Vegetative Propagation and Seeds
Introduction
Plants can reproduce both sexually (through seeds) and asexually (through vegetative propagation). ICSE Class 9 covers artificial propagation methods, seed structure, and germination.
Natural Vegetative Propagation
Plants naturally produce new individuals from vegetative parts (roots, stems, leaves).
| Plant Part | Method | Examples |
|---|---|---|
| Root | Adventitious buds develop into new plants | Sweet potato, Dahlia |
| Stem (underground) | Tubers, rhizomes, bulbs, corms | Potato (tuber), Ginger (rhizome), Onion (bulb) |
| Stem (above ground) | Runners, stolons, suckers | Strawberry (runner), Mint (sucker) |
| Leaves | Leaf margins develop plantlets | Bryophyllum |
Artificial Vegetative Propagation
Cutting
A portion of stem or root is cut and planted to grow into a new plant. Examples: Rose, sugarcane, hibiscus
Layering
A branch is bent down, covered with soil while still attached to the parent. Roots develop, and the branch is later separated. Examples: Jasmine, bougainvillea
Grafting
The stem of one plant (scion) is joined to the root system of another (stock).
- Scion: Upper part with desired fruits/flowers
- Stock: Lower part with strong roots
- Examples: Mango, apple, rose
| Method | Advantages | Disadvantages |
|---|---|---|
| Cutting | Simple, fast | Not all plants root easily |
| Layering | Higher success rate | More time-consuming |
| Grafting | Combines best traits of two plants | Requires skill; limited to related species |
Monocot and Dicot Seeds
Monocot Seed (e.g., Maize)
- Single cotyledon (scutellum)
- Endosperm present (albuminous seed)
- Seed coat fused with fruit wall
- Example: Maize, wheat, rice
Dicot Seed (e.g., Bean, Gram)
- Two cotyledons
- Endosperm may be absent (exalbuminous) or present
- Seed coat: Testa (outer) + Tegmen (inner)
- Micropyle: Small opening for water entry
- Hilum: Scar where seed was attached to ovary wall
- Embryo: Plumule (shoot), Radicle (root), Cotyledons (seed leaves)
| Feature | Monocot Seed | Dicot Seed |
|---|---|---|
| Cotyledons | 1 | 2 |
| Endosperm | Present | Often absent |
| Examples | Maize, rice, wheat | Bean, pea, gram |
| Germination | Hypogeal usually | Epigeal usually |
Seed Germination
Conditions Required for Germination
- Water: Activates enzymes; softens seed coat
- Oxygen: Required for respiration (energy for growth)
- Suitable temperature: Enzymes work best at optimal temperature
- Light: Required by some seeds (photoblastic)
Types of Germination
Epigeal Germination
- Cotyledons come above the soil
- Hypocotyl elongates (region below cotyledons)
- Examples: Bean, castor, sunflower
Hypogeal Germination
- Cotyledons remain underground
- Epicotyl elongates (region above cotyledons)
- Examples: Pea, maize, wheat
| Feature | Epigeal | Hypogeal |
|---|---|---|
| Cotyledon position | Above ground | Below ground |
| Elongating part | Hypocotyl | Epicotyl |
| Examples | Bean, castor | Pea, maize |
Common Mistakes With Fixes
| Mistake | Correction |
|---|---|
| Potato is a root for propagation | Potato is a modified STEM (tuber), not a root |
| All seeds need light for germination | Some seeds germinate in darkness |
| Monocots have two cotyledons | Monocots have ONE cotyledon; dicots have TWO |
| Grafting works between any two plants | Grafting requires plants to be closely related |
ICSE Exam Focus
| Topic | Marks (approx.) | Frequency |
|---|---|---|
| Artificial propagation (cutting, layering, grafting) | 4-5 marks | Very common |
| Monocot vs dicot seeds | 3-4 marks | Common |
| Epigeal vs hypogeal germination | 3-4 marks | Common |
| Conditions for germination | 3 marks | Frequently asked |
Self-Test
Q1: Distinguish between monocot and dicot seeds (3 points).
Q2: Explain any two methods of artificial vegetative propagation.
Q3: What conditions are necessary for seed germination?
Q4: Differentiate between epigeal and hypogeal germination with examples.
Q5: Why is grafting not possible between all plants?
