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CHAPTER: 5 morphology of flowering plants. Morphology:. Deals with the study of external structure. In plants morphology is characterised by presence of roots, stems, leaves, flowers and fruits. THE ROOTS:
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Morphology: • Deals with the study of external structure. In plants morphology is characterised by presence of roots, stems, leaves, flowers and fruits.
THE ROOTS: • In dicotyledons generally the radical will give rise to primary root that grows inside the soil. Primary roots bear lateral roots called secondary, tertiary etc roots. The primary roots and its branches constitute tap root system. E.g. Mustard plant.
In monocotyledons the primary root is short lived and is replaced by a large number of roots. These roots originate from the base of the stem. This type of root is called fibrous root system. E.g. Wheat plant. • In some plants (Monstera, banyan), roots arise from parts of the plant other than radical. Such roots are called adventitious root.
FUNCTION OF ROOT: • Absorption of water and minerals from the soil. • Provide proper anchorage to the plant parts. • Storage of reserve food materials. • Synthesis of plant growth regulators.
REGIONS OF THE ROOTS: • Apical region of root is covered by thimble like structure called root cap • Root cap helps in protection of tender apex of the root as it makes its way through the soil. • Above the root cap (few mm) there is region of meristematic activity.
The cells of meristematic region are very small thin walled with dense protoplasm. They are in a state of continuous division. • Above the region of meristematic activity there is a region of elongation. The cells of this region undergo rapid elongation and enlargement, thus responsible for growth of the root in length.
The cells of the elongation zone gradually differentiate and mature which is called as region of maturation. Some epidermal cells of this region forms very fine and delicate thread like structures called root hairs. Root hairs absorb water and minerals from the soil.
MODIFICATION OF ROOT: Roots in some plants are modified to perform additional functions: • Storage of food: Carrot, turnip, sweet potato. • Prop root: Supporting root in Banyan tree. • Stilt root: Supporting root in maize, sugar cane. • Pneumatophores: Respiratory roots in Rhizophora ( present in swampy area)
THE STEM • Ascendingpart bearing branches, leaves, flowers and fruits. • Develops from plumule of the embryo. • Bears nodes and internodes. • Nodes are the regions where leaves are born. • The portion between two nodes is called internode.
Stem bears buds (terminal or axillary). • Generally green when young but become woody and dark brown later on. • It helps in spreading out branches bearing leaves, flowers and fruits. • It helps in conduction of water and minerals as well as food. • Some stems perform additional functions like storage of food, support, protection, vegetative propagation.
MODIFICATION OF STEMS • Storage of food: Underground stems of potato, ginger, turmeric, zaminkand, colocasia. • Perennation: Underground stems of potato, ginger, turmeric, zaminkand, colocasia. • Tendril: Develop from axillary buds are slender and spirally coiled and help plants to climb. E.g. cucumber, pumpkins, watermelon, grapevines etc.
Thorns: Axillary buds also modified into woody straight and pointed thorns that helps in protection from browsing animals. E.g. Bougainvillea, citrus etc. • Photosynthetic: Stems modified into flattened or fleshy cylindrical structures that contain chlorophyll and carry out photosynthesis. • Spread: Grass and straw berry. • Vegetative propagation: Mint, jasmine etc.
THE LEAF • A lateral, generally flattened structure borne on the stem. • It develops at the node and bears a bud in its axil. • The axillary bud later on develops into a branch. • Leaves originate from shoot apical meristems and are arranged in an acropetal order. • Vegetative organ for photosynthesis.
PARTS OF LEAF • There are three main parts: leaf base, petiole and lamina. • The leaf is attached to the stem by the leaf base and may or may not bear two lateral small leaf like structures called stipules. • In monocots the leaf base expands into a sheath covering the stem partially or wholly.
In some leguminous plants the leaf base may become swollen (pulvinus). • Petiole helps in holding the lamina to light. Long, thin flexible petioles allow leaf lamina to flutter in wind that helps in cooling of leaf and bringing fresh air to leaf surface. • The lamina is the green expanded part of the leaf with veins and vein lets. There is a middle prominent vein called midrib.
Veins provide rigidity to the leaf blade and act as channels of transport of water, minerals and food materials. • The shape, margin, apex, surface and extent of incision of lamina varies in different leaves.
VENATION: • It is the arrangement of veins and the vein lets in the lamina of leaf. • When the vein lets form a net work, the venation is termed as reticulate (dicot). • When the veins run parallel to each other within the lamina, the venation is parallel (monocot).
Types of Leaves • Simple Leaf – Lamina is entire or if incised does not touch the midrib. • Compound Leaf- Incision of lamina reaches the midrib, forms number of leaflets and rachis.
TYPES OF COMPOUND LEAF • Pinnately compound: A number of leaf lets are present on a common axis the rachis, which represents the midrib of the leaf. E.g. neem. • Palmately compound: The leaf lets are attached at a common point i.e. at the tip of petiole. E.g. silk cotton.
PHYLLOTAXY • Arrangement of leaves on the stem or branch is called phyllotaxy. It is of alternate, opposite or whorled. • Alternate: Single leaf arises at each node in alternate manner. E.g. China rose. • Opposite: A pair of leaves arise at a node and opposite to each other. E.g. Calotropis, guava etc. • Whorled: More than two leaves arise at a node and form a whorl. E.g. Alstonia.
MODIFICATION OF LEAVES • Tendril: For climbing (peas) • Spine : For defense (cactus) • Storage of food: Fleshy leaves of onion and garlic. • Leaves of certain insectivorous plants (pitcher plant, venus-fly trap) are also modified leaves. • Reduced leaves: In Australian acacia the leaves are small and short lived. In this case the petioles expands and become green to perform photosynthesis.
TENDRIL SPINE STORAGE
THE INFLORESCENCE • The arrangement of flowers on the floral axis. • Two major types- racemose and cymose • There are some special types also. • Racemose: The main axis continues to grow, the flowers are borne laterally in an acropetal succession. • Cymose: The main axis terminates in a flower, hence is limited in growth. The flowers are borne in a basipetal order.
FLOWER • Reproductive part of the plant. • A typical flower has four different kinds of whorls arranged successively on the swollen end of the stalk or pedicel, called thalamus or receptacle. Four parts are calyx, corolla, Androecium and gynoecium. • Calyx and corolla : Accessory whorls. • Androecium and gynoecium : Reproductive and essential whorls.
In some flowers (lily) the calyx and corolla are not distinct and are called Perianth. (tepals) • When a flower has both androecium and gynoecium it is called bisexual flower. • A flower having either only androecium (stamen) or only gynoecium (carpel) is unisexual. • The flower may be actinomorphic (radial symmetry) or zygomorphic (bilateral symmetry).
Actinomorphic flower: A flower can be divided into two equal halves in any radial plane passing through the centre. E.g. Mustard, Datura, Chilli. • Zygomorphic flower: A flower can be divided into two similar halves only in one particular vertical plane. E.g. pea, gulmohur, bean, cassia etc. • Asymmetric (irregular) flower: It cannot be divided into two similar halves by any vertical plane passing through the centre. E.g. canna.
