base).

6. The Flower (पुष्प)

A flower is a modified shoot meant for sexual reproduction.

Symmetry:

  • Actinomorphic (Radial symmetry): Can be divided into two equal radial halves in any radial plane passing through the centre (e.g., Mustard, Datura, Chilli).
  • Zygomorphic (Bilateral symmetry): Can be divided into two similar halves only in one particular vertical plane (e.g., Pea, Gulmohur, Bean, Cassia).
  • Asymmetric (Irregular): Cannot be divided into two similar halves by any vertical plane (e.g., Canna).

Insertion of Florals Parts (Position of ovary with respect to other parts):

  1. Hypogynous: Ovary is superior; other parts lie below the ovary (e.g., Mustard, China rose, Brinjal).
  2. Perigynous: Ovary is half-inferior; thalamus forms a cup-shaped structure around it (e.g., Plum, Rose, Peach).
  3. Epigynous: Ovary is inferior; thalamus encloses the ovary completely and fuses with it, other parts arise above it (e.g., Guava, Cucumber, ray florets of sunflower).

Parts of a Flower (Whorls):

  1. Calyx (बाह्यदलपुंज): Outermost whorl, units are sepals. Protects the flower in bud stage. (Gamosepalous = united sepals; Polysepalous = free sepals).
  2. Corolla (दलपुंज): Second whorl, units are petals. Brightly coloured to attract insects for pollination.
    • Aestivation: The mode of arrangement of sepals or petals in floral bud (Valvate, Twisted, Imbricate, Vexillary).
  3. Androecium (पुमंग): Male reproductive organ, units are stamens. Each stamen consists of an anther and a filament.
  4. Gynoecium (जायांग): Female reproductive organ, units are carpels/pistils (Stigma, Style, Ovary). (Apocarpous = free carpels; Syncarpous = fused carpels).
    • Placentation: The arrangement of ovules within the ovary (Marginal, Axile, Parietal, Free central, Basal).

7. The Fruit (फल)

It is a mature or ripened ovary, developed after fertilization.

  • Parthenocarpic Fruit: Formed without fertilization (e.g., Seedless banana).
  • Structure: Consists of a pericarp (fruit wall) and seed(s). Pericarp may be dry or fleshy (epicarp, mesocarp, endocarp).

8. The Seed (बीज)

A fertilized ovule. Consists of a seed coat and an embryo.

  • Dicotyledonous Seed: Two cotyledons (e.g., Gram, Pea). Has seed coat, hilum, micropyle, cotyledons, and embryo axis (radicle and plumule).
  • Monocotyledonous Seed: One cotyledon (e.g., Maize, Wheat). Endospermic (mostly), seed coat fused with fruit wall, scutellum (single cotyledon), aleurone layer, coleoptile (plumule sheath), and coleorhiza (radicle sheath).

9. Semi-Technical Description of a Typical Flowering Plant (Family Fabaceae)

Short-hand representation using Floral Formula and Symbols:

  • Br: Bracteate
  • K: Calyx
  • C: Corolla
  • A: Androecium
  • G: Gynoecium (underline means superior ovary, bar above means inferior)
  • ⚥: Bisexual flower
  • %: Zygomorphic
  • ⨁: Actinomorphic

Important Family at a Glance: Fabaceae (Leguminosae)

  • Habit: Trees, shrubs, herbs; root nodules with Rhizobium.
  • Leaves: Pinnately compound, alternate, stipulate, pulvinate leaf base.
  • Inflorescence: Racemose.
  • Flower: Bisexual, zygomorphic.
  • Calyx: Sepals 5, gamosepalous; valvate/imbricate aestivation.
  • Corolla: Petals 5, polypetalous, papilionaceous (standard, two lateral wings, two anterior keels fused), vexillary aestivation.
  • Androecium: 10, diadelphous (9+1), anther dithecous.
  • Gynoecium: Superior ovary, bicarpellary, unilocular with many ovules, marginal placentation.
  • Fruit: Legume; Seed: Non-endospermic.
  • Floral Formula: % ⚥ K(5) C1+2+(2) A(9)+1 G_1
  • Economic Importance: Pulses (gram, arhar, moong), edible oil (soyabean, groundnut), dye (indigofera), fiber (sunhemp), fodder (sesbania, trifolium), ornamental (sweet pea, lupin).