- Morphology is the study external structure of plant.
- This description is require in classification and evolutionary biology.
- Ukranian biologist Dr. Katharine Esau wrote two famous books -
“PLANT ANATOMY” (1954)
“THE ANATOMY OF SEED PLANT” (1960)
- referred to as Webster’s of plant biology
1. The Root
- Positive geotropic,
- Negative phototropic
2. Tap Root System
- Primary root with several orders of lateral roots (secondary, tertiary roots etc) makes the tap root system.
- Primary root is direct elongation of radicle.
- Tap root system is found in dicot plants e.g. mustard plant.
3. Fibrous root System
- It is originate from the base of stem.
- It is found in monocots e.g. Wheat etc.
- In monocot first root is primary root which is short lived and replaced by fibrous roots.
4. Adventitious Root
- Root which arise other than radicle.e.g. monstera, banyan and grass.
- 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 and synthesis of plant growth regulators.
5. Regions of The Root
- Root cap: Protection to Root meristem
- Region of meristematic activity: divide repeatedly.
- Region of elongation: undergo rapid elongation and enlargement and are responsible for the growth of the root in length.
- Regions of maturation: The cells of the elongation zone gradually differentiate and mature and make this zone. Epidermal cells of this zone form very fine and delicate, thread-like structures called ROOT HAIRS.
- These root hairs absorb water and minerals from the soil.
6. Modification of root
- Tap roots of carrot, turnip and adventitious roots of sweet potato & asparagus get swollen and store food.
- Prop roots of banyan tree for mechanical support.
- Stilt roots arise from stem in maize & sugarcane provide mechanical support. o Pneumatophores of Rhizophora (growing in swampy area) is negative geotropic root which help to get oxygen for respiration of main root.
7. The Stem
- Ascending part of the axis
- Bearing branches, leaves, flowers and fruits.
- It develops from the PLUMULE of the embryo of a germinating seed.
- THE STEM BEARS NODES AND INTERNODES.
- The region of the stem where leaves are born are called nodes while internodes are the portions between two nodes.
- The stem bears buds, which may be terminal or axillary.
- It conducts water, minerals and photosynthates.
- Some stems perform the function of storage of food, support, protection and of vegetative propagation
- Underground stems of potato, ginger, turmeric, zaminkand, Colocasia are MODIFIED TO STORE FOOD in them and also act as organ of perennation during unfavourable season.
- STEM TENDRILS which develop from axillary buds, are slender and spirally coiled and help plants to climb such as in gourds (cucumber, pumpkins, watermelon) and grapevines.
- Thorn of citrus and bougainvillea are axillary bud of stem and protect the plant from browsing animals.
- PHYLLOCLADE is the modified stem which perform photosynthesis e.g. opuntia and euphorbia.
- Underground stems of some plants such as grass(RUNNER) and strawberry(STOLON), etc., spread to new niches and when older parts die new plants are formed.
- Stolon is a slender lateral branch arises from the base of the main axis and after growing aerially for some time arch downwards to touch the ground.e.g. mint and jasmine.
- OFFSET a lateral branch with short internodes and each node bearing a rosette of leaves and a tuft of roots is found in aquatic plants like Pistia and Eichhornia.
- SUCKER→ In banana, pineapple and Chrysanthemum, the lateral branches originate from the basal and underground portion of the main stem, grow horizontally beneath the soil and then come out obliquely upward giving rise to leafy shoots.
8. Never Forget
- Potato: tuber.
- Ginger, turmeric: rhizome
- Zaminkand/suran/Amorphophallus: corm.
- Colacasia/kachalu: Corm.
- Opuntia(cactus), euphorbia: phylloclade.
- Cucumber, pumpkin, watermelon: stem tendril (modified axillary bud).
- Citrus, bougainvillea: Thorn (modified axillary bud).
- Grass: Runner.
- Strawberry: stolon.
- Pistia, Eichornia: Offset.
- Banana, Pineapple, chrysanthemum: Sucker.
9. The Leaf
- Lateral structure,
- born on node,
- bear a bud (axillary bud) in its axil,
- arise from shoot apical meristem arranged in acropetal order.
- Food factory of plant.
- A typical leaf consists of three main parts: leaf base, petiole and lamina.
- Leaf base is point of contact between stem and petiole.
- Leaf base may have two lateral small leaf like structures called STIPULES.
- In monocotyledons, the leaf base expands into a sheath covering the stem partially or wholly.
- Swollen leaf base is called PULVINUS is present in leguminous plant.
- Petiole function is, to hold the leaf blade in light for photosynthesis, keep the leaf cool by fluttering etc.
- Lamina /leaf blade is expanded green part of the leaf with veins and veinlets.
- Mid rib is the prominent mid vein.
- Veins provide rigidity to the leaf blade and act as channels of transport for water, minerals and food materials.
10. TYPES OF LEAVES
11. Simple Leaf
- Lamina is entire or if it is incised the incision does not touch the midrib.
12. 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.
13. AXILLARY BUD is present in axil of both simple and compound leaf but not in axil of leaflet.
14. IN A 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.
15. IN PALMATELY COMPOUND LEAVES, the leaflets are attached at a common point, i.e., at the tip of petiole, e.g. silk cotton.
- Phyllotaxy is the pattern of arrangement of leaves on the stem or branch.
- This is usually of three types – alternate, opposite and whorled.
- Alternate: leaf arises on alternate node.e.g. china rose, mustard and sun flower
- Opposite: A pair of leaves arises on each node.e.g. Calotropis and guava.
- Whorl: more than two leaves arise from each node. E.g. Alstonia.
17. Modifications of Leaves
- Leaf is modified into tendril in pea.
- Leaf is modified into spines for defence as in cacti.
- The fleshy leaves of onion and garlic store food.
- Phyllode is modified petiole perform the function of photosynthesis.
- Australian acacia, the petioles in these plants expand, become green and synthesise food.
- Leaves of certain insectivorous plants such as pitcher plant, Venus-fly trap are also modified leaves.
18. The Inflorescence
- The arrangement of flowers on the floral axis
- In Racemose type of inflorescences, the main axis continues to grow, the flowers are borne laterally in an acropetal succession.
- In cymose type of inflorescence the main axis terminates in a flower, hence is limited in growth. The flowers are borne in a basipetal order.
- a modified shoot o the shoot apical meristem changes to floral meristem.
- Internodes do not elongate and the axis gets condensed.
- When a shoot tip transforms into a flower, it is always solitary.
- The flower is the sexual reproductive unit in the angiosperms.
- Thalamus/receptacle is swollen end of pedicel(flower stalk) on which different whorl of floral appendages present.
- Floral appendages are
- CALYX, COROLLA, ANDROECIUM AND GYNOECIUM.
- The mode of arrangement of sepals or petals in floral bud in calyx or corolla
- VALVATE: when sepal/petal touch each other at the margin only.
- TWISTED: when margin of sepals/petals overlap each other.
E.g. china rose, lady’s finger and cotton.
- IMBRICATE: If the margins of sepals or petals overlap one another but not in any particular direction
in Cassia and gulmohur.
- VEXILLARY: In pea and bean flowers, there are five petals, the largest (standard) overlaps the two lateral petals (wings) which in turn overlap the two smallest anterior petals (keel); this type of aestivation is known as vexillary or papilionaceous.
21. When a flower has both androecium and gynoecium, it is BISEXUAL.
22. If either androecium or gynoecium is present then it is called UNISEXUAL FLOWER.
23. Calyx and corolla are accessory organs, while androecium and gynoecium are reproductive organs.
24. Only one accessory whorl is present instead of calyx and corolla. E.g. lily.
- Outermost accessory whorl,
- its single unit is called sepal which is green, leaf like and protect the flower in the bud stage.
- The calyx may be gamosepalous (sepals united) or polysepalous (sepals free).
- composed of petals.
- usually brightly coloured to attract insects for pollination.
- United petals: gamopetalous
- Independent petals: polypetalous.
- composed of stamens.
- Each stamen → male reproductive organ.
- A sterile stamen is called staminode.
- When stamens are attached
(i) Epipetalous When attached to the petals, as in brinjal.
(ii) Epiphyllous when attached to the perianth. E.g. lily.
- Polyandrous: If the stamens in a flower may remain free.
- Union of stamen( with stamens)
(i) Monoadelphous as in china rose.
(ii) Didelphous:as in pea.
(iii) Polyadelphous as in citrus.
- Salvinia & mustard show variation in the length of filaments within a flower.
- female reproductive part of the flower
- made up of one or more carpels.
- A carpel consists of three parts namely stigma, style and ovary.
- Ovary is the enlarged basal part.
- Each ovary bears one or more ovules
- Ovules attached to a flattened, cushion-like placenta.
- After fertilisation, the ovules develop into seeds o After fertilisation, the ovary matures into a fruit.
29. According to position of ovary in respect to other whorl of flower the flower may be
- Hypogynous: superior ovary
- in mustard, china rose, brinjal
- Epigynous: inferior ovary,
- Example guava and cucumber, and the ray florets of sunflower.
- Perigynous: Half inferior ovary,
e.g., plum, rose, peach.
30. Stigma is receptive surface for pollen grain.
if carpels are free to each other.e.g. lotus and rose.
carpels are fused with each other. Example mustard & tomato.
- The arrangement of ovules within the ovary.
- Types of placenta
(i) Marginal placentation. e.g. pea.
(ii) Axial: e.g. china rose, tomato, lemon.
(iii) Parietal: Ovary is one-chambered but it becomes two chambered due to the formation of the false septum, e.g., mustard and Argemone.
(iv) Free central: the ovules are borne on central axis and septa are absent, as in Dianthus and Primose.
(v) Basal placentation: the placenta develops at the base of ovary and a single ovule is attached to it, as in sunflower, marigold.
34. The Fruit
- Mature or ripened ovary, developed after fertilisation.
- If a fruit is formed without fertilisation of the ovary, → Parthenocarpic fruit.
- The fruit wall is called pericarp.
- The pericarp may be dry or fleshy.
- When pericarp is thick and fleshy, it is differentiated into the outer epicarp, the middle mesocarp and the inner endocarp.
- In mango and coconut, the fruit is known as a DRUPE. They develop from monocarpellary superior ovaries and are one seeded.
- In mango the pericarp is well differentiated into an outer thin epicarp, a middle fleshy edible mesocarp and an inner stony hard endocarp.
- In coconut which is also a drupe, the mesocarp is fibrous.
35. The Seed
- The ovules after fertilisation, develop into seeds.
- A seed is made up of a seed coat and an embryo.
- The embryo is made up of a radicle, an embryonal axis and one (as in wheat, maize) or two cotyledons (as in gram and pea).
- Testa and tegmen are seed coat.
-They are basically outer and inner integument of ovule.
- Hilum is the scar in seed
- show the point of attachment of seed with fruit.
- Micropyle is the small pore in seed which aloe the entry of water, oxygen. o In dicot, two cotyledons are present.
- The cotyledons are often fleshy and full of reserve food materials provide food to embryo during germination.
- Generally, monocotyledonous seeds are endospermic but some as in orchids are non-endospermic.
- The outer covering of endosperm separates the embryo by a proteinous layer called ALEURONE LAYER in monocot embryo.
- The embryo is small and situated in a groove at one end of the endosperm.
- It consists of one large and shield shaped cotyledon known as SCUTELLUM.
- The plumule and radicle are enclosed in sheaths which are called coleoptile and coleorhiza respectively.
36. Description of some important families
37. Family - FABACEAE
- Also called Papilionoidea, a subfamily of family Leguminosae.
- Floral Formula: % K(5) C1+2+(2) A(9)+1 G1
- Economic importance
(i) Sources of pulses → gram, arhar, sem, moong, soybean;
(ii) Sources of edible oil → soybean, groundnut;
(iii) Dye → Indigofera;
(iv) Plant fibres à sun hemp;
(v) Fodder → Sesbania, Trifolium,
(vi) Ornamentals → Lupin, sweet pea;
(vii) Medicine → muliathi
- Calyx show velvate/imbricate aestivation but petals(corolla) show vexillary aestivation.
- Root nodules are found in this family (symbiotic N2 fixation).
38. Family - Solanaceae
- It is a large family, commonly called as the ‘potato family’.
- Economic Importance
(i) Source of food → tomato, brinjal, potato,
(ii) Spice → chilli;
(iii) medicine → belladonna, ashwagandha;
(iv) fumigator → tobacco;
(v) Ornamentals → Petunia
39. Family - Liliaceae
- Commonly called the ‘Lily family’
- a characteristic representative of monocotyledonous plants.
- Vegetative characters:
- Perennial herbs with underground bulbs/corms/rhizomes.
- Floral Formula: Br ⊕ P (3+3) A3+3 G (3). (flower is bisexual)
- Economic Importance
(i) Ornamentals → tulip, Gloriosa,
(ii) Source of medicine → Aloe,
(iii) Vegetables → Asparagus, and
(iv) Colchicine → Colchicum autumnale
40. The floral characteristics form the basis of classification and identification of flowering plants.