Morphology of Flowering Plants :Modification of Stem & Leaf | Lec. 10 | NCERT | Indush Study Circle

Morphology of Flowering Plants: Modification of Stem and Leaves
By N. P. Narain Sir – Indush Study Circle

Introduction
In flowering plants, different parts undergo modifications to adapt to environmental conditions, aid in survival, and perform specialized functions. The stem and leaves, which primarily support the plant and perform photosynthesis, often transform to perform additional roles such as storage, protection, vegetative propagation, and climbing. This chapter explores various modifications of the stem and leaves.

Modification of Stem
The stem typically provides support, transports nutrients, and bears leaves, flowers, and fruits. However, it often modifies itself to store food, survive harsh conditions, or assist in propagation. These modifications can be categorized into underground, subaerial, and aerial modifications.

1. Underground Stem Modifications
Underground stems store food, perennate under unfavorable conditions, and facilitate vegetative propagation. Though they resemble roots, they possess nodes, internodes, scale leaves, and buds.

a) Rhizome
A thick, horizontal underground stem with distinct nodes and internodes.

Helps in vegetative propagation.

Example: Ginger (Zingiber officinale), Turmeric (Curcuma longa).

b) Tuber
A swollen, underground stem storing starch.

Bears "eyes" (axillary buds) that sprout into new plants.

Example: Potato (Solanum tuberosum).
d) Corm
A thick, upright underground stem with nodes and internodes.

Bears buds that develop into new shoots.

Example: Colocasia (Colocasia esculenta), Gladiolus (Gladiolus spp.).

2. Subaerial Stem Modifications
These modifications occur at or just below the surface and help in vegetative propagation.

a) Runner
A horizontal stem that spreads along the soil surface, producing new plants at nodes.

Example: Grass (Cynodon dactylon), Strawberry (Fragaria vesca).

b) Stolon
A lateral stem that bends down and forms roots at the tip, producing a new plant.

Example: Mint (Mentha), Jasmine (Jasminum).

d) Sucker
An underground stem that grows obliquely and emerges above ground as a new shoot.

Example: Banana (Musa), Chrysanthemum (Chrysanthemum indicum).

3. Aerial Stem Modifications
In some plants, the stem undergoes modifications to support, protect, or aid in survival.

a) Stem Tendrils
Slender, coiled structures arising from axillary buds that help plants climb.

Example: Cucumber (Cucumis sativus), Grape Vine (Vitis vinifera).

b) Thorns
Hard, pointed structures that protect plants from herbivores.

Example: Bougainvillea (Bougainvillea), Citrus (Citrus limon).

c) Phylloclade
A flattened or cylindrical green stem that performs photosynthesis in xerophytic plants.

Example: Opuntia (Opuntia spp.), Euphorbia (Euphorbia spp.).

d) Cladode
A short-lived, photosynthetic stem modification.

Example: Asparagus (Asparagus officinalis), Ruscus (Ruscus aculeatus).

e) Bulbil
A small, fleshy bud that detaches and grows into a new plant.

Example: Agave (Agave americana), Dioscorea (Dioscorea bulbifera).

Modification of Leaves
Leaves primarily function in photosynthesis and transpiration. However, in some plants, they modify into tendrils, spines, or traps to serve specialized functions.

1. Leaf Tendrils
Slender, coiled structures that help climbing plants attach to a support.

Example: Pea (Pisum sativum), Sweet pea (Lathyrus odoratus).

2. Leaf Spines
Hard, pointed structures that protect plants from herbivores and reduce water loss.

Example: Cactus (Opuntia), Aloe (Aloe vera).

3. Leaf Scale
Dry, membranous structures found in underground stems to protect buds.

Example: Onion (Allium cepa), Garlic (Allium sativum).

4. Phyllode
A modified petiole that performs photosynthesis, replacing the leaf blade in arid plants.

Example: Australian Acacia (Acacia auriculiformis).

Conclusion
The modifications of the stem and leaves demonstrate how plants adapt to their environment for survival, storage, protection, and propagation. These changes ensure their ability to thrive in diverse habitats.

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