Understanding Xerophyte and Hydrophyte Adaptations

Xerophyte Adaptations

(Plants adapted to dry/arid environments – e.g., cactus, Opuntia)

1. Structural Adaptations

• Thick cuticle to reduce water loss.
• Sunken stomata to trap moisture and reduce transpiration.
• Reduced leaves (spines) to minimize water loss.
• Thick stems that store water (succulent stems).
• Deep or widespread roots to access water from deeper soil layers.

2. Physiological Adaptations

• CAM photosynthesis (in some) to open stomata at night.
• High osmotic pressure to absorb water quickly.
• Fewer stomata in number or present only on the lower surface.

Hydrophyte Adaptations

(Plants adapted to aquatic environments – e.g., lotus, water hyacinth)

1. Structural Adaptations

• Thin cuticle or absent cuticle as water is abundant.
• Large air spaces (aerenchyma) in stems and leaves for buoyancy.
• Stomata on the upper surface of floating leaves.
• Reduced or no xylem since water is absorbed directly.
• Highly dissected or ribbon-like leaves for movement in water.

2. Physiological Adaptations

• Less developed mechanical tissues (support is provided by water).
• Floating leaves with a broad surface area for maximum sunlight.

What are Ovules?

An ovule is the structure in seed plants that develops into a seed after fertilization. It is located inside the ovary of a flower and contains the female gametophyte (embryo sac), which produces the egg cell.

Structure of an Ovule

• Nucellus: Central tissue that nourishes the embryo sac.
• Embryo sac: Female gametophyte (contains egg cell).
• Integuments: Protective layers around the ovule.
• Micropyle: Small opening through which the pollen tube enters.
• Funicle: Stalk attaching the ovule to the ovary wall.
• Chalaza: Region opposite the micropyle.

Types of Ovules in Plants

1. Orthotropous Ovule

• Straight ovule.
• Micropyle, chalaza, and funicle are in one vertical line.
• No curvature.
• Example: Polygonum, Piper.

2. Anatropous Ovule

• Most common type in angiosperms.
• Ovule is completely inverted.
• Micropyle comes to lie close to the funicle.
• Example: Mustard, Sunflower.

3. Hemianatropous Ovule

• Ovule is partially turned.
• Body of the ovule is at a right angle (90°) to the funicle.
• Micropyle and chalaza are not aligned.
• Example: Primula.

4. Campylotropous Ovule

• Ovule is curved, embryo sac is also slightly curved.
• Micropyle and chalaza are not in one line.
• Example: Legumes, Chenopodium.

5. Amphitropous Ovule

• Ovule is curved like a horseshoe.
• Embryo sac is also curved.
• Example: Lemna, Poppy.

6. Circinotropous Ovule

• Ovule turns 360° during development.
• Funicle forms a coil around the ovule.
• Example: Opuntia (Cactus).