Transcript Slide 1

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.
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 nonphotosynthetic 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. shepherd’s purse (Capsella).
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.
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, oneseeded 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. woodoil tree (Dipterocarpus), sal tree (Shorea) and Hopea.
Caryopsis (A) of wheat (Triticum) and parts of its pericarp in longitudinal section (B) and surface views (C, D).
Samaras of elm,
maple and
sycamore.
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.
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.
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.
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).
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.
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.
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.
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.
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.
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. Camel’s 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.