The Fruit

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The Fruit The fruit is the mature gynoecium along
with accessory tissues. As the fertilised egg
develops, the gynoecium becomes the sole or main
component of the flower. Perianth and stamens
usually whither and fall. The style dries up,
except in those species in which it functions in
fruit dispersal. The ovary enlarges, but may be
associated with noncarpellary tissue (accessory
tissue) which dominates in the mature
fruit. Parthenocarpy fruits develop without
fertilisation may occur in citrus, pepper,
pumpkin, tomato and produces seedless fruits.
Seedless fruit may develop from aborted embryos,
e.g. in cherry, grape, peach. Extracarpellary
tissues receptacle in strawberry, bracts in
pineapple, calyx in the mulberry, and floral tube
or receptacle in fruits derived from epigynous
flowers, such as the apple and pumpkin. Simple
fruit formed from a single pistil (one carpel or
two or more united carpels as in the bean pod,
tomato, plum. Aggregate fruit formed from an
apocarpous gynoecium with each carpel maintaining
its separate identity, e.g. raspberry,
strawberry. Multiple fruit derived from an
inflorescence (combined gynoecia of many flowers)
e.g. mulberry, pineapple. Accessory fruits (false
or spurious fruits) any of the above fruit types
which contains extracarpellary tissue, e.g. the
apple is a simple accessory fruit strawberry an
aggregate accessory fruit mulberry a multiple
accessory fruit. If the fruit is defined to
include any associated extracarpellary tissue
then four fruit types encompass all fruit 1.
Aggregate fruit carpels not united. 2. Unit
fruit carpels united. 3. Free fruit formed from
a superior ovary. 4. Cup fruit formed from an
inferior ovary embedded in a cup of noncarpellary
tissue or from a superior ovary enclosed in a
hypanthium. Combining these classifications 1.
Aggregate free fruit derived from an apocarpous
hypogynous flower. 2. Unit free fruit from a
syncarpous hypogynous flower. 3. Aggregate cup
fruit from an apocarpous perigynous flower. 4.
Unit cup fruit from a syncarpous epigynous
flower. Fruitlet an individual carpel in an
aggregate fruit.
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The Fruit Wall The pericarp is the mature ovary
wall, the whole fruit wall is the pericarp plus
accessory tissue. The pericarp may consist of
three distinct layers (exocarp or epicarp,
mesocarp and endocarp). Fruit Types Dry
Fruit Dehiscent Fruit Dehiscent fruit commonly
contain several seeds and may develop from a
single carpel (follicle, legume) or from more
than one carpel (capsule, silique). In
monocarpellary dehiscent fruit, the break may
occur longitudinally through the suture joining
carpel margins, the back of the carpel or both
simultaneously. In syncarpous fruits with
parietal placentation, dehiscence may occur
through the suture between two carpels or through
the backs of carpels. In syncarpous fruits with
axile placentation, the separation along the
lines of union (septae) of joining carpels
(septicidal dehiscence) may be combined with a
breaking away from the central column. Dehiscence
through the backs of carpels opens the locules
(loculicidal dehiscence). Longitudinal breaks may
occur in other places. Some fruits undergo
longitudinal circular dehiscence involving all
carpels (circumscissile dehiscence) or through
pores (poricidal dehiscence). Many dehiscent
fruit are called pods. Legumes (many Fabaceae)
derived from a superior ovary formed from a
single carpel. Dehisces along the carpel margins
and the median vein. In Glycine (soybean) pods,
the exocarp is the outer epidermis and
hypodermis, both with thickened walls the
mesocarp is parenchyma and the endocarp includes
several layers of sclerenchyma and the inner
epidermis. The cells in the hypodermis have their
long axes perpendicular to those of the
sclerenchyma. Thus, when the fruit dries, the
outer and inner pericarp layers shrink in
different directions, setting up stresses which
open the fruit. This may be enhanced by the
differing orientation of cellulose microfibrils
in different layers of sclerenchyma. The valves
may separate explosively and become twisted. In
Phaseolus (bean) pod, the parenchyma beneath the
hypodermis contains chloroplasts with starch
granules and encloses a network of small vascular
bundles near the sclerenchyma interconnecting the
median and lateral bundles and makes some beans
stringy. The inner epidermis of Phaseolus
divides to form an inner layer of
non-photosynthetic parenchyma, making the green
pod a useful vegetable. In some legumes (Pisum,
Vicia faba) the inner parenchyma produces
multicellular hairs that extend into the locules
and are thought to maintain optimum humidity
inside the locules. Capsule (silique) many
Brassicaceae consists of two carpels
(bicarpellary) joined margin to margin and a
false partition (derived from the marginal
placentae) which divides the locule in two. The
exocarp and mesocarp are thin-walled and the
endocarp is sclerenchymatic. A rib develops
around the partition, along the juncture of the
carpels. The carpels separate along the suture,
leaving the seeds attached to the ribbed edge or
frame (replum) of the partition. E.g. shepherds
purse (Capsella).
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Follicle a dry monocarpellary, superior,
one-chambered fruit that dehisces by one suture
only. E.g. the simple follicle of madar
(Calotropis). Most often follicles are aggregates.
Diagrams of cross sections of dry dehiscent
fruits illustrating three types of fruits, still
unopened (A, D, G), and examples of dehiscence of
such fruits (B-C, E-F, H-I). A, single carpel. D,
three carpels, parietal placentation. G, three
carpels, axial placentation. The median and two
lateral bundles are indicated in each carpel. The
median bundles are shown split in two in C, F, I.
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Indehiscent Fruit Usually derived from an ovary
in which only one seed develops, even if more
than one locule is present. The pericarp
resembles a seed coat in structure and may
largely replace the seed coat (achene of
Asteraceaea) or fuse with the seed coat
(caryopsis of Poaceae). Achene (Asteraceae)
develops from an inferior ovary (a cypsella).
One-chambered, one-seeded fruit developing from a
superior or inferior monocarpellary ovary and
with a pericarp free from the seed coat. The
floral tube forms extracarpellary tissue
(indistinct from the pericarp). The seed coat
(derived from one integument) has a thick-walled
outer epidermis and the fruit wall is reduced to
an outer sclerified tissue and some parenchyma.
E.g. the simple achenes of hogweed (Boerhaavia)
most are aggregate. Caryopsis (grasses,
monocarpellary, superior, pericarp fused with
seed coat). The pericarp and remains of the seed
coat from the outer layers of the wheat
caryopsis. The layers are outer epidermis
(covered by cuticle), one or more layers of
parenchyma, partly resorbed parenchyma, cross
cells (elongated transverse to the grain long
axis and having thick lignified walls) and
remains of an inner epidermis (lignified cells
elongated parallel with the grain long axis
tube cells). The outer integument disintegrates
and the inner becomes altered and compressed it
is covered by cuticle on both sides and contains
a fatty pigment. The endosperm forms 83 of the
fruit and contains starch and protein. The
outermost endosperm layer is the aleurone layer
which contains lipids and proteins. Wheat bran
14 of the grain, includes the pericarp, remnants
of the nucellus and integuments, and the aleurone
layer. Wheat germ the oily wheat
embryo. Glutens wheat proteins that affect bread
making along with glycolipids which interact with
the glutens. Zea (including maize) the outer
pericarp consists of cells with thick pitted
walls and is compressed. The central pericarp
disintegrates. The inner pericarp remains
thin-walled and is compressed, stretched or torn.
The integuments disintegrate completely A cuticle
occurs between the thick-walled nucellar
epidermis and the pericarp. Cuticular layers in
the seed coat are derived from the nucellar
epidermis and the integuments and are fused into
one layer. In wheat, a strand of pigmented tissue
interrupts this layer and this may allow water to
enter the seed (?). Millet (Echinochloa utilis)
a small gap in the cutinised seed coat occurs at
the base of the caryopsis and contains two cell
types nucellar cells and cells similar to those
in the wheat pigment strand. The aleurone cells
opposite these nucellar cells are transfer cells
with wall ingrowths. Similar aleurone transfer
cells occur in Zea. Cypsela a dry, one-chambered
and one-seeded fruit developing from an inferior,
bicarpellary ovary with free pericarp and seed
coat, e.g. Compositae sunflower,
marigold. Samara. A dry, indehiscent, one or two
seeded fruit developing from a superior bi- or
tricarpellary ovary, with one or more flattened,
wing-like outgrowths, e.g. ash. The wings develop
from the pericarp and the fruit splits into
fruitlets, each enclosing a seed. Samaroids
winged fruit, but with the wings derived from
dry, persistent sepals, e.g. wood-oil tree
(Dipterocarpus), sal tree (Shorea) and Hopea.
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Caryopsis (A) of wheat (Triticum) and parts of
its pericarp in longitudinal section (B) and
surface views (C, D).
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Samaras of elm, maple and sycamore.
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Nut. A dry, one-chambered and one-seeded fruit,
developing from a superior, bi- or polycarpellary
ovary, with a hard and woody pericarp. E.g.
chest-nut (Castanea), oak, beech. Schizocarp
(Schizocarpic fruit) Lomentum. A dry indehiscent
legume with partitions between the seeds and one
seed per compartment. The fruit splits
transversely into one-seeded fruitlets, e.g. gum
tree (Acacia), sensitive plant, Indian telegraph
plant (Desmo-dium gyrans). Cremocarp. A dry,
indehiscent, two-chambered fruit developing from
an inferior, bicarpellary ovary. The fruit splits
into indehiscent one-seeded fruitlets, called
mericarps. The mericarps remain attached to the
prolonged end (carpophore) of the axis. E.g.
Umbelliferae coriander (Coriandrum), cumin
(Cuminum), anise or fennel (Foeniculum), carrot
(Daucus). E.g. the cremocarp of Carum (Apiaceae)
derived from an inferior ovary. Pericarp and
accessory tissue can not be distinguished. The
mericarps separate such that the united lateral
bundles and associated tissue form a column,
forked at the top. Double Samara. Maple (Acer)
develops from a superior, bicarpellary ovary.
Splits into two samaras when mature, each with
one wing and one seed. Regma. A dry, indehiscent
fruit developing from a syncarpous pistil. It
splits away from the central axis into cocci,
each coccus containing one carpel and one or two
seeds. The dry pericarp decays to liberate the
seeds, e.g. caster (Ricinus), Geranium. Carcerule.
A small, dry, indehiscent, four-chambered fruit
developing from a superior, bicarpellary pistil
and is enclosed by a persistent calyx and splits
into four nutlets, each enclosing a single seed.
E.g. Labiatae.
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Fleshy Fruits Drupe (stone-fruit). A fleshy fruit
with one or more chambers and one or more seeds
developing from a monocarpellary or syncarpous
pistil. The pericarp consists of epicarp (skin),
mesocarp (often fleshy) and the endocarp (hard
and stony). E.g. mango (Mangifera), plum and
peach (Prunus), coconut-palm (Cocos). The fruit
of Prunus originates from a single carpel in a
perigynous flower. The ventral suture between the
carpel margins is often visible as an indentation
in plums, peaches and nectarines. The thin
exocarp consists of epidermis and subepidermal
collenchyma, the mesocarp is fleshy and the
sclerenchymatous endocarp is stony. Bacca
(Berry). A many-seeded fleshy or pulpy fruit
developing from a single carpel or a syncarpous
pistil, e.g. tomato, gooseberry, grapes, banana.
The seeds separate from the placentae in the ripe
fruit and remain free in the pulp. Date palm is a
one-seeded berry. The banana (Musa acuminata)
fruit arises from an inferior tricarpellary ovary
with axile placentation. In seedless
parthenocarpic bananas the ovules degenerate and
the locules are filled with starch-rich pulp
originating from the pericarp and dividing walls.
Very little pulp is produced in seeded varieties
as the mature seeds fill the locules. The
parenchyma of banana fruit walls contains
numerous vertical vascular bundles and
laticifers. Inside this zone occurs aerenchyma,
and then a zone with horizontal vascular bundles
that connect with the pericarp vertical bundles
and the central carpellary bundles. In the tomato
(Lycopersicon esculentum) the berry has no rind.
Wild types and cherry tomatoes have two carpels,
but other cultivated forms have a variable larger
number of carpels. The fleshy tissue includes the
pericarp, the partitions and the placentae (which
are axile, but fill most of the locular space).
Placental tissue that invades spaces among the
ovules becomes gelatinous when the fruit is
mature. Absorption of red light by phytochrome
and ethylene synthesis cause the green
chloroplasts to change in to red
chromoplasts. Pepo. A fleshy, pulpy many-seeded
fruit which develops from an inferior, unilocular
or trilocular syncarpous pistil with parietal
placentation. E.g. Cucurbitaceae (cucurbits)
cucumber, melon, squash, etc. The seeds lie in
the pulp, but remain attached to the placentae.
The boundary between carpellary and
extracarepellary tissues is not discernible. A
single-layered epidermis is covered with cuticle
and has stomata. The subepidermal consists of
parenchyma or collenchyma. The subepidermal
parenchyma give the fruit its colour and may have
green chloroplasts or yellow chromoplasts. Fibers
and phloem strands may be present and in some
there is a layer of sclereids. Beneath this
sclerenchyma is parenchyma which extends to the
centre of the fruit at maturity (cucumber, water
melon) or id torn and replaced by a central
cavity (Cucurbita maxima, muskmelon). The inner
epidermis of the endocarp may cover the seeds in
a membranous layer. In water melon the red colour
results from pigment crystals inside
chromoplasts. Pome. An inferior bilocular or
multilocular, fleshy, syncarpous fruit surrounded
by the thalamus. The thalamus constitutes the
fleshy, edible part. E.g. apple, pear.
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The fruit of Pyrus (P. malus, apple P. communis,
pear), the pome, arises from an inferior ovary
and the bulk of the flesh is extracarpellary.
This extracarpellary tissue is interpreted as
either part of the floral tube or hypanthium or
as derived from the receptacle. The ovary
consists of five carpels united to form axile
placentation. The outer epidermis is covered with
a thick cuticle of overlapping platelets of wax.
Stomata and trichomes occur in young fruit. The
stomata are later replaced by lenticels. In
russeting apples patches of cork develop in the
outer layers of the apple. The subepidermal
tissue is compact and has thickened walls. The
skin is made up of the epidermis and
subepidermis. The skin of red varieties contains
anthocyanins and carotenoid-rich chromoplasts
also contribute to the red colour. The flesh is
mostly parenchyma with large air spaces and
contains the main bundles which give off
anastomosing branches throughout the flesh. The
core consists of parenchyma enclosing the median
and lateral carpellary bundles and an endodermis
of sclereids lining the locules. Each locule has
two or more seeds. Clusters of sclereids in the
flesh of the pear.
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Transactions of fruits of Musca acuminata
(banana, A, B) and Lycopersicon esculentum (C).
A, parthenogenesis carpic fruit with ovarian
cavities occluded by pulp derived from pericarp
and partitions. B, seeded fruit with ovarian
cavities occupied by seeds and small amount of
pulp. C, the placentae have occluded the locules
and have embedded the ovules. The tissue among
the ovules of gelatinous in mature fruit. Solid
black lines indicate lacunar spaces.
Hesperidium. A superior, multilocular, fleshy
fruit developing from a syncarpous pistil with
axile placentation. The endocarp (and mesocarp)
projects inwards to form distinct chambers and
the fused epicarp and mesocarp form the rind,
e.g. Citrus with about ten carpels. In lemon the
exocarp (flavedo, the yellow tissue) consists of
cuticle-covered outer epidermis and compact
subepidermal parenchyma with oil glands and
crystal-containing cells. The mescocarp of lemon
(albedo or white tissue) consists of parenchyma
with large intercellular spaces and aerenchyma
and contains a vascular network. The endocarp
consists of inner epidermis and a few layers of
compact parenchyma. (Peel exocarp and all but
innermost layer of mesocarp). The endocarp
produces the juice sacs (multicellular
club-shaped structures with long stalks) that
fill the locules. In a mature juice sac a
cuticularised epidermis encloses large vacuolated
cells containing juice. Photosynthetic
parenmchyma gives the exocarp of unripe fruit its
green colour. These chloroplasts become
chromoplasts in the ripe fruit (the Valencia
orange is orange in winter and turns green again
in spring). Balausta. Inferior, many-chambered
and many-seeded fruit developing from a
syncarpous pistil with usually two whorls of
basal carpels within the receptacle, forming two
layers of chambers. The pericarp is tough and
leathery and the chambers are made of thin-walled
carpels, e.g. pomegranate (Punica granatum).
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A, transection of ovary of Citrullus vulgaris
(watermelon). The dashed lines indicate regions
of union of carpels, solid lines delimit margins
of carpels within each carpel and the placentae
from the fruit wall. The lateral bundles of
contiguous carpels are united. B, transection of
one carpel with one placenta freed from the
surrounding tissue. C, a diagram interpreting the
arrangement of carpels in a cucurbitaceous ovary.
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Fruit of Prunus domestica (prune). A,
longitudinal and B, transverse sections of the
ovary. Ovarian cavity in solid black. C, D, outer
part of pericarp 6 weeks after full bloom (C) and
2 weeks after abscission. Disorganised
protoplasts and partly collapsed cell walls in D.
E, F, inner part of endocarp. E, 6 weeks after
full bloom, at completion of cell division. F, 8
weeks after full bloom, at beginning of
lignification. C-F from transverse sections.
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Citrus fruit. A, B, young ovary from flower of
Citrus aurantifolia (lime) in longitudinal (A)
and transverse (B) sections. C, part of
transection of young fruit of Citrus sinensis
(orange) including one carpel. Juice sacs in
early stage of growth. D, diagram of orange fruit
including two carpels and part of a third. Juice
sacs fill the locules.
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Aggregate Fruits An aggregate of simple fruits
borne on a single flower is called an
etaerio. Etaerio of follicles, with two or more
follicles, e.g. madar (Calotropis) and periwinkle
(Vinca). Etaerio of achenes. E.g. Clematis,
Rannunculus, strawberry, rose, lotus. Etaerio of
drupes. E.g. raspberry (Rubus) with small drupes
(drupels or drupelets) aggregated together in a
fleshy thalamus. Each drupelet has a stony
endocarp of various layers of differently
oriented elongated sclereids and the succulent
pulp is the parenchymatous mesocarp. The exocarp
bears epidermal hairs that hold the drupelets
together at maturity. Etaerio of berries. Berries
embedded in the fleshy thalamus, e.g.
custard-apple (Annona squamosa) or with distinct
and separate berries, e.g. Polyatlhia,
Artabotrys. Multiple or Composite Fruits
(infructescence) A composite fruit develops from
an inflorescence. Sorosis. A multiple fruit
developing from a spike or spadix. The flowers
fuse together by their succulent sepals and the
axis grows fleshy or woody and the whole
inflorescence forms into a compact mass, e.g.
pineapple. Mulberry is a sorosis with the fleshy
part made of loosely attached sepals. Syconus.
Develops from a hollow, pear-shaped, fleshy
receptacle which encloses a number of minute male
and female flowers. The fleshy receptacle
encloses a number of achenes, e.g. Ficus (e.g.
fig, banyan).
Longitudinal section of the flower of Rosa.
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Blackberry (Rubus) a, the polycarpellate
gynoecium b, carpel c, median section of the
aggregate fruit d, young drupelet e, mature
drupelet h, hypanthium s, sepals st, stamens.
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Dispersal of seeds and Fruit Seeds and Fruits
Dispersed by Wind Wings. E.g. maple and sycamore
(Acer), elm and birch. Parachute mechanism. In
many Compositae, the calyx forms a pappus of
hairs. The pappus opens out in an umbrella-like
manner when the fruit detaches from the parent
plant. E.g. cotton. Censer mechanism. The seeds
are discharged from a dehisced fruit when the
fruit is shaken by the wind. E.g. poppy
(Papaver), loofah (Luffa). Hairs. The seeds of
madar (Caloptropis), milkweed (Asclepias) and
cotton have hairs either in one or two tufts or
all over the seed. Persistent styles. In Clematis
the styles persist and are very feathery. Light
seeds and fruits. Orchids have the smallest
seeds. Millions of dust-like seeds are produced
in a capsule. The fruits of some grasses are also
very light. Seeds and Fruits Dispersed by
Water The fibrous coat of the coconut is a
flotation device that carries the coconuts across
the sea. In the double coconut (coc de mer,
Lodoicea maldivica) the fruit weighs 18 kg and
may be up to a metre in length and takes 6-10
years to ripen. In lotus, the spongy thalamus,
bearing fruits and its hemispheric top, floats in
water. The seeds of water lily are small and
light and also have an aril enclosing air and so
they can float on water. Seeds Dispersed by
Explosive Fruits Scatter seeds a few yards from
the parent plant, e.g. balsam (Impatiens),
wood-sorrel (Oxalis). Some seeds of the explosive
fruits of Acanthaceaea are provided with
jaculators (curved hooks) that suddenly
straighten and help seed ejection. The fruits may
burst open in either dry or wet conditions,
depending on species. Camels foot climber
(Bauhinia vahlii) has long explosive pods
sometimes exceeding 30 cm in length. Seeds and
Fruits Dispersed by Animals Hooked fruits. Hooks,
bristles, spines, barbs, stiff hairs etc. allow
the fruit to adhere to fur and clothes. Sticky
fruits. These have sticky glands, e.g. Plumbago,
mistletoe (Viscum). Fleshy fruits and edible
fruits. Animals eat the fruit and seeds pass out
with their faeces, e.g. guava, grape, fig, dates,
plums. Squirrels may disperse acorns and
hazelnuts when they bury them for a winter store
which they later forget about or do not need.