MORPHOLOGY OF FLOWERING PLANTS :
THEORETICAL PART 2 :
4 STEM :
4.1 General Information
- It develops from the plumule of the embryo of a germinating seed.
- The stem bears nodes and internodes.
- The main function of the stem is spreading out branches bearing leaves, flowers and fruits.
4.2 Modified Sub-Aerial Stems: RUNNER
- When stem grows and spread on the surface of soil. Roots are developed at lower side and leaves from upper side from node.
- E.g. Cynodon dactylon (Doob grass), Oxalis
4.3 Modified Sub-Aerial Stems: STOLON
- Elongated, horizontal lateral branch developing from the lower part of the man axis for some distance like an arch and then touching the ground to give rise to new shoot.Class 11, Class 11biology notes, Class 11 Biology, Class 11 Biology chapter 1 , Class 11 Biology chapter 2, Class 11 Biology morphology of flowering plants
- E.g. Fragaria (Wild strawberry), Jasminum, Peppermin
4.4 Modified Sub-Aerial Stems: OFFSET
- Short, only one internode long and thicker small runners bearing a cluster of leaves in rossette manner
- Adventitious roots arising from all nodes
- E.g. Pistia, Eichhornia
MORPHOLOGY OF FLOWERING PLANTS :
4.5 Modified Underground Stems: Sucker
- Non-green underground stem developing from an erect shoot
- Grows horizontally in the soil and then comes out to form a new shoot
- Shorter and stouter than an underground runner
- E.g. garden mint, Chrysanthemum
4.6 Modified Underground Stems: Rhizome
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- Rhizome is a modified underground stem.
- Stem is divided into nodes and internodes. Adventitious root on lower node.
- Example Ginger, Turmeric, Canna
MORPHOLOGY OF FLOWERING PLANTS :
4.7 Modified Underground Stems: Corm
- Short, thick, highly condensed, swollen, usually unbranched, spherical or sub spherical underground stem
- Produced annually and grows vertically in the soil
- E.g. Amorphophallus, Crocus, Colocasia
4.8 Modified Underground Stems: Bulb
- It is an underground pyriform-spherical structure that possesses a reduced convex or slightly conical disc-shaped stem.
- It stores food in scales, leaf base and bud.
- Example: Onion
4.9 Modified Underground Stems: Tuber
- Swollen underground stem developing at the growing tip of a branch (sucker or stolon) •
- Oval or spherical lacking adventitious roots and possessing a number of spirally arranged depressions called eyes
- E.g. Amorphophallus, Crocus, Colocasia
- 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
4.11 Modified Weak Aerial Stem: Thorns
- Axillary buds of stems may also get modified into woody, straight and pointed thorns.
- Thorns are found in many plants such as Citrus, Bougainvillea.
- They protect plants from browsing animal
4.12 Modified Erect Aerial Stems: Phylloclade
- Stem is modified into a flat, fleshy and green leaf like structure and carries out photosynthesis like leaf. •
- The leaves are modified into spines
- E.g. Opuntia, Euphorbia, Casuarina
4.13 Modified Erect Aerial Stems: Cladodes
- Typical phylloclade only one internode long
- Stem branches of limited growth and green
- True leaves reduced to scales or spines
- E.g. Ruscus, Asparagus
5. THE LEAF :
Leaf is a green, dissimilar exogenous lateral flattened outgrowth which is borne
on the node of a stem or its branches is specialized to perform photosynthesis.
5.1 Types of Venations
- Reticulate- present in dicotyledons, there is a network of vein present, which are irregularly distributed.
- Parallel- present in monocotyledons, veins are parallel to each other.
5.2 Types of Leaves
- Simple- lamina is complete and incision doesn’t reach midrib
- Compound- incision touches midrib, that divides a leaf into a number of leaflets. Pinnately compound- the leaflets are present on common axis, i.e. midrib called the rachis
- Example: Neem.
- Palmately compound- leaflets are attached at the petiole tip, e.g. silk cotton
5.3 Phyllotaxy
- Pattern of arrangement of leaves around the stem
- Alternate type- single leaf present at each node, e.g. Hibiscus, Brassica.
- Opposite type- each node bears a pair of leaves, e.g. Psidium guajava, Calotropis.
- Whorled type- more than two leaves arise at the node to form a whorl, e.g. Alstonia.
5.4 Modifications of leaves
- Tendrils: a leaf modified to form long thread-like structure, it gives support to climbers, e.g. peas.
- Spine: In xerophytic plants to reduce water loss, e.g. cactus, aloe.
- For storage: e.g. garlic, onion.
- Phyllodes: petiole gets modified to form a leaf-like structure and function,
- e.g. Acacia.
- Pitcher in pitcher plant is a modified leaf which traps insect inside.
Class 11, Class 11biology notes, Class 11 Biology, Class 11 Biology chapter 1 , Class 11 Biology chapter 2, Class 11 B
iology morphology of flowering plants
