Category: Biology

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Seed Various Types and its Significance

Do all fruits contain seeds? No, triploid fruits do not. The seed is a fertilized mature ovule which possess an embryonic plant, usually stores food material and has a protective coat. After fertilization, changes occur in various parts of the ovule and transforms into a seed.

Types of Seed

I. Based on the number of cotyledons two types of seeds are recognized.

(i) Dicotyledonous Seed:
Seed with two cotyledons.

(ii) Monocotyledonous Seed:
Seed with one cotyledon.

II. Based on the presence or absence of the endosperm the seed is of two types.

(i) Albuminous or Endospermous Seed:
The cotyledons are thin, membranous and mature seeds have endosperm persistent and nourishes the seedling during its early development. Example: Castor, sunflower, maize.

(ii) Ex-albuminous or Nonendospermous Seed:
Food is utilized by the developing embryo and so the mature seeds are without endosperm. In such seeds, colyledons store food and become thick and fleshy. Example: Pea, groundnut.

Significance of Seeds:

1. The seed encloses and protects the embryo for next generation.
2. It contains food for the development of embryo.
3. It is a means for the dispersal of new individuals of the species.
4. A seed is a means for perpetuation of the species. It may lie dormant during unfavorable conditions but germinates on getting suitable conditions.
5. Seeds of various plants are used as food, both for animals and men.
6. They are the basis of agriculture.
7. Seeds are the products of sexual reproduction so they provide genetic variation and recombination in a plant.
   

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Fruits – Structure of Fruits and its Types

We know about several kinds of fruits, but by botanical study we will be surprised to know the types of fruits and how they are produced by plants. Fruits are the products of pollination and fertilization, usually containing seeds inside.

In common person’s perspective a fruit may be defined as an edible product of the entire gynoecium and any floral part which is sweet, juicy or fleshy, coloured, aromatic and enclosing seeds. However the fruit is a fertilized and ripened ovary. The branch of horticulture that deals with the study of fruits and their cultivation is called pomology.

Structure of Fruit

Fruit has a fruit wall. It is otherwise called pericarp. It is differentiated into outer epicarp, middle mesocarp and inner endocarp. The inner part of the fruit is occupied by the seed.

Types of Fruit

Fruits are classified into three types:

Simple Fruits
The fruits are derived from a single ovary of a flower Example: Mango, Tomato. Simple fruits are classified based on the nature of pericarp as follows.

A. Fleshy Fruit

The fruits are derived from single pistil where the pericarp is fleshy, succulent and diffrentiated into epicarp, mesocarp and endocarp. It is subdivided into the following.

(a) Berry:
Fruit develops from bicarpellary or multicarpellary, syncarpous ovary. Here the epicarp is thin, the mesocarp and endocarp remain undifferentiated. They form a pulp in which the seeds are embedded. Example: Tomato, Grapes, Brinjal.

(b) Drupe:
Fruit develops from monocarpellary, superior ovary. It is usually one seeded. Pericarp is differentiated into outer skinny epicarp, fleshy and pulpy mesocarp and hard and stony endocarp around the seed. Example: Mango, Coconut.

(c) Pepo:
Fruit develops from tricarpellary inferior ovary. Pericarp turns leathery or woody which encloses, fleshy mesocarp and smooth endocarp. Example: Cucumber, Watermelon, Bottle gourd, Pumpkin.

(d) Hesperidium:
Fruit develops from multicarpellary, multilocular, syncarpous, superior ovary. The fruit wall is differentiated into leathery epicarp with oil glands, a middle firous mesocarp. The endocarp forms distinct chambers, containing juicy hairs. Example: Orange, Lemon.

(e) Pome:
It develops from multicarpellary, syncarpous, inferior ovary. The receptacle also develops along with the ovary and becomes fleshy, enclosing the true fruit. In pome the epicarp is thin skin like and endocarp is cartilagenous. Example: Apple, Pear.

(f) Balausta:
A fleshy indehiscent fruit developing from multicarpellary, multilocular inferior ovary whose pericarp is tough and leathery. Seeds are attached irregularly with testa being the edible portion. Example: Pomegranate.

B. Dry Fruit

They develop from single ovary where the pericarp is dry and not differentiated into epicarp, mesocarp and endocarp. It is further subdivided into three types.

1. Dry Dehiscent Fruit

Pericarp is dry and splits open along the sutures to liberate seeds. They can be classified into following types.

(a) Follicle:
Fruit develops from monocarpellary, superior ovary and dehisces along one suture. Example: Calotropis.

(b) Legume or Pod:
Fruit develops from monocarpellary, superior ovary and dehisces through both dorsal and ventral sutures. Example: Pisum.

(c) Siliqua:
Fruit develops from bicarpellary, syncarpous, superior ovary initially one chambered but subsequently becomes two chambered due to the formation of false septum (replum). The fruit dehisces along two suture. Example: Brassica.

(d) Silicula:
Fruit similar to siliqua but shorter and broader. Example: Capsella.

(e) Capsule:
Fruit develops from multicarpellary, syncarpous, superior ovary. Based on the dehiscence pattern they are divided into.

(i) Septicidal:
Capsule splitting along septa and valves remaining attached to septa. Example: Aristolochia.

(ii) Loculicidal:
Capsule splitting along locules and valves remaining attached to septa. Example: Abelmoschus.

(iii) Poricidal:
Dehiscence through terminal pores. Example: Papaver.

2. Dry Indehiscent Fruit

Dry fruit which does not split open at maturity. It is subdivided into.

(a) Achene:
Single seeded dry fruit developing from single carpel with superior ovary. Achenes commonly develop from apocarpous pistil, Fruit wall is free from seed coat. Example: Clematis, Delphinium.

(b) Cypsela:
Single seeded dry fruit, develops from bicarpellary, syncarpous, inferior ovary with reduced scales, hairy or feathery calyx lobes. Example: Tridax.

(c) Caryopsis:
It is a one seeded fruit which develops from a monocarpellary, superior ovary. Pericarp is inseparably fused with seed. Example: Oryza.

(d) Nut:
They develop from mulicarpellary, syncarpous, superior ovary with hard, woody or bony pericap. It is a one seeded fruit. Example: Anacardium.

(e) Samara:
A dry indehiscent, one seeded fruit in which the pericarp devlops into thin winged structure around the fruit. Example: Acer.

(f) Utricle:
They develop from bicarpellary, unilocular, syncarpus, superior ovary with pericarp loosely enclosing the seeds. Example: Chenopodium.

3. Schizocarpic Fruit

This fruit type is intermediate between dehiscent and indehiscent fruit. The fruit instead of dehiscing, splits into number of segments, each containing one or more seeds. They are of following types.

(a) Cremocarp:
Fruit develops from bicarpellary, syncarpous, inferior ovary and splitting into two one seeded segments known as mericarps. Example: Coriander.

(b) Carcerulus:
Fruit develops from bicarpellary, syncarpous, superior ovary and splitting into four one seeded segments known as nutlets. Example: Leucas.

(c) Lomentum:
The fruit is derived from monocarpellary, unilocular ovary. A leguminous fruit, constricted between the seeds to form a number of one seeded compartments that separate at maturity. Example: Mimosa.

(d) Regma:
They develop from tricarpellary, syncarpous, superior, trilocular ovary and splits into one­seeded cocci which remain attached to carpophore. Example: Ricinus.

Aggregate Fruits

Aggregate fruits develop from a single flower having an apocarpous pistil each of the free carpel develops into a simple fruitlet. A collection of simple fruitlets makes an Aggregate fruit. An individual ovary develops into a drupe, achene, follicle or berry. An aggregate of these fruits borne by a single flower is known as an etaerio. Example: Annona, Polyalthia.

Multiple or Composite Fruit:
A Multiple or composite fruit develops from the whole inflorescence along with its peduncle on which they are borne.

(a) Sorosis:
A fleshy multiple fruit which develops from a spike or spadix. The flowers fused together by their succulent perianth and at the same time the axis bearing them become fleshy or juicy and the whole inflorescence forms a compact mass. Example: Pine apple, Jack fruit.

(b) Syconus:
A multiple fruit which develops from hypanthodium inflorescence. The receptacle develops further and converts into fleshy fruit which encloses a number of true fruit or achenes which develops from female flower of hypanthodium inflorescence. Example: Ficus

Functions of Fruit

• Edible part of the fruit is a source of food and gives energy for animals.
• They are source of many chemicals like sugar, pectin, organic acids, vitamins and minerals.
• The fruit protects the seeds from unfavourable climatic conditions and animals.
• Both fleshy and dry fruits help in the dispersal of seeds to distant places.
• In certain cases, fruit may provide nutrition to the developing seedling.
• Fruits provide source of medicine to human.

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Construction of Floral Diagram and Floral Formula

A floral formula is a simple way to explain the salient features of a flower. The floral diagram is a representation of the cross section of the flower. It represents floral whorls arranged as viewed from above. Floral diagram shows the number and arrangement of bract, bracteoles and floral parts, fusion, overlapping and placentation. The branch that bears the flower is called mother axis.

The side of the flower facing the mother axis is called posterior side. The side facing the bract is the anterior side. The members of different floral whorls are shown arranged in concentric rings.

Br: Bracteate
Ebr: Ebracteate
Brl: Bracteolate
Ebrl: Ebracteolate
⊕: Actinomorphic
%: Zygomorphic

K: Calyx, K₅ five sepals, aposepalous, K(₅) five sepals synsepalous.
C: Corolla, C₅ five petals, apopetalous, C(₅) five petals sympetalous C(₂₊₃) corolla bilabiate with upper lib two lobes.
A: Androecium A₃ three stamens free, A₂₊₂, Stamens 4, two whorls (didynamous) each whorl two stamens (free)

A₍₉₎₊₁ 
Stamens ten, two bundles (diadelphous) 9 stamens unite to form one bundle, 1 stamen form another bundle.

Epipetalous represented by an arc.

A⁰: Staminode(sterile stamen)
G. Gynoecium or pistil – G₂ – Carpels two, free (apocarpous)
G₍₃₎ – Carpels three, united (syncarpous)
G₀ – Pistillode (sterile carpel)

\(\underline{G}\) – Superior Ovary
G inferior Ovary
G- – Semi-inferior ovary
∞ – Indefinite number of units

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Gynoecium – Definition, Types and its Structure

Gynoecium or pistil is the female reproductive part of the flower. A pistil consists of an expanded basal portion called the ovary, an elongated section called a style and an apical structure that receives pollen called a stigma. Ovary with stipe is called stipitate ovary.

Carpel:
They are components of a gynoecium. Gynoecium is made of one or more carpels. Carpels may be distinct or connate.

Number of Carpel

Fusion of Carpels

It is an important systematic character. Apocarpous gynoecium is generally thought to be ancestral condition in Angiosperms.

Number of Locules

Ovary bears ovules on a specialized tissue called placenta. A septum is a crosswall or partition of ovary. The walls of ovary and septa form a cavity called locule. Like that tetralocular and pentalocular ovaries are present according to the locule numbers four or fie. More than one locule ovaries are called plurilocular.

Extension of the Condensed Internode of the Receptacle

1. Anthophore:
The internodal elongation between calyx and corolla. Example: caryophyllaceae (Silene conoidea)

2. Androphore:
The internodal elongation between the corolla and androecium. Example: Grewia.

3. Gynophore:
The internodal elongation between androecium and gynoecium. Example: Capparis.

4. Gynandrophore or Androgynophore:
The unified internodal elongation between corolla and androecium and androecium and gynoecium. Example: Gynandropsis.

Ovary Position

The position or attachment of ovary relative to the other floral parts. It may be classified into

1. Superior Ovary:
It is the ovary with the sepals, petals and stamens attached at the base of the ovary.

2. Inferior Ovary:
It is the ovary with the sepals, petals and stamens attached at the apex of the ovary.

3. Half-inferior Ovary:
It is the ovary with the sepals, petals and stamens or hypanthium attached near the middle of the ovary.

Perianth/Androecial Position on Thalamus:
It describes placement of the perianth and androecium relative to the ovary and to a hypanthium, if present (Figure 4.25).

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Androecium – Definiton of Androecium and its Various Types

Androecium:
Third whorl of flower is the male reproductive part of the flower. It is composed of stamens (microsporophylls).

Each Stamen consist of 3 parts:

• Filament
• Anther
• Connective

Anther:
Upper swollen part with microsporangia.

Filament:
Stalk of stamen

Connective:
Tissue connecting anther lobes with filament

Anther typically contains two compartments called thecae (singular theca). Each theca consists of two microsporangia. Two microsporangia fused to form a locule. Sterile stamens are called Staminodes. Example: Cassia. Distinct: stamens which do not fuse to one another. Free: stamens which do not fuse with other parts of flower. Apostemonous: flowers with stamens that are free and distinct.

Fusion of Stamens:
The fusion of stamens fusing among themselves or with other parts of flower. They are of two types.

• Connation and
• Adnation

1. Connation:
Refers to the fusion of stamens among themselves. It is of 3 types:-

• Adelphy
• Syngenecious
• Synandrous

Adelphy:
Filaments connate into one or more bundles but anthers are free. It may be the following types.

(i) Monadelphous:
Filaments of stamens connate into a single bundle. Example: Malvaceae (Chinarose, Cotton).

(ii) Diadelphous:
Filaments of stamens connate into two bundles. Example: Fabaceae (pea) and Clitoria.

(iii) Polyadelphous:
Filaments connate into many bundles. Example: Citrus, Bombax

Syngenesious:
Anthers connate, filaments free. Example: Asteraceae.

Synandrous:
Filaments and anthers are completely fused. Example: Coccinea.

2. Adnation:
Refers to the fusion of stamens with other flral parts. Epipetalous: Stamens are adnate to petals. Example: Brinjal, Datura.

a. Episepalous:
Stamens are adnate to sepals. Example: Grevillea (Silver oak)

b. Epitepalous (Epiphyllous):
Stamens are adnate to tepals. Example: Asparagus.

c. Gynostegium:
Connation product of stamens and stigma is called gynostegium. Example: Calotropis and Orchidaceae.

d. Pollinium:
Pollen grains are fused together as a single mass Example: Calotropis

Arrangement of stamens relate to length of stamens:

1. Didynamous:
Four stamens of which two with long fiaments and two with short filaments. Example: Ocimum

2. Tetradynamous:
Six stamens of which four with long filaments and two with short filaments. Example: Brassica.

3. Heterostemonous:
Stamens are of different lengths in the same flower. Example: Cassia.

Anther Types

1. Monothecal:
One lobe with two microsporangia. They are kidney shaped in a cross section. Example: Malvaceae

2. Dithecal:
It is a typical type, having two lobes with four microsporangia. They are butterfly shaped in cross section. Example: Solanaceae.

Anther Attachment

1. Basifixed:
(Innate) Base of anther is attached to the tip of filament. Example: Datura.

2. Dorsifixed:
Apex of filament is attached to the dorsal side of the anther. Example: Hibiscus.

3. Versatile:
Filament is attached to the anther at midpoint. Example: Grasses.

4. Adnate:
Filament is continued from the base to the apex of anther. Example: Nelumbo

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Accessory Organs – Everything You Need to Know

Arrangement of Whorls

The position of perianth (sepals, petals, tepals) parts relative to one another is called perianth arrangement.

1. Cyclic or Whorled:
All the floral parts are arranged in definite whorls. Example: Brassica.

2. Acyclic or Spiral:
The floral parts are arranged in spirals on the elongated fleshy torus. Example: Magnolia.

3. Spirocyclic or Hemicyclic:
Some parts are in whorls and others parts are in spirals. Example: Annona, Polyalthia

Calyx

Calyx protects the flower in bud stage. Outermost whorl of flower is calyx. Unit of calyx is sepal. Normally green in colour.

1. Fusion:

a. Aposepalous (Polysepalous):
The flower with distinct sepals. Example: Brassica, Annona.

b. Synsepalous:
The flower with united or fused sepals. Example: Hibiscus.

2. Duration of Floral Parts:

What is the green part of brinjal fruit? Have you seen similar to this in any other fruits?

a. Caducous or Fugacious Calyx:

Calyx that withers or falls off during the early development stage of flower. Example: Papaver.

b. Deciduous:

Calyx that falls soon after the opening of flower (anthesis) Example: Nelumbo.

c. Persistant:

Calyx that persists and continues to be along with the fruit and forms a cup at the base of the fruit. Example: Brinjal.

d. Accrescent:

Calyx that is persistent, grows along with the fruit and encloses the fruit either completely or partially. Example: Physalis.

3. Shapes of Calyx

Have you noticed the shoe flower’s calyx? It is bell shaped called Campanulate. The fruiting calyx is urn shaped in Withania and it is called urceolate. In Datura calyx is tube like and it is known as tubular. Two lipped calyx is present in Ocimum. Sometimes calyx is coloured and called petaloid. Example: Saraca and Mussanda. In Tridax, calyx is modified into hair like structures are called pappus.

Corolla

Corolla is the most attractive part in majority of the flowers and is usually brightly coloured. Corolla helps to display the flower and attracts the pollinators.

1. Fusion:

a. Apopetalous (Polypetalous):

Petals are distinct. Example: Hibiscus.

b. Sympetalous (Gamopetalous):

Petals are fused. Example: Datura.

Perianth

Can you recall the term homochlamydeous? Undifferentiated calyx and corolla in a flower is called perianth. Each member is called tepal. If the tepals are distinct they are called Apotepalous (Polyphyllous). Example: Allium sativum. Fused tepals are called Syntepalous. (Gamophyllous). Example: Allium cepa.

Aestivation:

Arrangement of sepals and petals in the flower bud is said to be aestivation.

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Flower – Definition of Flower and its Various Types

In a plant, which part would you like the most? Of course, it is a flower, because of its colour and fragrance. The flower is a significant diagnostic feature of angiosperms. It is a modified condensed reproductive shoot. The growth of the flower shoot is determinate.

Whorls of Flower

There are two whorls, accessory and essential. Accessory whorl consists of calyx and corolla and essential whorl comprises of androecium and gynoecium. Flower is said to be Complete when it contains all four whorls. An Incomplete flower is devoid of one or more whorls.

Flower Sex
Flower sex refers to the presence or absence of androecium and gynoecium within a flower.

1. Perfect or Bisexual:
If a flower contains both androecium and gynoecium it is called as a perfect flower.

2. Imperfect or Unisexual:
When the flower contains only one of the essential whorls is called Imperfect flower. It is of two types:

(i) Staminate Flowers:
Flowers with androecium alone.

(ii) Pistillate Flowers:
Flowers with gynoecium alone.

Plant Sex

Plant sex refers to the presence and distribution of flowers with different sexes in an individual plant.

1. Hermaphroditic:
All the flwers of the plant are bisexual.

2. Monoecious:
Both male and female flowers are present in the same plant Example: Coconut.

3. Dioecious:
Male and Female flowers are present on separate plants. Example: Papaya, Palmyra.

4. Polygamous:
The condition in which bisexual and unisexual (staminate/pistillate) flowers occur in a same plant is called polygamous. Example: Musa, Mangifera.

Flower Symmetry

What is the radius of a circle? Cut a paper into round shape, fold it so as to get two equal halves. In how many planes will you get equal halves? In how many planes you can divide a cucumber in two equal halves? A flower is symmetrical when it is divided into equal halves in any plane running through the center. Flower symmetry is an important structural adaptation related to pollination systems.

1. Actinomorphic (or) Radial or Polysymmetric:
The flower shows two mirror images when cut in any plane or radius through the centre. Normally there are more than two planes of symmetry. Example: Hibiscus, Datura.

2. Zygomorphic (Bilateral Symmetry) or Monosymmetric:
The flower can be divided into 2 equal halves in only one plane. Zygomorphic flower can efficiently transfer pollen grains to visiting pollinators. Example: Pisum, Bean.

3. Asymmetric (Amorphic):
Flower lacks any plane of symmetry and cannot be divided into equal halves in any plane. Parts of such flowers are twisted. Example: Canna indica.

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Inflorescene Types and its Characteristics

Have you seen a bouquet being used during functions? Group of flowers arranged together on our preference is a bouquet. But an inflorescence is a group of flowers arising from a branched or unbranched axis with a definite pattern.

Function of inflorescence is to display the flowers for effective pollination and facilitate seed dispersal. The grouping of flowers in one place gives a better attraction to the visiting pollinators and maximize the energy of the plant.

Types of Inflorescence

Based On Position

Have you ever noticed the inflorescence arising from different positions? Where is the inflorescence present in a plant? Apex or axil? Based on position of inflorescences, it may be classified into three major types. They are,

Terminal:
Inflorescence grows as a part of the terminal shoot. Example: Raceme of Nerium oleander.

Axillary:
Inflorescence presents in the axile of the nearest vegetative leaf. Example: Hibiscus rosa-sinensis

Cauliflorous:
Inflorescence developed directly from a woody trunk. Example: Theobroma cocoa, Couraupita guinensis. Observe the inflorescence of Jackfruit and Canon ball tree. Where does it arise?

Based on Branching Pattern and Other Characters

Inflorescence may also be classified based on branching, number and arrangement of flowers, and some specialized structures.

I. Indeterminate (Racemose)
II. Determinate (Cymose)

III. Mixed Inflorescence:
Inflorescence of some plants show a combination of indeterminate and determinate pattern.

IV. Special Inflorescence:
Inflorescence which do not confine to these patterns

I. Racemose

The central axis of the inflorescence (peduncle) possesses terminal bud which is capable of growing continuously and produce lateral flowers is called Racemose inflorescence. Old flowers are at the base and younger flowers and buds are towards the apex. It is further divided into 3 types based on growth pattern of main axis.

1. Main Axis Elongated

The axis of inflorescence is elongated and contains pedicellate or sessile flowers on it. The following types are discussed under main axis elongated type.

a. Simple Raceme:
The inflorescence with an unbranched main axis bears pedicellate flowers in acropetal succession. Example: Crotalaria retusa, Mustard.

b. Spike:
Spike is an unbranched indeterminate inflorescence with sessile flowers. Example: Achyranthes.

c. Spikelet:
Literally it is a small spike. The Inflorescence is with branched central axis. Each branch is a spikelet. Sessile flowers are formed in acropetal succession on the axis.

A pair of inflorescence bracts called glumes is present at the base. Each sessile flower has a lemma (bract) and a palea (bracteole). Tepals reduced to colourless scaly leaves (lodicule). Each flower has stamen and pistil only. Example: Paddy, Wheat.

d. Catkin:
Pendulous spikes with a long and drooping axis bearing small unisexual or bisexual flowers. It is also called ament. Example: Acalypha hispida, Prosopis juliflora.

e. Spadix:
An inflorescence with a fleshy or thickened central axis that possesses many unisexual sessile flowers in acropetal succession. Usually female flowers are found towards the base and male flowers are found at the apex. Entire inflorescence is covered by a brightly coloured or hard bract called a spathe. Example: Amorphophallus, Colocasia.

f. Panicle:
A branched raceme is called panicle. Example: Mangifera, neem. It is also called Compound raceme or Raceme of Racemes.

2. Main axis shortened:

Inflorescence with reduced growth of central axis. There are two types, namely corymb and umbel.

a. Corymb:
An inflorescence with shorter pedicellate flowers at the top and longer pedicellate flowers at the bottom. All flowers appear at the same level to form convex or flat topped racemose inflorescence. Example: Caesalpinia. Compound corymb: A branched corymb is called Compound corymb. Example: Cauliflower.

b. Umbel:
An inflorescence with indeterminate central axis and pedicellate flowers arise from a common point of peduncle at the apex. Example: Allium cepa.

Compound Umbel:
It is a branched umbel. Each smaller unit is called umbellule. Example: Daucas carota, Coriandrum sativum.

3. Main Axis Flattened:
The main axis of inflorescence is mostly flattened (convex or concav) or globose. A head or capitulum is determinate or indeterminate, group of sessile or sub sessile flowers arising on a receptacle, often subtended by an involucre.

a. Head:
A head is a characteristic inflorescence of Asteraceae and is also found in some members of Rubiaceae and Mimosaceae. Torus contains two types of florets:

• Disc floret or tubular floret
• Ray floret or ligulate floret. Based on the type of florets present, the heads are classified into two types.

(i) Homogamous Head:
This type of inflorescence exhibits single kind of florets. Inflorescence has disc florets alone. Example: Vernonia, Ray florets alone. Example: Launaea.

(ii) Heterogamous Head:
The inflorescence possesses both types of florets. Example: Helianthus, Tridax.

Disc florets at the centre of the head are tubular and bisexual, whereas the ray florets found at the margin of the head which are ligulate and pistilate (unisexual).

II. Cymose Inflorescence

Central axis stops growing and ends in a flower, further growth is by means of axillary buds. Old flowers present at apex and young flowers at base.

1. Simple Cyme (Solitary):
Determinate inflorescence consists of a single flower. It may be terminal or axillary. Example: terminal in Trillium grandiflrum and axillary in Hibiscus.

2. Monochasial Cyme (Uniparous):
The main axis ends with a flower. From two lateral bracts, only one branch grows further. It may be Helicoid or Scorpioid.

a. Helicoid:
Axis develops on only one side and forms a coil structure atleast at the earlier development stage. Example: Hamelia, potato.

b. Scorpioid:
Axis develops on alternate sides and often becomes a coiled structure. Example: Heliotropium.

3. Simple Dichasium (Biparous):
A central axis ends in a terminal flower; further growth is produced by two lateral buds. Each cymose unit consists of three flowers of which central one is old one. Ths is true cyme. Example: Jasminum.

4. Compound Dichasium:
It has many flowers. A terminal old flower develops lateral simple dichasial cymes on both sides. Each compound dichasium consists of seven flowers. Example: Clerodendron. A small, simple dichasium is called cymule

5. Polychasial Cyme (Multiparous):
The central axis ends with a flower. The lateral axis branches repeatedly. Example: Nerium

III. Mixed Inflorescence

Inflorescences in which both racemose and cymose patterns of development occur in a mixed manner. It is of the following two types.

1. Thyrsus:
It is a ‘Raceme of cymes’. Indefinite central axis bears lateral pedicellate cymes, (simple or compound dichasia). Example: Ocimum.

2. Verticillaster:
Main axis bears two opposite lateral sessile cymes at the axil of the node, each of it produces monochasial scorpioid lateral branches so that flowers.

IV. Special Inflorescence

The inflorescence that do not show any of the development pattern types are classified under special type of inflorescence.

1. Cyathium:
Cyathium inflorescence consists of small unisexual flowers enclosed by a common involucre which mimics a single flower. Male flowers are organised in a scorpioid manner. Female flower is solitary and centrally located on a long pedicel.

Male flower is represented only by stamens and female flower is represented only by a pistil. Cyathium may be actinomorphic (Example: Euphorbia) or zygomorphic (Example: Pedilanthus). Nectar is present in involucre.

2. Hypanthodium:
Receptacle is a hollow, globose structure consisting of unisexual flowers present on the inner wall of the receptacle. Receptacle is closed leaving a small opening called ostiole which is covered by a series of bracts. Male flowers are present nearer to the ostiole, female and neutral flowers are found in a mixed manner from middle below. Example: Ficus sp. (Banyan, Fig and Pipal).

3. Coenanthium:
Circular disc like fishy open receptacle that bears pistillate flowers at the center and staminate flowers at the periphery. Example: Dorstenia.

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Leaf Definition – Characteristics and Various Types of Functions

Leaves are green, thin flattened lateral outgrowths of the stem. Leaves are the primary photosynthetic organs and the main site of transpiration. All the leaves of a plant together are referred to as phyllome.

I. Characteristics of Leaf

• Leaf is a lateral appendage of the stem.
• It is borne at the node of the stem.
• It is exogenous in origin.
• It has limited growth.
• It does not posses apical bud.
• It has three main parts namely, leaf base, petiole and lamina.
• Lamina of the leaf is traversed by vascular strands, called veins.

II. Functions of the Leaf

Primary Functions

• Photosynthesis
• Transpiration
• Gaseous exchange
• Protection of buds
• Conduction of water and dissolved solutes.

Secondary Functions

1. Storage:
Example: Aloe, Agave.

2. Protection:
Example: Opuntia, Argemone mexicana.

3. Support:
Example: Gloriosa, Nepenthes.

4. Reproduction:
Example: Bryophyllum, Begonia, Zamia.

Parts of the Leaf

Three main parts of a typical leaf are:

1. Leaf base (Hypopodium)
2. Petiole (Mesopodium)
3. Lamina (Epipodium)

I. Leaf Base (Hypopodium)

The part of the leaf attached to the node of the stem is called leaf base. Usually it protects the growing buds at its axil.

Pulvinus:
In legumes leaf base become broad and swollen which is known as pulvinus. Example: Clitoria, Lablab, Cassia, Butea.

Sheathing Leafbase:
In many monocot families such as Arecaceae, Musaceae, Zingiberaceae and Poaceae the leafbase extends into a sheath and clasps part or whole of the internode. Such leafbase also leave permanent scars on the stem when they fall.

II. Petiole (Stipe or Mesopodium)

It is the bridge between lamina and stem. Petiole or leaf stalk is a cylindrical or sub cylindrical or flattened structure of a leaf which joins the lamina with the stem. A leaf with petiole are said to be petiolate. Example: Ficus, Hibiscus. Leaves that do not possess petiole is said to be sessile. Example: Calotropis.

III. Lamina (Leaf Blade)

The expanded flat green portion of the leaf is the blade or lamina. It is the seat of photosynthesis, gaseous exchange, transpiration and most of the metabolic reactions of the plant. The lamina is traversed by the midrib from which arise numerous lateral veins and thin veinlets. The lamina shows great variations in its shape, margin, surface, texture, colour, venation and incision.

Stipules

In most of the dicotyledonous plants, the leaf base bears one or two lateral appendages called the stipules. Leaves with stipules are called stipulate. The leaves without stipules are called exstipulate or estipulate. The stipules are commonly found in dicotyledons. In some grasses (Monocots) an additional out growth is present between leaf base and lamina. It is called Ligule.

Sometimes, small stipule like outgrowths are found at the base of leaflets of a compound leaf. They are called stipels. The main function of the stipule is to protect the leaf in the bud condition.

Venation

The arrangement of veins and veinlets on the leaf blade or lamina is called venation. Internally, the vein contains vascular tissues. Conventionally venation is classified into two types namely, Reticulate venation and Parallel venation.

I. Reticulate Venation

In this type of venation leaf contain a prominent midrib from which several secondary veins arise that branch and anastomose like a network. This type of venation is common in all dicot leaves. It is of two types.

1. Pinnately Reticulate Venation (Unicostate):
In this type of venation there is only one midrib in the centre which forms many lateral branches to form a network. Example: Mangifera indica.

2. Palmately Reticulate Venation (Multicostate):
In this type of venation there are two or more principal veins arising from a single point and they proceed outwards or upwards. The two types of palmate reticulate venation are

(i) Divergent Type:
When all principal veins originate from the base and diverge from one another towards the margin of the leaf as in Carica papaya.

(ii) Convergent:
When the veins converge to the apex of the leaf, as in Indian plum (Zizyphus), bay leaf (Cinnamomum).

II. Parallel Venation

Veins run parallel and do not form a prominent reticulum. It is a characteristic feature of monocot leaves. It is classified into two sub types.

1. Pinnately Parallel Venation (Unicostate)
When there is a prominent midrib in the center, from which arise many veins perpendicularly and run parallel to each other. Example: Musa, Zinger.

2. Palmate Parallel Venation (Multicostate)
In this type several veins arise from the tip of the petiole and they all run parallel to each other and unite at the apex. It is of two sub types.

(i) Divergent Type:
All principal veins originate from the base and diverge towards the margin, the margin of the leaf as in fan palm (Borassus flabelliformis)

(ii) Convergent Type:
All principal veins run parallel to each other from the base of the lamina and join at the apex as in Bamboos, rice, water hyacinth.

Phyllotaxy

The mode of arrangement of leaves on the stem is known as phyllotaxy (Gk. Phyllon = leaf; taxis = arrangement). Phyllotaxy is to avoid over crowding of leaves and expose the leaves maximum to the sunlight for photosynthesis. The four main types of phyllotaxy are:-

1. Alternate
2. Opposite
3. Ternate
4. Whorled.

1. Alternate Phyllotaxy

In this type there is only one leaf per node and the leaves on the successive nodes are arranged alternate to each other. Spiral arrangement
of leaves show vertical rows are called orthostichies. They are of two types.

(a) Alternate spiral:
In which the leaves are arranged alternatively in a spiral manner. Example: Hibiscus, Ficus.

(b) Alternate Distichous or Bifarious:
In which the leaves are organized alternatively in two rows on either side of the stem. Example: Monoon longifolium (Polyalthia longifolia).

2. Opposite Phyllotaxy

In this type each node possess two leaves opposite to each other. They are organized in two different types.

(i) Opposite Superposed:
The pair of leaves arranged in succession are in the same direction, that is two opposite leaves at a node lie exactly above those
at the lower node. Example: Psidium (Guava), Quisqualis (Rangoon creeper).

(ii) Opposite Decussate:
In this type of phyllotaxy one pair of leaves is placed at right angles to the next upper or lower pair of leaves. Example: Calotropis, Ocimum.

3. Ternate Phyllotaxy

In this type there are three leaves attached at each node. Example: Nerium

4. Whorled (Verticillate)

Type of phyllotaxy. In this type more than three leaves are present in a whorl at each node forming a circle or whorl. Example: Allamanda.

Leaf Mosaic

In leaf mosaic leaves tend to fit in with one another and adjust themselves in such a way that they may secure the maximum amount of sunlight with minimum amount of overlapping. The lower leaves have longer petioles and successive upper leaves possess shorter petioles. Example: Acalypha.

Leaf Type

The pattern of division of a leaf into discrete components or segments is termed leaf type. Based on the number of segments

I. Simple Leaf

A leaf is said to be simple when the petiole bears a single lamina; lamina may be entire (undivided) Example: Mango or incised to any depth but not upto the midrib or petiole. Example: Cucurbita.

II. Compound Leaf

Compound leaf is one in which the main rachis bears more than one lamina surface, called leaflets. Compound leaves have evolved to increase total lamina surface. There is one axillary bud in the axil of the whole compound leaf. The leaflets however, do not possess axillary buds.

1. Pinnately Compound Leaf

A pinnately compound leaf is defined as one in which the rachis, bears laterally a number of leaflets, arranged alternately or in an opposite manner, as in Tamarindus, Cassia.

(i) Unipinnate:
The rachis is simple and unbranched which bears leaflets directly on its sides in alternate or opposite manner. Example: Rose, Neem. Unipinnate leaves are of two types.

• When the leaflets are even in number, the leaf is said to be paripinnate. Example: Tamarindus.
• When the leaflets are odd in number, the leaf is said to be imparipinnate. Example: Azadirachta (Neem).

(ii) Bipinnate:
The primary rachis produces secondary rachii which bear the leaflets. The secondary rachii are known aspinnae. Number of pinnae varies depending on the species. Example: Delonix.

(iii) Tripinnate:
When the rachis branches thrice the leaf is called tripinnate. (i.e) the secondary rachii produce the tertiary rachii which bear the leaflets. Example: Moringa.

(iv) Decompound:
When the rachis of leaf is branched several times it is called decompound. Example: Daucus carota, Coriandrum sativum.

2. Palmately Compound Leaf

A palmately compound leaf is defined as one in which the petiole bears terminally, one or more leaflets which seem to be radiating from a common point like fingers from the palm.

(i) Unifoliolate:
When a single leaflet is articulated to the petiole is said to be unifoliolate. Example: Citrus.

(ii) Bifoliolate:
When there are two leaflets articulated to the petiole it is said to be bifoliolate. Example: Zornia diphylla

(iii) Trifoliolate:
There are three leaflets articulated to the petiole it is said to be trifoliolate. Example: wood apple (Aegle marmelos), Clover (Trifolium).

(iv) Quadrifoliolate:
There are four leaflets articulated to the petiole it is said to be quadrifoliolate. Example: Paris quadrifolia, Marsilia

(v) Multifoliolate or Digitate:
Five or more leaflets are joined and spread like fingers from the palm, as in Cleome pentaphylla, Bombax ceiba.

Modifiation of Leaf
The main function of the leaf is food preparation by photosynthesis. Leaves modified to perform some specialized functions. They are described below.

I. Leaf Tendrils

In some plants stem is very weak and hence they have some special organs for attachment to the support. So some leaves are partially or wholly modified into tendril. Tendril is a slender wiry coiled structure which helps in climbing the support. Some of the modification of leaf tendrils are given below:

Entire leaf:
Lathyrus

Stipules:
Smilax

Terminal Leaflet:
Naravelia

Leaf Tip:
Gloriosa

Apical Leaflet:
Pisum

Petiole:
Clematis.

II. Leaf Hooks

In some plants, leaves are modified into hook-like structures and help the plant to climb. In cat,s nail (Bignonia unguis-cati) an elegant climber, the terminal leaflets become modified into three, very sharp, stiff and curved hooks, very much like the nails of a cat. These hooks cling to the bark of a tree and act as organs of support for climbing. The leaf spines of Asparagus also act as hooks.

III. Leaf Spines and Prickles

Leaves of certain plants develop spinesent structures. Either on the surface or on the margins as an adaptation to herbivory and xeric conditions. Example: Zyzypus Argemone mexicana (Prickly poppy), Solanum trilobatum. In xerophytes such as Opuntia (Prickly pear) and Euphorbia leaves and stipules are modified into spines.

Prickles are small, sharp structure which are the outgrowths from epidermal cells of stem or leaf. It helps the plant in scrambling over other plants. It is also protective against herbivory. Example: Rosa spp.

IV. Storage Leaves

Some plants of saline and xerophytic habitats and members of the family Crassulaceae commonly have fleshy or swollen leaves. These succulent leaves store water, mucilage or food material. Such storage leaves resist desiccation. Example: Aloe, Agave, Bryophyllum.

V. Phyllode

Phyllodes are flat, green-coloured leaflike modifications of petioles or rachis. The leaflets or lamina of the leaf are highly reduced or caducous. The phyllodes perform photosynthesis and other functions of leaf. Example: Acacia auriculiformis (Australian Acacia), Parkinsonia.

VI. Pitcher

The leaf becomes modified into a pitcher in Nepenthes and Sarracenia. In Nepenthes the basal part of the leaf is laminar and the midrib continues as a coiled tendrillar structure. The apical part of the leaf is modified into a pitcher the mouth of the pitcher is closed by a lid which is the modification of leaf apex.

VII. Bladder

In bladderwort (Utricularia), a rootless freefloating or slightly submerged plant common in many water bodies, the leaf is very much segmented. Some of these segments are modified to form bladder-like structures, with a trap-door entrance that traps aquatic animalcules.

VIII. Floral Leaves

Floral parts such as sepals, petals, stamens and carpels are modified leaves. Sepals and petals are leafy. They are protective in function and considered non-essential reproductive parts. Petals are usually coloured which attract the insects for pollination. Stamens are considered pollen bearing microsporophylls and carpels are ovule bearing megasporophylls.

Leaf Duration
Leaves may stay and function for few days to many years, largely determined by the adaptations to climatic conditions.

Caducuous (Fagacious)
Falling off soon after formation. Example: Opuntia, Cissus quadrangularis.

Deciduous
Falling at the end of growing season so that the plant (tree or shrub) is leafless in winter/summer season. Example: Maple, Plumeria, Launea, Erythrina.

Evergreen
Leaves persist throughout the year, falling regularly so that tree is never leafless. Example: Mimusops, Calophyllum.

Marcescent
Leaves not falling but withering on the plant as in several members of Fagaceae.

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Shoot System Characteristic Features and its Various Types

The plumule of the embryo of a germinating seed grows into stem. The epicotyl elongates after embryo growth into the axis (the stem) that bears leaves from its tip, which contain the actively dividing cells of the shoot called apical meristem.

Further cell divisions and growth result in the formation of mass of tissue called a leaf primordium. The point from which the leaf arises is called node. The region between two adjacent nodes is called internode.

I. Characteristic Features of the Stem

1. The stem is aerial, green, photosynthetic and has nodes and internodes.
2. It is positively phototropic and negatively geotropic.
3. It has nodes and internodes.
4. Stem bears vegetative bud for vegetative growth of the plant, and floral buds for reproduction, and ends in a terminal bud.
5. The young stem is green and thus carries out photosynthesis
6. During reproductive growth stem bears flowers and fruits.
7. Branches arise exogenously
8. Some stems bears multicellular hairs of different kinds.

II. Functions of the Stem

Primary Functions

1. It provides support and bears leaves, flowers and fruits.
2. It transports water and mineral nutrients to other parts from the root.
3. It transports food prepared by leaves to other parts of the plant body.

Secondary Functions

1. Food Storage:
Example: Solanum tuberosum, Colocasia and Zingiber officinale

2. Perennation / Reproduction:
Example: Zingiber officinale, Curcuma longa

3. Water Storage:
Example: Opuntia

4. Bouyancy:
Example: Neptunia

5. Photosynthesis:
Example: Opuntia, Ruscus, Euphorbia.

6. Protection:
Example: Citrus, Bougainvillea, Acacia.

7. Support:
Example: Passiflora, Vitis, Cissus quadrangularis.

Buds

Buds are the growing points surrounded by protective scale leaves. The bud primordium matures into bud. They have compressed axis in which the internodes are not elongated and the young leaves are closed and crowded.

When these buds develop, the internodes elongate and the leaves spread out. Buds have architecture identical to the original shoot and develop into lateral branches or may terminate by developing into a flower or inflorescence.

Based on origin, buds are classified into:-

• Terminal or Apical bud
• Lateral or Axillary or Axil bud based on function buds are classified into

(a) Vegetative bud
(b) Floral or Reproductive bud.

1. Terminal Bud or Apical Bud:
These buds are present at the apex of the main stem and at the tips of the branches.

2. Lateral Bud or Axillary Bud:
These buds occur in the axil of the leaves and develop into a branch or flower.

3. Extra Axillary Bud:
These buds are formed at nodes but outside the axil of the leaf as in Solanum americanum.

4. Accessory Bud:
An extra bud on either side (collateral bud) or above (superposed bud or serial bud) the axillary bud. Example: Citrus and Duranta.

5. Adventitious Buds:
Buds arising at any part other than stem are known as adventitious buds. Radical buds are those that arises from the lateral roots which grow into plantlets. Example: Millingtonia, Bergera koenigii (Murraya koenigii), Coffa arabica and Aegle marmelos. Foliar buds are those that grow on leaves from veins or from margins of the leaves.

Example: Begonia (Elephant ear plant) and Bryophyllum (Sprout leaf plant). Cauline buds arise directly from the stem either from cut, pruned ends or from branches. Adventitious buds function as propagules which are produced on the stem as tuberous structures. Example: Dioscorea, Agave.

6. Bulbils (or specialized buds):
Bulbils are modified and enlarged bud, meant for propagation. When bulbils detach from parent plant and fall on the ground, they germinate into new plants and serve as a means of vegetative propagation. Example: Agave and Allium proliferum.

Types of Stem

Majority of angiosperm possess upright, vertically growing erect stem. They may be many types they are:-

1. Excurrent
2. Decurrent
3. Caudex and
4. Culm

1. Excurrent

The main axis shows continuous growth and the lateral branches gradually becoming shorter towards the apex which gives a conical appearance to the trees. Example: Monoon longifolium (Polyalthia longifolia), Casuarina.

2. Decurrent

The growth of lateral branch is more vigorous than that of main axis. The tree has a rounded or spreading appearance. Example: Mangifera indica.

3. Caudex

It is an unbranched, stout, cylindrical stem, marked with scars of fallen leaves. Example: Cocos nucifera.

4. Culm

Erect stems with distinct nodes and usually hollow internodes clasped by leaf sheaths. Example: Majority of grasses including Bamboo.

Modification of Stem

I. Aerial Modification of Stem

1. Creepers

These are plants growing closer (horizontally) to the ground and produce roots at each node. Example: Cynodon dactylon, Centella.

2. Trailers (Stragglers)

It is a weak stem that spreads over the surface of the ground without rooting at nodes. They are divided into 3 types,

(i) Prostrate (Procumbent):
A stem that grows flat on the ground. Example: Indigofera prostrata.

(ii) Decumbent:
A stem that grows flat but becomes erect during reproductive stage. Example: Tridax.

(iii) Diffuse:
A trailing stem with spreading branches. Example: Boerhavia diffusa.

3. Climbers

These plants have long weak stem and produce special organs for attachment for climbing over a support. Climbing helps to display the leaves towards sunlight and to position the flower for effective pollination.

(i) Root Climbers

Plants climbing with the help of adventitious roots (arising from nodes) as in species of Piper betel, Piper nigrum, Pothos.

(ii) Stem Climbers (Twiners)

These climbers lack specialised structure for climbing and the stem itself coils around the support. Example: Ipomoea, Clitoria, Quisqualis.

Stem climbers may coil around the support either clockwise or anti-clockwise. Clockwise coiling climbers are called dextrose. Example: Dioscorea alata. Anti-clockwise coiling climbers are called sinistrose. Example: Dioscorea bulbifera.

(iii) Hook Climbers

These plants produce specialized hook like structures which are the modification of various organs of the plant. In Artabotrys inflorescence axis is modified into hook. In Calamus (curved hook) leaf tip is modified into hook. In Bignonia unguis-cati the leaflets are modified into curved hook (figure: 3.17). In Hugonia the axillary buds modified into hook.

(iv) Thorn Climbers

Climbing or reclining on the support with the help of thorns as in Bougainvillea and Carissa.

(v) Lianas (woody Stem Climber)

Woody perennial climbers found in tropical forests are lianas. They twine themselves around tall trees to get light. Example: Hiptage benghalensis, Bauhinia vahlii.

(vi) Tendril Climbers

Tendrils are thread-like coiling structures which help the plants in climbing. Tendrils may be modifications of Stem – as in Vitis and Cissus quadrangularis; Inflorescence axis – Antigonon; Leaf – Lathyrus; Leaflets – Pisum sativum; Petiole – Clematis; Leaftip – Gloriosa; Stipules – Smilax. In pitcher plant (Nepenthes) the midrib of the leaf often coils around a support like a tendril and holds the pitcher in a vertical position.

4. Phylloclade

This is a green, flattened cylindrical or angled stem or branch of unlimited growth, consisting of a series of nodes and internodes at long or short intervals. Phylloclade is characteristic adaptation of xerophytes where the leaves often fall off early and modified into spines or scales to reduce transpiration.

The phylloclade takes over all the functions of leaves, particularly photosynthesis. The phylloclade is also called as cladophyll. Example: Opuntia, Phyllocactus, Muehlenbeckia (flattened phylloclade) Casuarina, Euphorbia tirucalli, Euphorbia antiquorum (cylindrical phylloclade).

5. Cladode

Cladode is a flattened or cylindrical stem similar to Phylloclade but with one or two internodes only. Their stem nature is evident by the fact that they bear buds, scales and flowers. Example: Asparagus (cylindrical cladode), Ruscus (flattened cladode).

6. Thorns

Thorn is a woody and sharp pointed modified stem. Either the axillary bud or the terminal bud gets modified into thorns. In Citrus and Atalantia axillary bud is modified into thorns.

II. Sub Aerial Stem Modifications

Sub aerial stem found in plants with weak stem in which branches lie horizontally on the ground. These are meant for vegetative propagation. They may be sub aerial or partially sub terranean.

1. Runner
This is a slender, prostrate branch creeping on the ground and rooting at the nodes. Example: Oxalis (Wood sorrel), lawn grass (Cynodon dactylon).

2. Stolon
This is also a slender, lateral branch originating from the base of the stem. But it first grows obliquely above the ground, produces a loop and bends down towards the ground. When touches the ground it produces roots and becomes an independent plantlet. Example: Mentha piperita (peppermint), Fragaria indica (wild strawberry).

3. Sucker
Sucker develops from an underground stem and grows obliquely upwards and gives rise to a separate plantlet or new plant. Example: Chrysanthemum, Bambusa.

4. Offset
Offset is similar to runner but found in aquatic plants especially in rosette leaved forms. A short thick lateral branch arises from the lower axil and grows horizontally leafless for a short distance, then it produces a bunch of rosette leaves and root at nodes. Example: Eichhornia (water hyacinth), Pistia (water lettuce).

III. Underground Stem Modifications

Perennial and some biennial herbs have underground stems, which are generally known as root stocks. Rootstock functions as a storage and protective organ. It remains alive below the ground during unfavourable conditions and resumes growth during the favourable conditions.

Underground stems are not roots because they possess nodes, internodes, scale-leaves and buds. Rootstock also lack root cap and root hairs but they possess terminal bud which is a characteristics of stem.

1. Bulb
It is a condensed conical or convex stem surrounded by flshy scale leaves. They are of two types:-

1. Tunicated (Coated) Bulb:
In which the stem is much condensed and surrounded by several concentric layers of scale leaves. The inner scales commonly flshy, the outer ones dry. They can be classifid into two types (a) Simple Tunicated bulb Example: Allium cepa (b) Compound Tunicated bulb. Example: Allium sativum.

2. Corm
This is a succulent underground stem with an erect growing tip. The corm is surrounded by scale leaves and exhibit nodes and internodes. Example: Amorphophallus, Colocasia, Colchicum.

3. Rhizome
This is an underground stem growing horizontally with several lateral growing tips. Rhizome posses conspicuous nodes and internodes covered by scale leaves. Example: Zingiber officinale, Canna, Curcuma longa, Musa.

4. Tuber
This is a succulent underground spherical or globose stem with many embedded axillary buds called “eyes”. Example: Solanum tuberosum, Helianthus tuberosus.

IV. Stem Branching

Branching pattern is determined by the relative activity of apical meristems. The mode of arrangement of branches on a stem is known as branching. There are two main types of branching,

• Lateral branching and
• Dichotomous branching. Based on growth pattern stems may show indeterminate or determinate growth.

1. Indeterminate:
The terminal bud grows uninterrupted and produce several lateral branches. This type of growth is also known as monopodial branching. Example: Polyalthia, Swietenia.

2. Determinate:
The terminal bud caese to grow after a period of growth and the further growth is taken care by successive or several lateral meristem or buds. This type of growth is also known as sympodial branching. Example: Cycas.

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Root System Types and its Characteristic Features

The root is non-green, cylindrical descending axis of the plant that usually grows into the soil (positively geotropic). It develops from the radicle which is the first structure that comes out when a seed is placed in the soil. Root is responsible for absorption of water and nutrients and anchoring the plant.

I. Characteristic Features

• Root is the descending portion of the plant axis.
• Generally non-green in colour as it lacks chlorophyll.
• Does not possess nodes, internodes and buds (Exception in sweet potato and members of Rutaceae, roots bear buds which help in vegetative propagation)
• It bears root hairs (To absorb water and minerals from the soil)
• It is positively geotropic and negatively phototropic in nature.

II. Regions of Root

Root tip is covered by a dome shaped structure made of parenchymatous cells called root cap.

It protects the meristematic cells in the apex. In Pandanus multiple root cap is present. In Pistia instead of root cap, root pocket is present. A few millimeters above the root cap the following three distinct zones have been classified based on their meristematic activity.

• Meristematic Zone
• Zone of Elongation
• Zone of Maturation

Types of Root System

I. Tap Root System

Primary root is the direct prolongation of the radicle. When the primary root persists and continues to grow as in dicotyledons, it forms the main root of the plant and is called the Tap root. Tap root produces lateral roots that further branches into finer roots. Lateral roots along with the branches together called as secondary roots.

II. Adventitious Root System

Root developing from any part of the plant other than radicle is called adventitious root. It may develop from the base of the stem or nodes or internodes. Example: Monstera deliciosa, Piper nigrum. In most of the monocots the primary root of the seedling is short lived and lateral roots arise from various regions of the plant body. These are bunch of thread-like roots nearly equal in size which are collectively called fibrous root system generally found in grasses. Example: Oryza sativa, Eleusine coracana.

Functions of Root

Root performs two kinds of functions namely primary and secondary functions.

Primary Function

• Absorb water and minerals from soil.
• Help to anchor the plant firmly in the soil.

Secondary Function

In some plants roots perform additional functions. These are called secondary functions. To perform additional functions, structure of roots are modified.

Modifications of Root

I. Tap Root Modification

a. Storage Roots

1. Conical Root:
These are cone like, broad at the base and gradually tapering towards the apex. Example: Daucus carota.

2. Fusiform Root:
These roots are swollen in the middle and tapering towards both ends. Example: Raphanus sativus

3. Napiform Root:
It is very broad at the apex and suddenly tapers like a tail at the base. Example: Beta vulgaris

b. Breathing Root

Some mangrove plants like Avicennia, Rhizophora, Bruguiera develop special kinds of roots (Negatively geotropic) for respiration because the soil becomes saturated with water and aeration is very poor. They have a number of breathing pores on pneumatophores for exchange of gases.

II. Adventitious Root Modification

a. Storage Roots

1. Tuberous Root:
These roots are swollen without any definite shape. Tuberous roots are produced singly and not in clusters. Example: Ipomoea batatas.

2. Fasciculated Root:
These roots are in cluster from the base of the stem Example: Dahlia, Asparagus.

3. Nodulose Root:
In this type of roots, swelling occurs only near the tips. Example: Maranta (Arrow root) Curcuma amada (Mango ginger), Curcuma longa (Turmeric)

4. Moniliform or Beaded Root:
These roots swell at frequent intervals giving them a beaded appearance. Example: Vitis, Portulaca, Momordica.

5. Annulated Root:
These roots have a series of ring – like swelling on their surface at regular intervals. Example: Psychotria (Ipecac)

b. Mechanical Support

1. Prop (Pillar) Root

These roots grow vertically downward from the lateral branches into the soil. Example: Ficus benghalensis (banyan tree), Indian rubber.

2. Stilt (Brace) Root

These are thick roots growing obliquely from the basal nodes of the main stem. These provide mechanical support. Example: Saccharum officinarum, Zea mays, Pandanus and Rhizophora.

3. Climbing (clinging) Roots

These roots are produced from the nodes of the stem which attach themselves to the support and help in climbing. To ensure a foothold on the support they secrete a sticky juice which dries up in air, attaching the roots to the support. Example: Piper betel.

4. Buttress Root

In certain trees broad plank like outgrowths develop towards the base all around the trunk. They grow obliquely downwards and give support to huge trunks of trees. This is an adaptation for tall rain forest trees. Example: Bombax ceiba (Red silk cotton tree), Ceiba pentandra (whitesilkcottontree), Delonix regia, Bombax.

c. Vital Functions

1. Epiphytic or Velamen Root

Some epiphytic orchids develop a special kind of aerial roots which hang freely in the air. These roots develop a spongy tissue called velamen which helps in absorption of moisture from the surrounding air. Example: Vanda, Dendrobium.

2. Foliar Root

Roots are produced from the veins or lamina of the leaf for the formation of new plant. Example: Bryophyllum, Begonia.

3. Sucking or Haustorial Roots

These roots are found in parasitic plants. Parasites develop adventitious roots from stem which penetrate into the tissue of host plant and suck nutrients. Example: Cuscuta (dodder), Cassytha, Orobanche (broomrape), Viscum (mistletoe), Dendrophthoe.

4. Photosynthetic or Assimilatory Roots

Roots of some climbing or epiphytic plants develop chlorophyll and turn green which help in photosynthesis. Example: Tinospora, Trapa natans (water chestnut), Taeniophyllum.