ANGIOSPERMS
- Angiosperms are seed plants in which seeds are formed inside fruits and the sporophylls are organised into flowers.
- Angiosperms are the most recently and highly evolved plants.
- Angiosperms are found in most environments on the earth.
- Plant body is sporophytic and represented by herbs, shrubs, trees, twiners, trailers, climbers, etc.
- Sporophytic plant body is differentiated into roots, stem and leaves.
- Depending upon the number of cotyledons (embryonic leaves) in the seeds, angiosperms are divided into two subgroups :
dicotyledonous and monocotyledonous plants. - Xylem contains vessels and phloem possesses sieve tubes and companion cells.
- Secondary growth occurs in root and stem of dicots.
- Sporophylls are aggregated to form flowers. Both microsporophylls and megasporophylls are specialised to form stamen and
carpel producing male and female gametes respectively. - Female gametophyte is represented by embryo sac. All the cells of embryo sac are haploid.
- Pollination takes place by several agencies such as air, water, birds, insects, bats, etc.
- The flowers possess showy petals, edible pollen and nectar to attract various pollinating agents.
- Pollen grains or microspores reach stigmatic surface found at the tip of carpel or megasporophyll.
- Embryo sac develops upto 8-nucleate state before fertilisation. There is a three cell egg apparatus, three antipodal cells and two polar
nuclei. - Double fertilisation is characteristic feature of angiosperms. One
of the two male gametes, fuses with egg to form zygote while
other fuses with central cell to form primary endosperm nucleus
(PEN). - Central cell containing triploid primary endosperm nucleus
forms triploid endosperm. Endosperm provides nourishment
to developing embryo. - Synergids and antipodals degenerate after fertilisation.
- Fertilised ovules ripen into seeds. The seeds are covered by
fruits. - A fruit is a ripened ovary which not only protects the seeds but
also help in their dispersal.