1) The ovary contains a cavity lined with epidermal cells. Ovules develop from these epidermal cells and are contained within the ovary cavity, attached by a stalk called the funiculus. 2) The ovule has four main parts: the nucellus at the center containing sporogenous cells, one or two integuments surrounding the nucellus, the funiculus stalk connecting the ovule to the placenta, and the chalaza where the nucellus, integuments and funiculus merge. 3) A megaspore mother cell within the nucellus undergoes meiosis to form a megaspore, which

1. X-section of an ovary Ovary contains a cavity
lined with an epidermal
layer. Ovules develop
from the epidermal
cells and are contained
within the cavity of the
ovary, attached to its
inner surface by a
short stalk- funiculus
Ovary bears
ovules on a
ridge on the
ovary wall
called placenta

3. Parts of ovule
1. nucellus- central body with vegetative cells enclosing the
sporogenous cells
2. 1 or 2 integuments (unitegmic or bitegmic) enclosing the
Nucellus
3. funuculus-stalk connecting ovule with the placenta.
4. chalaza-where nucellus, integuments and the funiculus
merge

4. Megaspore mother cell dev. from surrounding nucellar
tissue and undergoes meiotic division to form megaspore.
Nucellus considered as a megasporangium
Funiculus
nucellus
Chalaza- region where integuments fuse with funiculus

5. Development of embryo sac and female
gamete (in an anatropous ovule)
•A hypodermal cell of the nucellus enlarges and
becomes differentiated into a megaspore mother cell
or megasporocyte.
•This diploid megaspore mother cell increases in size
and undergoes meiosis to form a linear tetrad of 4
haploid megaspores,
•3 of which degenerate and the 4th becomes the
functional megaspore in monosporic types,
•all 4 become functional in tetrasporic types

6. Female Gametophyte
• The nucleus of the megaspore
undergoes three successive mitotic
divisions forming eight nuclei.
•The megaspore enlarges into an oval
shaped structure called the embryo
sac. The eight nuclei of the embryo sac
arrange themselves in 3 groups.

7. Darkly stained
cluster of cells
is the nucellus

9. Inner and outer
integuments
begin as ridges of
tissue

10. Inner integument
Outer integument
Differential
growth
causes
them to
curve
so
micropyle
is bent
around
funiculus

11. micropyle
funiculus

12. funiculus
placenta
Outer and inner
integuments completely
overgrow the nucellus

13. Megaspore mother cell dev. from surrounding nucellar
tissue and undergoes meiotic division to form megaspore.
Nucellus considered as a megasporangium
Funiculus
nucellus
Chalaza- region where integuments fuse with funiculus
Outer and inner
integuments
completely
overgrow the
nucellus

16. Developing ovules of Lilium. Ovule emerges from the
placenta as conical protuberance with the first
sporogenous cell,called archesporial cell.
Integuments formed by periclinal div. of epidermis

19. Or megaspore mother cell

20. Micropyle
Inner integument
Outer integument
placenta
funiculus
Outer and inner integument completely overgrow the nucellus
Except for the micropyle. (nucellus=central portion of ovule
inside the integuments )
--Begins with elongation of the functional megaspore,
usually at chalazal end.
-- initially megaspore is non-vacuolate but later small
vacuoles appear which may fuse to form large vacuole.
Development of
embryo sac

21. Embryo sac After 3 mitotic
divisions
Egg and synergids

24. Sporogenous cell develops directly from hypodermal
nucellar cell- large dense cytoplasm, large nucleus.
In others, hypodermal cell divides into outer parietal and inner
primary sporogenous cell.
meiosis
Hypodermal
archesporial
cell

25. meiosis

26. meiosis

27. Chalazal
region
Post meiosis: surviving
Megaspore will divide by
mitosis

29. A, D. (bel mutant)
exposed nucellus
and a single
integument
F. Larger mutant ovule
Outer integument has
many cells.

30. A. First megaspore mitosis yields binucleate embryo sac.
Spindle of first nuclear div oriented along the long axis of
the cell. Wall formation Does Not follow the nuclear
division. Both nuclei divide 2x, forming 4 in B then 8 in C
B. Large vacuole appears between the two daughter nuclei.
As cell expands, nuclei are pushed toward opposite poles
of the cell. Both nuclei from each pole divide twice

31. D. The 8 nuclei arrange themselves in two clusters of 4 nuclei
one at each opposite ends. One nucleus from each end
migrates towards the middle, called polar nuclei (named for
where they came from, not where they end up).
C.8-nucleate state . All
8 nuclei are present in
a common cytoplasm,
they move around
probably from
remnants of spindle
fibers from earlier
divisions.

32. Chalazal trio called antipodals
( Latin “against the foot”) at
opposite end of the egg and
antipodals
Egg apparatus consists of larger
egg flanked by two smaller cells
called synergids (greek for
“helpers” or cooperators
The large binucleate
Chalazal=basal part of ovule
where integument and nucellus
are joined

36. megasporogenesis
Megagameto-
genesis

37. Mutants in ovule determination
1. bell (bel1)- ovule lacks inner integument
2. Aberrant testa shape (ats)- no clear distinction between
inner and outer integument
3. Extreme types of integument mutations:
aintegumenta (ant)
huellenhos (hll)
Do not develop integument and
embryo is disrupted.

41. highly vacuolated
amount of cytoplasm is
limited cytoplasm spread as
a thin layer surrounding
vacuole
 cytoplasm contains very
little ER, limited no. of
plastids, mitochondria and
dictyosomes but high
ribosomes which are
randomly distributed rather
than aggregated as
polyribosomes
 cell wall does not extend
over the entire cell
EGG

43. Synergids- limited life span, wilt
after fertilization.
 Probably involved in
nutrition of egg. has extensive
wall ingrowth at micropylar
region called filiform apparatus
metabolically active
Antipodals-transient existence ,
minimal cytoplasmic organelle,
show nuclear abnormalities like
endoreplicationpolar nuclei-metabolically active,
extensive ER, numerous plastids,
mitochondria, dictyosomes and
polysomes, has large quantities of
starch, proteins and lipids

44. Megasporogenesis and microsporogenesis
megasporocyte microsporocyte
Generates megaspore and microspores
meiosis