MORPHOLOGY OF FLOWERING PLANTS

Morphology (Gr. Morphos = Form; logos = Study) is the branch of science which deals with the study of form and structure. In botany, it generally means the study of external features, forms and relative positions of different organs on plants.

Different parts of a flowering plant are –

  • THE ROOT

Roots are developed from radicle of the embryo of a germinating seed.

In majority of the dicotyledonous plants, the direct elongation of the radicle leads to the formation of primary root which grows inside the soil. It bears lateral roots of several orders that are referred to as secondary, tertiary, etc. roots. The primary roots and its branches constitute the tap root system.

e.g., mustard plant.

In monocotyledonous plants, the primary root is short lived and is replaced by a large number of roots. These roots originate from the base of the stem and constitute the fibrous root system.

e.g., wheat plant.

In some plants, like grass, Monstera and the banyan tree, roots arise from parts of the plant other than the radicle and are called adventitious roots.

The main functions of the root system are –

Absorption of water and minerals from the soil                                                          Providing a proper anchorage to the plant parts     Storing reserve food material       Synthesis of plant growth regulators.

  • THE STEM

The stem develops from the plumule of the germinating seed.

The stem shows the differentiation of nodes and internodes.

The place where the leaf develops on the stem is called the node.

The portion of the stem between two successive nodes is called the internode.

 

    

 

  • THE LEAF

The leaf is a lateral, generally flattened structure borne on the stem.                           It develops exogenously at the node and bears a bud in its axil – the axillary bud, which later develops into a branch.                                                                                  Leaves originate from shoot apical meristems and are arranged in an acropetal order.                   They are the most important vegetative organs for photosynthesis.

Characteristics of leaf

(i) The leaf is a lateral dissimilar appendage of the stem.

(ii) A leaf is always borne at the node of stem.

(iii) Generally there is always an axillary bud in the axil of a leaf.

(iv) It is exogenous in origin and develops from the swollen leaf primordium of the growing apex.

(v) The growth of leaf is limited.

(vi) The leaves do not possess any apical bud or a regular growing point.

(vii) A leaf has three main parts – Leaf base, petiole and leaf lamina. In addition, it may possess two lateral outgrowths of the leaf base, called stipules.

(viii) The leaf lamina is traversed by prominent vascular strands, called veins.

 

A typical leaf consists of three main parts:

Leaf base – The leaf is attached to the stem by the leaf base and may bear two lateral small leaf like structures called stipules.                                                                            In monocotyledons, the leaf base expands into a sheath covering the stem partially or wholly – Sheathing leaf base.                            In some leguminous plants the leaf base may become swollen – Pulvinus leaf base.

Petiole – The petiole helps hold the blade to light. Long thin flexible petioles allow leaf blades to flutter in wind, thereby cooling the leaf and bringing fresh air to leaf surface.

Lamina – The lamina or the leaf blade is the green expanded part of the leaf with veins and veinlets. There is, usually, a middle prominent vein, which is known as the midrib. Veins provide rigidity to the leaf blade and act as channels of transport for water, minerals and food materials.                                                                                     Venation                                                                                                                               The arrangement of veins and the veinlets in the lamina of leaf is termed as venation.                                                                                                                         Reticulate venation – When the veinlets form a network. e.g., Dicotyledons.                      Parallel venation – When the veins run parallel to each other within a lamina. e.g., Monocot.                                                                                                                                   Types of Leaves                                                                                                                    Simple leaf – when lamina of a leaf is entire or when incised, the incisions do not touch the midrib.                                                                                                              Compound leaf – When the incisions of the lamina reach up to the midrib breaking it into a number of leaflets, the leaf is called compound.                                                             The compound leaves may be of two types – Pinnately compound leaf – a number of leaflets are present on a common axis, the rachis, which represents the midrib of the leaf. e.g., neem.                                                                                                             Palmately compound leaves – the leaflets are attached at a common point, i.e., at the tip of petiole. e.g., Silk cotton.

  • THE FLOWER

 

The flower is the reproductive unit in the angiosperms. It is meant for sexual reproduction. A typical flower has four different kinds of whorls arranged successively on the swollen end of the stalk or pedicel, called thalamus or receptacle.

These are calyx, corolla, androecium and gynoecium.

Calyx and corolla are accessory organs, while androecium and gynoecium are reproductive organs. Each flower normally has four floral whorls, viz., calyx, corolla, androecium and gynoecium.

  1. Calyx (Sepals) –

    • The calyx may be gamosepalous (sepals united) or polysepalous (sepals free).

    • Generally, sepals are green, leaf like and protect the flower in the bud stage.

    • outermost whorl of the flower.

  2. Corolla (petals) –

    • Petals are usually brightly coloured to attract insects for pollination.

    • Corolla may be also free (gamopetalous) or united (polypetalous).

    • The shape and colour of corolla vary greatly in plants. Corolla may be tubular, bell-shaped, funnel-shaped or wheel-shaped.

  3. Androecium (Stamens) –

    • Represents the male reproductive organ.

    • Each stamen consists of a stalk or a filament and an anther.

    • Each anther is usually bilobed and each lobe has two chambers, the pollen-sacs.

    • The pollen grains are produced in pollen-sacs.

    • A sterile stamen is called staminode.

    • When stamens are attached to the petals, they are called epipetalous.             e.g., brinjal.

    • When stamens are attached to the perianth, they are called epiphyllous.       e.g., lily.

    • Fusion of stamen –

      • If the stamens in a flower remain free – Polyandrous.

      • If the stamens are united into one bundle – monoadelphous. e.g., china rose.

      • If the stamens are united into two bundles – diadelphous. e.g., pea.

      • If the stamens are united into more than two bundles – Polyadelphous. e.g., citrus.

    • There may be a variation in the length of filaments within a flower, as in Salvia and mustard.

  4. Gynoecium (Carpels/Pistils) –

    • Gynoecium is the female reproductive part of the flower.

    • A carpel consists of three parts – stigma, style and ovary.

      • Ovary is the enlarged basal part, on which lies the elongated tube, the style.

      • The style connects the ovary to the stigma.

      • The stigma is usually at the tip of the style and is the receptive surface for pollen grains.

Each ovary bears one or more ovules attached to a flattened, cushion-like placenta.

 

  • AESTIVATION