"Reproduction in which new individuals are formed without fusion of gametes is called
asexual reproduction."
Apomixis is a form of asexual reproduction that mimics sexual reproduction.
Some species of Asteraceae and grasses have evolved a special mechanism, to produce
seeds without fertilization, called apomixis.
[In Greek - Apo = without; mixis = mixing] Apomixis term was suggested by Winkler.
The Apomixis is characterised by quick multiplication and production of genetically similar
plants from the single parent. The offsprings formed by asexual reproduction are identical
and are referred to as clones and each member of the clone is called ramet.
Agamospermy is included in apomixis.
AGAMOSPERMY :
In this type of method embryo is formed without fertilization and meiotic division. It
means plants belonging in this category propagate through seeds but the embryo
formation does not involve meiosis and syngamy.
It occurs by following three methods :-
(i) DIPLOSPORY :-
In this method megaspore mother cell directly gives rise to an embryosac without
meiosis. This embryo sac is diploid.
Example : Members of Asteraceae e.g. Parthenium
(ii) ADVENTIVE EMBRYONY :-
In this method, an embryo is formed from any diploid cell [Cell of nucellus or
integuments] of the ovule. This diploid cell behaves like a zygote. Adventive
embryony derived from Nucellus can be seen in Citrus, Mangifera (Mango),
Opuntia.
Sporophytic budding : In this process some of the nucellar cells surrounding the
embryosac start dividing, protrude into the embryosac and develop into embryos. It
is adventive embryony.
(iii) APOSPORY :-
Formation of gametophyte directly from sporophyte without meiosis is called
apospory.
In this method embryosac or female gametophyte is directly formed from any
diploid cell of the sporophyte i.e. nucellus or integument (except megaspore
mother cell) without meiosis. In this gametophyte always remains diploid, e.g.
Hieracium (member of Asteraceae).
