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PinkMonkey Online Study Guide-Biology

15.3 Angiosperms : Dicotyledons

Angiosperms are the flowering plants in which the seed is enclosed and protected in the pericarp  (i.e. the fruit wall). Angiosperms represent the highest evolved and most specialized group in the kingdom Plantae. These are also the most thriving and seen almost all over the world.

(A) Distinguishing characters of Angiosperms

  • The plant body is more complex and better adapted than other plant groups.

  • Vascular tissues have specialized conducting elements (e.g., vessels in xylem and sieve tubes and companion cells in phloem).

  • The plant body is a diploid sporophyte differentiated into roots, stem and leaves.

  • There is the development of a flower as a highly specialized reproductive organ.

  • The carpels in the gynoecium have ovary, style and stigma.

  • Ovules are enclosed inside an ovary cavity.

  • Heterosporous condition.

  • Highest reduction in male and female gametophytes.

  • Archegonia totally absent in female gametophyte.

  • Male gametes are non-motile.

  • Pollen grains are deposited on the stigma of the gynoecium during pollination (and not directly in the pollen chamber inside the ovule as in gymnosperms).

  • Phenomenon of double fertilization is the characteristic of angiosperms only.

  • Endosperm is triploid in nature and develops only after double fertilization is over (post-fertilization tissue).

  • Seeds are enclosed inside the pericarp (fruit wall) and thus, the embryo in the seed is very well protected and properly nourished.


Angiosperms are classified as dicotyledonous or monocotyledonous mainly on the basis of following criteria:

 

Criteria

Dicotyledonous

Monocotyledonous

(1)

Roots

Tap root system

Adventitious root system

(2)

Venation in leaves

Reticulate

Parallel

(3)

Symmetry of flower

Pentamerous or tetramerous

Trimerous

(4)

Number of Cotyledons in the embryo.

Two

One

Some common examples

Hibiscus (Chinarose), sunflower, mango, pea, bean.

corn, wheat, rice, grasses, onion, Asparagus, Canna, palms, coconut.

Table of Contents

15.0 - Introduction
15.1 Pteridophyta : General Account
15.2 Gymnosperms
15.3 Angiosperms : Dicotyledons
15.4 Angiosperms : Monocotyledons
15.5 Vascularization
15.6 Development of seed habit
15.7 Development of Flower and Fruit

Chapter 16





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