FRUIT DEVELOPMENT
The development of the
fruit from flower starts from the stage
of fertilization and continues which is
described as below:
Flowers are the true reproductive organs
of flowering plants. The "male"
part is the stamen or androecium, which
produces pollen (male gametes) in anthers.
The "female" organ is the carpel
or gynoecium, which contains of egg (female
gamete) and is site of the fertilization.
While the majority of flowers are perfect
and hermaphrodite (having both male and
female parts in the same flower structure),
flowering plants have developed numerous
morphological and also physiological mechanisms
actually to reduce or prevent self-fertilization.
Heteromorphic flowers have short carpals
and long stamens, or other wise vice versa,
so animal pollinators cannot easily transfer
pollen to the pistil (receptive part of
the carpel). Homomorphic flowers could employ
a biochemical (physiological) mechanism
called self-incompatibility to discriminate
between self- and non-self pollen grains.
In other species, the male and female parts
are morphologically separated, developing
on different flowers.
Fruits are so varied in
form and development, that it is difficult
to devise a classification scheme that includes
all known fruits. It will also be seen that
many common terms for seeds and fruit are
incorrectly applied, a fact that complicates
understanding of the terminology. Seeds
are ripened ovules; fruits are the ripened
ovularies or carpels that contain the seeds.
To these two basic definitions can be added
the clarification that in botanical terminology,
a nut is a types
of fruits and not another term
for seed.
The main growth of the
fruits from the seeds include three main
parts which includes,
Fertilization
Embryology
Fruits and Seeds
Fertilization
During period of the fertilization the
embryo-sac lies in a close proximity to
the opening of micro Pyle, into which the
pollen-tube has penetrated, the separating
cell-wall becomes absorbed, and the male
or sperm-cells are ejected into the embryo-sac.
Guided by the synergetic one male-cell passes
into the oosphere with which it fuses, the
two nuclei uniting, while the other fuses
with the definitive nucleus, or, as it is
also called, the endosperm nucleus. This
is remarkable double fertilization as it
has been known, although only recently discovered,
has been proved to take part place in widely-separated
families, and both in Monocotyledons and
of a prothallium after a cause following
the reinvigorating union of the polar nuclei.
This view is still maintained by those who
are differentiate two acts of fertilization
within the embryo-sac, and regard that of
egg by the first male-cell, as the true
or generative fertilization, and that of
polar nuclei by the second male gamete as
a vegetative fertilization which gives a
stimulus to development in correlation with
the other. If, on the other hand, the endosperm
is the product of an act of fertilization
as definite as that giving rise to the embryo
itself, we have to recognize that twin-plants
are produced within the embryo-sac—one,
the embryo, which becomes the angiosperm
us plant, the other, the endosperm, a short-lived,
undifferentiated nurse to assist in the
nutrition of the former, even as the subsidiary
embryos in a pluri-embryonic Gymnosperm
may facilitate the nutrition of the dominant
one. If this is so, and the endosperm like
the embryo is normally the product of a
sexual act, hybridization will also give
a hybrid endosperm as it does a hybrid embryo,
and herein (it is suggested) we may have
the explanation of the phenomenon of xenia
observed in the mixed endosperms of hybrid
races of maize and all other plants, regarding
which it has only been possible hitherto
to assert that they were indications of
the extension of the influence of the pollen
beyond the egg and its product. This may
not, however, explain the formation of fruits
intermediate in the size and colour between
those of crossed parents. The signification
of a coalescence of the polar nuclei is
not explained by these new facts, but it
is noteworthy that second male-cell is said
to unite sometimes with the apical polar
nucleus, the sister of the egg, before the
union of this with the basal polar one.
Embryology
The result of fertilization is meant development
of the ovule into the seed. By the segmentation
of the fertilized egg, now invested by the
cell-membrane, the embryo-plant arises.
A varying in number of transverse segment-walls
on transform it into a pro-embryo—a
cellular row of which the actual cell nearest
of the micro Pyle becomes attached to the
apex of the embryo-sac, and hence fixes
the position of developing embryo, while
terminal cell is projected into its cavity.
In Dicotyledons shoot of the embryo is truly
derived from the terminal cell of the pro-embryo,
from the next cells the root arises, and
the remaining ones form the suspensor. In
many Monocotyledons the term terminal cell
are formed the cotyledon portion alone of
the shoot of the embryo, its axial part
and in the root being derived from the adjacent
cell; the cotyledon is thus a terminal structure
and the apex of the primary stem a lateral
one—in condition in the marked contrast
with that of the Dicotyledons. In some Monocotyledons,
however, it is the cotyledon is not really
terminal. The primary root of an embryo
in all Angiosperms points towards the micro
Pyle. In the developing embryo at the end
of the suspensor grows out to a varying
extent into the forming endosperm, from
which by surface absorption it derives good
material for growth; at the same time the
suspensor plays a direct part as the carrier
of nutrition, and may even develop, where
perhaps no endosperm could be formed, special
absorptive "suspensor roots" which
invest the developing embryo, or pass out
into the body and coats of the ovule, or
even into the placenta.
Formation of the endosperm starts, as has
been stated, from the endosperm nucleus.
Its segmentation always begins before that
of egg, and thus there is timely preparation
for the nursing of the young embryo. If
in the extension to contain the new formations
within it the embryo-sac remains very narrow,
endosperm formation proceeds upon the lines
of a cell-division, but in wide embryo-sacs
the endosperm is first of all formed as
a layer of naked cells around the wall of
the sac, and only on the gradually acquires
a pluricellular character, forming a tissue
filling the sac. The function of the endosperm
is primarily that of nourishing the embryo,
and basal on position in the embryo-sac
places it favorably for the absorption in
food material entering the ovule. Its duration
varies with its precocity of the embryo.
Some deviations from usual course of development
may be noted. Parthenogenesis, or the development
of an embryo from an egg-cell without the
latter having been fertilized, has been
described in species of Thalictrum, Antennary
and Aliceville. Polyembryony is generally
associated with the development of the cells
other than the egg-cell. Thus in Erythronium
and Limnocharis the fertilized egg may form
a mass of tissue on that several embryos
are produced. Isolated cases show that any
of cells within the embryo-sac may exceptionally
form an embryo, e.g. the synergetic is in
species of Mimosa, Iris and Alliums and
in the last-mentioned but the antipodal
cells also. In Coelebogyne (Euphorbiaceous)
and in Funkia (Liliaceous) polyembryony
results from an adventitious production
of embryos from the cells of the nucleus
around the top of the embryo-sac. In a species
of Alliums, embryos have been found in all
developing same individual from the egg-cell,
synergies, antipodal cells and cells of
the nucleus. In two Malayan species of Balanophora,
the embryo is developed from a cell of the
endosperm, which is always formed from the
upper polar nucleus only, the egg apparatus
becoming disorganized.
Fruits and Seeds
As the development of embryo and endosperm
proceeds within the embryo-sac, its wall
enlarges and the commonly absorbs the substance
of the nucleus (which is likewise enlarging)
to near its outer limit, and combines with
it and the integument to form the seed-coat;
or the whole nucleus and even the integument
may be absorbed. In some plants the nucleus
is not always absorbed, but itself becomes
a seat of deposit of reserve-food constituting
per sperm which may coexist with endosperm,
as in the water-lily order, or may alone
form a food-reserve for the embryo, as in
Cana. Endospermic food-reserve has evident
advantages over perispermic, and the latter
is comparatively rarely found and only in
non-progressive series. Seeds in that endosperm
or per sperm or both exist are commonly
called aluminous or endospermic, those in
which are neither is found are termed exalbuminous
or exendospermic. These terms, are extensively
used by systematizes, only refer, however,
to the grosser features of the seed, and
indicate the more or less evident occurrence
of a food-reserve; many so-called exalbuminous
seeds show to microscopic examination a
distinct endosperm which may have other
than a nutritive function.
The presence
or absence of the endosperm, its relative
to the amount when present, and the position
of the embryo within it, are very much valuable
characters for the distinction of orders
and groups of orders. Meanwhile the ovary
wall has to develop form the fruit or per
carp, the structure of which is closely
related with the manner of distribution
of the seed. Frequently the influence from
of fertilization is felt beyond the ovary,
and other parts of the flower take part
of formation in the fruit, as the floral
receptacle in the apple, strawberry and
others.
The character of the seed-coat bears
a definite relation to that of the fruit.
Their function is the twofold one of protecting
the embryo and of aiding the in dissemination;
they could also directly promote germination.
If the fruit is a dehiscent one and seed
is therefore soon exposed, the seed-coat
has to provide for the protection in the
embryo and may also have to secure dissemination. On the other hand, indehiscent fruits discharge
these functions for the embryo, and the
seed-coat is very slightly developed.
With
multi-seeded
fruits, multiple grains of pollen
could be necessary for syngamy with each
ovule. The process is easy to visualize
if one looks at maize silk that is the female
flower of corn. Pollen from the tassel
male flower) falls on the straight sticky
external portion of the silk, and then pollen
tubes grow up the silk to the attached ovule.
The dried silk remains inside the husk of
the ear as the seeds mature, so one can
carefully remove the husk to show the floral
structures. The development of the flesh
fruit is the proportional to the percentage
of fertilized ovules.
