FRUIT AND SEEDS

FRUIT

A true fruit is formed as a result of cell division expansion and differentiation in the ovary wall (placenta). The ovary is transformed into fruit as a result of stimuli received from pollination and developing seeds. The wall of ovary develops into pericarp of  the fruit that is differentiated into epicarp, mesocarp, and endocarp. During pollination the pollen grains release auxin that induces the fruit development.

STRUCTURE OF FRUIT

A true fruit consists of two main parts the seed and the pericarp (fruit flesh). The pericarp consists of three layers- upper epicarp, middle mesocarp and inner endocarp.

TYPES OF FRUITS

Fruits are of three main types

1-SIMPLE FRUITS;  

the fruits that develop from a single monocarpellary or multicarpellary syncarpous ovary are called simple fruits. These are further of two types:

A-dry simple fruits; these fruits have dry pericarp not differentiated into three layers. these are further of three types.

(i)-Dehiscent dry fruits;

Legume; a fruit developed from a monocapellary superior ovary which dehisces from both the sutures into two halves -pea

Follicle;- which dehisces from one suture only –calotropis

Siliqua; develop from a bicapellary superior ovary with a replum or false septum. Dehisces along two sutures -brassica

Capsule; dehiscent dry fruit which dehisces along more than two suture in different planes.

(ii)-Schizocarpic dry fruits

Lomentum; a legume like fruit that dehisces transversely into one seeded indehiscent compartments -tamarindus

Cremocarp; develops from an inferior ovary, splits longitudinally into two indehiscent halves called mericarps -cariandrum sativum.

Regma; it breaks into as many segments as there are carpels -ricinus.

Carcerule; here it breaks into four indehiscent parts with one seed per locule-ocimum.

(iii)Indehiscent dry fruits

Achene; a small indehiscent one seeded fruit with a hard and leathery pericarp that remains free from seed coat -mirabilis jalapa.

Caryopsis; small indehiscent one seeded fruit with a hard and leathery pericarp fused with seed coat - wheat, rice

Cypsela; a one seeded fruit that develops from a multicarpellary ovary with persistent calyx - tridex

Nut; large indehiscent one seeded fruit with a hard and stony fruit wall - chesnut.

Samara; a dry indehiscent one seeded fruit in which pericarp is modified into wings- chilbil.

B-Fleshy simple fruits; fruits with fleshy pericarp distinguished into epicarp mesocarp and endocarp;

Berry; a fleshy many seeded fruit with massive juicy and pulpy pericarp-tomato grapes.

Hesperidium; a fleshy many seeded fruit with a firm hard and leathery pericarp- citrus, lemon, orange

Pepo;  a large fleshy fruit with pulpy pericarp -melon, cucumber

Drupe;-  a fleshy one seeded fruit with the inner hard stony pericarp enclosing a seed-mango, wall nut, peach, cherry.

Balausta; a fleshy fruit with many chambers and many seeds -pomegranate

Amphisarca; a fleshy fruit with woody pericarp and edible placenta- wood apple

Pome; a false fruit that develops from thalamus with true fruits inside containing seeds-apple pear etc

2-AGGREGATE FRUITS

Fruit developed from multicarpellary apocarpous ovary; comprised of many fruitlets;

Etaerio of follicles; fruit consisting of many follicles arranged on thalamus-calotropis

Etaero of achenes;  an aggregate of achenes -strawberry

Etaerio of drupes; an aggregate of drupes- rasberry

Etaerio of berries; an aggregate of berries -anona squamosal

MULTIPLE OR COMPOSITE FRUITS;

the fruits that develop from the complete inflorescence;

Sorosis; fruit developed from a spike or spadix inflorescence - pine apple, mulberry

Syconus; fruit developed from Hypanthodium inflorescence - ficus.  

                                                     SEED

The seed is a developed ovule. Development of the fertilized ovule into the mature seed involves several different parts. From the outside to inwards these are as follows:

• The zygote develops into an embryo.
• The integuments of the ovule become the seed coat of the mature seed. This sometimes consists of two distinct coverings, a typically firm outer coat, the testa, and a generally thin, membranous inner coat, the tegmen.
• The nucellus may persist in some genera as a thin layer - the perisperm
• The endosperm accumulates reserves of food and its fullest development is rich in carbohydrates, fats, proteins and growth
• The funiculus forms the stalk of the seed. Hilum marks the point of attachment to the stalk
• Micropyle remains as a pore on the surface of seed

Structure of Dicot and Monocot Seeds

Structure of Dicot non-endospermic seed (bean seed):

The seeds of bean like those of other legumes are formed within the pod, which is a ripened ovary. The seed is attached to the inside of the pod by the funiculus or seed stalk. When the seeds are shed, the funiculus breaks off, leaving a prominent scar, the hilum. Just below the hilum can be seen the

micropyle and above the hilum is the ridge formed by the raphe. The bean seed has two seed coats outer testa and inner tegmen. Each seed encloses an embryo. The bulk of embryo consists of large cotyledons which stores Most of the food of seed. On the side of the seed, opposite the raphe at the micropylar end the cotyledons form cotyledonary node. Attached to it is found the radical.  Plumule has differentiated two well-defined leaves which fold over the growing tip. These become the first true leaves of the bean plant on germination. The portion between radical and cotyledonary node is called hypocotyl. The portion between plumule and hypocotyl is called epicotyls. In this seed and in all seeds of this type, there is no endosperm, this tissue is already consumed by the developing embryo.

Structure of Monocot, endospermic grain (maize grain ):

It is one seeded fruit called caryopsis or grain because pericarp (fruit wall) is fused with testa. Seed coat is the outer brownish layer of the grain. In this, seed and fruit walls are fused together. Endosperm comprises the major part of grain and is filled with reserve food. It is composed of two regions Outer single layered aleurone layer mainly made up of aleurone proteins. Inner starchy endosperm. It is separated from embryo by a layer called epithelium. Embryo contains a single lateral cotyledon called scutellum and embryo axis with plumule and radicle at its two ends. Root cap protects the tip of radicle. Radicle is surrounded by a protective sheath called coleorhiza. Plumule is also protected by a covered sheath known as coleoptile.

INFLORESCENCE

INFLORESCENCE

A flowering shoot or an axis bearing a cluster of flowers is called an inflorescence. The main axis of inflorescence is called peduncle. When the flowers occur singly they are called solitary. Solitary flowers may be born at apex (solitary terminal) or at axils of leaves (solitary axillary).

Types of inflorescence;- There are three types of inflorescence; racemose Inflorescence, cymose Inflorescence, and special Inflorescence

A)-Racemose Inflorescence;

When the flowers are born laterally or in axils it is called racemose inflorescence. The arrangement of flowers can be either acropetal or centripetal. Here the flowers are not born at apex of a branch or main stem. Racemose Inflorescence can be simple or compound.

a)-Simple racemose Inflorescence; in simple racemose the peduncle remains unbranched. It is further of following types

(i)-Spike;- when the stalk less sessile flowers are born on a common axis in acropetal succession it is called spike (amaranthus)

(ii)-Catkin or ament;- a hanging or pendulous spike Inflorescence consisting of small unisexual flowers is called catkin inflorescence (salix, morus alba)

(iii)-Spadix;-  a spike Inflorescence covered by thick and large brackets (leaves), (maize, banana).

(iv)-Corymb;- here the lower peduncles are long and upper are short in such a way so that all the flowers come to same level (candytuff)

(v)-Umbel;- here the peduncles are of same length and arise from same point- (centella asiatica).

(vi)-Capitulum;- here the peduncle is flat and is called receptacle which bears small flowers called florets in centripetal manner (sunflower).

b)-Compound racemose Inflorescence;- it is a kind of racemose Inflorescence in which the peduncle is unbranched. it is further of following types

(i)-Compound Panicle;- here the axis is branched and flowers are born in acropetal succession (gold mohur, yucca)

(ii)-Compound spike;- here the axis is branched and lateral branches bear sessile flowers in acropetal succession (grasses like wheat).

(iii)-Compound spadix;- it is like simple spadix except that the axis is branched here (coconut).

(iv)-Compound corymb;-. It is simple corymb type but axis is branched. Each branch has its own corymb.

(v)-Compound umbel; here also the axis is branched in a simple umbel (coriander, carrot).  

B)-CYMOSE INFLORESCENCE

In this type of Inflorescence the peduncle or main axis terminates into a flower and further growth takes place by lateral branches each below the terminal flower. It is further of three types;-

a)-Uniparous or monochasial cyme;- here a single branch arises below each flower. If the branching occurs alternatively it is called scorpoid and if it occurs on the same side of axis it is called helicoid.

b)-Biparous or dichasial;- here a pair of branches arise below a terminal flower  (jasmine)

c)-Multiparous or polychasial;- in this type more than two branches arise below each terminating flower (calotropis).

C)-SPECIAL TYPES OF INFLORESCENCE;

1)-Hypanthodium; it is a special type of inflorescence formed by the condensation of main axis into a cup or flask shaped receptacle enclosing flowers in cymose groups. The opening of this cavity is called ostiole. It is found in ficus carica (fig), ficus religiosa (peepal) and in ficus bengalensis.

2)-Cyathium; it is a special type of inflorescence formed by the condensation of peduncle into a small conical receptacle surrounded by a Cyathium involucres. The involucres contain long female and short male flowers. It is found in euphorbia pulcherrima.

3)-Verticillaster- it is a special type of inflorescence formed by the condensation of two cymose inflorescences into a head in the axils of two opposite leaves at the node. The flowers are sessile zygomorphic, bilabiate forming a cluster or verticel round the stem. It is found in lamiaceae family-ocimum sanctum, salvia.

MORPHOLOGY OF LEAF

THE LEAF –

Leaf is a green, dissimilar exogenous lateral flattened outgrowth which is borne on the node of a stem or its branches and is specialized to perform photosynthesis. Leaves originate from shoot apical meristem and areNArranged in an  acropetal order.

A typical leaf consists of three parts- Leaf base (phyllopodium, hypopodium), Petiole (mesopodium), Lamina (epipodium). Leaf is attached with stem by Leaf Base which may bear two small leaf like structure called stipule.

The pattern of arrangement of leaves on the stem or branch is called Phyllotaxy. The phyllotaxy is of three types;-

Alternate or spiral;- when one leaf is born at each node and are arranged alternately to form a spiral arrangement around the stem. Each spiral is called a genetic spiral and each vertical row is called an orthostichies. If the leaves are arranged in one circle and two vertical rows the phylotaxy is called distichous or is written as ½(spirals or circles/rows). Tristichous 1/3, pentastichous 2/5, octostichous- 3/8.

The arrangement is made as 1/2+1/3+2/5+3/8+5/13 this series is called schimper-brown series.

Opposite;- when two leaves are born at each node opposite to each other so that only rows are formed. The two leaves may form only two rows (superposed) or may form four rows (decussate).

Whorled;- when more then two leaves are born at each node it is called whorled.

VENATION

The Middle prominent vein of a leaf is called mid vein. Veins provide rigidity to the leaf blade and act as channels for transport of water and minerals. The arrangement of vein and veinlets in the lamina is called venation. It is of two types;-

Reticulate venation;- the Veinlets are irregularly distributed and form a network. It is present in all Dicotyledons like Gram, Pea, Beans, and Mango etc. if the lamina has only one principal vein, the venation is called reticulate unicostate (mango). If the lamina has more than one principal veins then it is called reticulate multicostate (smilex, cucurbita, papaya etc).

Parallel venation;- in this type the Veins are parallel to one another and do not form a network. It is present in Monocotyledons like Grass, Banana, Rice etc. if there is a single principal vein with lateral veins running parallel it is called parallel unicostate (banana). If more then one principal vein then it is called parallel multicostate (maize,sugarcane).

TYPES OF LEAVES;-A leaf having a single or undivided lamina it is called Simple leaf. The incisions do not touch the mid rib. Example- Mango, Guava etc.

When the incision of lamina reach up to the midrib and breaking it into a number of leaflets it is called Compound leaves.

In a Pinnately compound leaves, a number of leaflets are present on common axis called rachis. Example- Neem.

In Palmately compound leaves, the leaflets are attached at common point. Example- Silk cotton.

MEDIFICATION OF LEAVES;-

in plants like wild pea, gloriosa superba, clematis the leaves get modified into long, thin, and coiled tendrils. In nepenthes the petiole and rachis (clementis)  gets modified into tendril.

In some plants like agemon, opuntia, and barberry the leaves get modified into spines.

In plants like bignonia, asparagus the leaves get modified into hard and tapering hooks.

In some plants like accasia and parkinsonia the lamina is absent or becomes reduced. The rachis and the petiole gets modified into a leaf like structures called phyllodes.

In some plants like nepenthes (pitcher plant) and sarracenia the lamina of the leaf gets modified into a pitcher and petiole into a lid. In utricularia the leaf lobes get modified into sac like traps called bladders which trap insects. In drosera the leaf lamina gets modified into a spoon shaped blade that bears little touch sensitive glandular hairs which trap the pry. These plants are called insect eating or insectivorous plants.

MORPHOLOGY OF STEM

THE STEM

The ascending part of axis bearing branches, leaves, flowers and fruits is called stem. It develops from Plumule of the embryo.

Stem bears nodes and internodes. The regions of stem where leaves are born are called nodes and portion between two nodes are called internodes.

The main function of stem is spreading lateral organs like branches, leaves, (exogenous in origin) flowers and fruits. It also conducts water and minerals and products of photosynthesis from roots to leaves.

Some stem perform special functions like storage of food, support, protection and vegetative propagation.

BRANCHING OF THE STEM;- in some plants stem remains unbranched called caudex or columnar stems (coconut, maize, sugar cane) in angiosperms the branching of stem is always lateral. The lateral branching can be;-

Racemose brancing (monopodial); the terminal bud grows indefinitely and branching occurs in acropetal succession (youngest at apex and oldest at base) e.g eucalyps.

Cymose branching: when the apical bud stops its growth or gets modified into flower, tendril etc and further growth occurs by branching. If growth occurs by only a single branch (sympodial branch) it is called monochasial. The sympodial branches may arise on both the sides of main axis (scorpoid) like in grape vine or on one side (helicoid) like in saraca indica.

If the further growth of plant takes place by two branches it is callked dichaesial branching like in four o clock plant(mirabilis jalapa), viscum, silene etc  and if it takes place by more than two branches it is called polychasial branching like in euphorbia, croton, nerium odoratum etc and the axis is said to be multipodial.

Types or forms of stems;-

1) Reduced stems:- when the stem is reduced and not differentiated into nodes and internodes like in wollfia, onion, garlic etc it is called reduced stem.

2) Erect stems:- where the stems are upright and vertically erect. If the nodes are swollen and give a jointed appearance to stem than it is called culm stem like in bamboo. If stem is thick at base and tapering towards apex with branches in acropetal succession it is called excurrent like in cedrus deodara, pinus spp. If the main stem stops growth after some height and further growth occurs due to the activity of branches making a dome like appearance it is called decurrent stem like in banyan tree, walnut etc.

3) weak stems;- these are thin soft and delicate stems. These can be upright or prostrate.

The upright stems may coil around a support (due to a special type of growth called nutation) are called twiners like in clitoria or lab lab.

Some weak upright stems climb over a support called climbers with the help of tendrils (vitis,smilex, clematis) adventitious roots (piper betel), curved pricles or hooks (rose).

The prostrate stems spread over the ground. Such stems may trail along the surface without rooting at intervals called trailers or stragglers like in tridex bessela. Some prostrate stems root at nodes and creep along the surface called creepers.

Many creepers develop adventitious roots downward into soil  after some elongation and an aerial branch upright, such creepers are called runners. The elongation of internodes in runners occur in all directions like in dramun (cynodon dactylon) oxalis etc.

In strawberry fragaria vesica, mentha the stem initially grows upward then arches down to develop new plant, such creeping stems are called stolons. In some plants like water hyacinth the stems creep only one inter-node and develop crown of adventitious roots bellow and a tuft of leaves above, such creeping stems are called offsets.

MODIFICATIONS OF STEM;-

underground stem modifications;-

In some plants the main stem or its branches lie below the soil and are called underground stems. these stems are non green and resemble roots. The underground stems are of the following types

Sucker;- in some plants like menthe, chrysanthemum  a branch of stem grows obliquely below the surface of soil and emerges out in the form of new shoot.

Rhizome;- (figA-B) in some perennial plants like ginger, nelumbo nucifera, alocasia indica the stem remains underground, stores food, and swells. It develops roots below and reduced shoots above it. These bear nodes and internodes and are non-photosynthetic.

Corms;- fig ( A-E) in some plants like saffron (crocus sativus), amorphophallus the stem is underground, spherical, swollen with a large apical bud over and small adventitious roots bellow. The parent corms develop daughter corms which develop into new shoots.

Tubers;- in some plants like potato the stems branch underground and each branch swells at its tip which forms a tuber. In tubers the nodes are represented by small depressions called eyes. The eyes are more crowded at apical end (rose end) and less at distal or stolen end (heel end). Tubers store food in the form of starch.

Bulb;- in some plants like onion garlic the stem is much reduced in the form of a small disc with several fleshy scales enclosing a terminal bud.

AERIAL MODIFIED STEMS;-

Stem tendrils;- in some plants like cucurbita, antigonon, passiflora the stems are modified into long thin and spirally coiled climbing organs called tendrils.

Stem thorns;- in some plants like citrus, pomegranate the stem is modified into stif, pointed and sharp structures called thorns. Thorns are protective in function.

Phylloclades;- in some plants like opuntia, euphorbia royleana the stem gets modified into flattened or cylindrical, green leaf like structures called phylloclades. The leaves in such plants are modified into spines.

Cladode;- in some plants like asparagus, ruscus the stems and branches of unlimited growth get modified into small one internode long sylendrical (asparagus) or flat (ruscus) leaf like structures called cladode. These are born in clusters.