B. Angiospermae

(Angios : enclosed: vessel, Sperma : seed)

Angiosperms are the most advanced group of flowering plants.

In these plants the seeds are enclosed within the fruit i.e. ovary.

Angiosperms is a group of highly evolved plants, primarily adapted to terrestrial habitat. They vary in size.

Angiosperms show heteromorphic alternation of generation in which the sporophyte is diploid, dominant, autotrophic and independent.

The gametophytes (male or female) are recessive, haploid and dependent on the sporophyte.

Angiosperms heterosporous. Microspores (commonly called pollens) are formed in microsporangia (or anthers).

They develop in highly specialized microsporophyll or stamens while megaspores are formed in megasporangia (or ovules) borne on highly specialized megasporophyll called carpel.

Besides the essential whorls of microsporophylls (Androecium) and megasporophylls (Gynoecium) there are accessory whorls namely calyx (sepals) and corolla (petals) arranged together to form flowers.

Wolffia is the smallest Angiosperm, 1mm in size and Eucalyptus grows to over 100 meters.

 

Angiosperms are subdivided into two classes:

a. Dicotyledonae :

These plants have two cotyledons in their embryo.

They have a tap root system and the stem is branched.

Leaves show reticulate venation while the flowers show tetra or pentamerous symmetry.

Vascular bundles are conjoint,collateral and open type.

Cambium is present between Xylem and Phloem for secondary growth.

In Dicots secondary growth is commonly found,

e.g. Helianthus annus (sunflower), Hibiscus rosa-sinensis (China rose).

 

a. Monocotyledonae :

These plants have single cotyledon in their embryo.

They have adventitious root system and stem is rarely branched.

Leaves generally have sheathing leaf base and parallel venation while the flowers are generally trimerous.

The vascular bundles are conjoint, collateral and closed type.

In Monocots, except few plants secondary growth is absent.

e.g. Zea mays (Maize), Sorghum vulgare (Jowar).

 

1. What are the salient features of Angiosperms?

2. What is double fertilization ?

3. Explain in brief two classes of Angiosperms? Draw and label one example of each class.

4. Give general characters of Gymnosperms and Angiosperms.

5. Distinguish between Dicotyledonae and Monocotyledonae.

6. Why do Dicots show secondary growth while Monocots don't?