1. Double fertilization and Triple
Fusion
Dr. Vasanta I. Kahalkar
Dept. of Botany
M. G. College, Armori
2. • Entry of Pollen Tube into the Ovule:
• After reaching the ovary, the pollen tube enters the
ovule through micropylar end. It then enters one of the
synergids through the filiform apparatus present at
micropylar end. The synergids direct the growth of
pollen tube by secreting some chemical substances.
• The tip of the pollen tube enters one synergid, then the
penetrated synergid starts degenerating. After
penetration, the tip of the pollen tube enlarges and
ruptures by releasing the contents, including the two
male gametes and vegetative nucleus.
4. • Entry of Pollen Tube into the Ovule:
After reaching the ovary, the pollen tube
enters the ovule. Pollen tube may enter the ovule
by one of the folowing routes:-
• Porogamy :- When the pollen tube enters the
ovule through micropylar end, it is called
porogamy. Eg.- Lily
• Chalazogamy : The entry pollen tube into the
ovule from chalazal region is known as
chalazogamy. Eg- Betula
• Mesogamy :- The pollen tube enter the ovule
through its middle part i.e. Integuments or
through funicle.
5. Double fertilization and Triple Fusion
• The process of fusion of one male gamete with the egg
along with the union of the second male gamete with the
two polar nuclei or the secondary nucleus is called double
fertilisation.
• Out of the two male gametes, one fuses with the egg to
carry out generative fertilization or syngamy. It gives rise to
a diploid zygote or oosphere.
• The nucleus of the second male gamete fuses with two
haploid polar nuclei or diploid secondary nucleus of the
central cell to form a triploid primary endosperm nucleus
(PEN). The central cell is called primary endosperm cell
(PEC). This is called vegetative fertilization or triple fusion
7. Significance of Double Fertilization
• Fusion of male and female gamete are store
diploid condition.
• There are chances of polyembryony, and the
plant has better chances of survival.
• Double fertilization gives rise to an endosperm
that provides nourishment to the developing
embryo.
• It increases the viability of the seeds of
angiosperms.
8. ENDOSPERM AND ITS TYPES
• Endosperm is the nutritive tissue for the
developing embryo and also the seedling. In
angiosperm the endosperm develops from
triploid (3n) primary endosperm nucleus which
is formed as a result of vegetative fertilization,
triple fusion or fusion of a male gamete with
secondary nucleus of the central cell.
9. Type of endosperm: on the basis of development endosperm
are three types:-
• Nuclear endosperm:- In the nuclear types of endosperm development
the primary endosperm nucleus divides by repeated mitotic free nuclear
divisions without the formation of walls. It result in the formation of a
large number of free nuclei in the central cell of the embryo sac. A big
central vacuole develops in the embryo sac pushing all the nuclei to the
peripheral cytoplasm. Finally cell wall formation takes place from the
periphery of the embryo sac towards the centre leading to the formation
of cellular endosperm tissue. In the Coconut, the endosperm is
multicellular in the outer part and free nuclear in the centre. Nuclear
endosperm is the most common type of endosperm and mostly found in
polypetalae. Eg.- Cotton.
10. CELLULAR ENDOSPERM
• In the cellular type of endosperm development the 1st nuclear
division of the endosperm nucleus is immediately followed by
wall formation. The 1st division result in the formation of two
equal sized chamber, chalazal and micropylar chambers. The
subsequent division are fallowed by regular cell wall
formation. This types of endosperm formation is common in
gamopetalae. Eg.-Datura.
11. Helobial endosperm
• In the Helobial type of endosperm development, the endosperm is
intermediate between cellular and nuclear types. The division of primary
endosperm nucleus is followed by wall formation and as a result two
chamber micropylar and chalazal chamber, are formed. Generally the
chalazal cell divides by repeated free nuclear divisions and further
development takes places in the same way as the nuclear endosperm.
Helobial type of endosperm development is prevent in Helobiales order of
monocotyledonds. Eg- Erumirus.
