Morphology of Flowering Plants

Chapter -2

Morphology of Flowering Plants

Morphology of different parts of flowering plants

The abundance of plants and their size from bacteria to huge trees make it difficult to study their morphological characters. Classification of plants has solved the problem to a great extent. Still it is impossible to define precisely the plant body as made up of certain parts only. Plants exhibit vividness in several respects.

The body of the higher plants phanerogams (spermatophytes) is differentiated into root and the shoot.

A part of the plant body which remains in the soil, grows towards gravity, away from light and also fixes the plant in the soil and supplies water and minerals is known as root and has different structures than that of aerial part. Root bears similar organs like rootlets and have root-caps at their apices.

Root

Root is a downward growth o[ the plant ‹not the soil. It is positively geotropic and hydrotropic. Radicle from the germinating seed grows further into the soil to form the root. It produces similar organs. Root does not have nodes or internodes. Branching of the root arises from the pericyclic tissues. Roots are covered by root caps or root heads.

Stem

The plumule develops to form the stem. Thus, stem is an aerial part of the plant. It consists of axis and the leaves. Stem has got the following characteristics:

1. It is ascending axis of the plant and phototropic in nature.
2. It consists of nodes, internodes and buds.
3. It paves rise to branches, leaves and flowers.
4. Stems may be aerial, sub-aerial and underground.

Depending upon the presence of mechanical tissues, the stems may be weak, herbaceous or woody
1. Weak stems: When the stems are thin and long, they are unable to stand erect, and hence may be one of the following types:

(a) Creepers or Prostate stem: When they grow flat on the ground with or without roots. Examples are grasses, Gohari etc.
(b) Climbers: These are too weak to stand alone. They climb on the support with the help of tendrils, hooks, prickles or roots. For examples: Vitis, piper betel, piper longum.
(c) Tinners: These coil the support and grow further. They are thin and wiry i.e., ipomoea and Phaseolus.

1. Produces leaves and exposes them properly to sunlight for carrying out photosynthesis.
2. Conducts water and minerals from roots to leaves and buds.
3. Foods produced by leaves are transported to non-green parts of the plant.
4. Produces flowers and fruits for pollination and seal dispersal.
5. Depending upon the environment it gets suitably modified to perform special functions like storage of foods, means of propagation etc.

Underground Modifications of Stems:

Underground modifications of stems are of the following types:
Rhizome
Tuber
Bulb
Corm.
Rhizome: Grow horizontal under the soil. They are thick and are characterized by the presence of nodes, inter-nodes and scale leaves. They also possess bud in the axil of the scaly leaves. Examples are: Ginger, turmeric, rhubarb, male-fern etc.
Tuber: Tubers are characterized by the presence of 'eyes' from the vegetative buds which grow further and develop into a new plant. Tubers are the swollen underground structure of the plant. The examples of tubers are Potato, Jalap, Aconite etc.
Bulb: In this case, the food material is stored in fleshy scales which overlap the stem. They are present in the axils of the scales and lew of them develop into new plant in the spring season at the expense of stored food material in the bulb. Adventitious roots are present at the base of the bulb. The reserve food material formed by the leaves is stored at their bases and the new bulbs are produced next year. Examples are Garlic, Squill, Onion and Gloriosa.Inflorescence
Plant hear flowers either solitary or in groups. The flowers which are large and showy are normally borne solitary, but which are not so prominent and are small, occur in group or bunches.
Depending upon the type of branching various forms of inflorescences are known. The axis on which the flowers are arranged is known as peduncle while the stalks of flowers are known as pedicels

Flower

The flower is actually a modified shoot meant for production of seeds:

It consists of four different circles (whorls) arranged in a definite manner. A flower is built-up on stem or pedicel with the enlarged end known as thalamus or receptacle. The four whorls of the flowers can be described as under:

Calyx: It is the outermost whorl of flower and is generally green in color, the individual member of which is called sepal.

Corolla: It is the second whorl of flower and is either white or bright colored, each member of which is known as petal.

Androecium: It is the third circle of flower and constitutes the male part. The individual component is called stamen and each stamen consists of filament, anther and connective.

Gynoecium: This is the fourth circle of the flower and constitutes the female part. Each component is known as carpel or pistic/ and is made of stigma, style and ovary.

When all the four whorls are present in a single flower, it is described to be a complete flower, absence of any one of them describes it as incomplete flower. A flower is described to be hermaphrodite or bisexual when it contains stamens and carpels. Absence of any one of them describes it as unisexual flower. When calyx and corolla in a flower are similar in color and shape then both of them (calyx and corolla) together are called Perianth i.e. garlic, onion, asparagus.

Types of Flowers:

When a flower is divided into two equal parts by any vertical section passing through the Centre, then it is described as regs/or symmetrical or actinomorphic flower as in ipomoea, rose, datura and shoe-[lower. But when it cannot be divided equally into two parts by one vertical section then it is described as Urrego/or or asymmetrical or zygomorphic [lower.

When the stamens arise from petals instead of thalamus, the petals are called epipetalous. When the stamens get united with gynoecium the structure is known as gynostemia. The union of stamens among themselves is known as cohesion. When the filaments of stamen get united to form a single bundle it is known as Monadelphous. When it forms two bundles it is known as diadelphous. When anthers get united to form a column (but filaments are free) the stamens are known as syngenesious

When ovary consists of only one carpel it is said to be monocarpellary and when it contains more than one carpel it is said to be polycarpellary. When the carpels in ovary are free, the ovary is described as apocarpous and when they are united it is known as syncarpous.

Arrangement of Floral Parts on Thalamus:

Depending upon the arrangement of floral parts on thalamus, the flowers may be of three types.

Hypogynous flower (Superior ovary): Herein the thalamus is conical, flat, convex and stamens, sepals and petals are arranged at base and ovary at the apex. Examples: Brinjal, China rose, mustard etc.

Epigynous flowers (Half-superior Ovary): Thalamus is flat, sepals and stamens grow around the ovary. The flowers are said to be epigynous as in Rose, Strawberry peach.

Epigynous flower (Inferior-ovary): The thalamus is fused with ovary wall, calyx, corolla, stamen appear at the top and the gynoecium at the bottom as in Sunflower, cucumber, apple etc.

Leaf

The apex of the leaf may be one of the following kinds

Obtuse: Rounded tip i.e. Banyan.

Acute: When it is pointed to form acute ample, but not stiff i.e. Hibiscus.

Acuminate: Pointed tip with much elongation, Pee pal

Recurved: When the apex is curved backward

Cuspidate: With spiny tip like Date palm.

Mucronate: Rounded apex ending abruptly in a short point i.e. vinca, ixora.

Retune: Broad tip with slight notch i.e. Pistoia.

Emarginate: When tip is deeply notched as in Bambina

Tendrillar: Tip forming a tendril such as Gloriosa - superba

Venation:

The arrangements of Yenis in the lamina or leaf-blade is known as venation.

Veins are nothing but vascular bundles. Water and minerals absorbed by roots is conveyed to various parts of leaf by veins and the food synthesized by leaf by way of photosynthesis is translocated to other parts of plant through veins only. Veins also offer strength, support and shape to the lamina of the leaf. The prominent vein in the center of the leaf is known as mid-rib.

In the flowering plants two types of venations exist: 1. Reticulate, 2. Parallel.

Reticulate venation: This type of venation is characterized by the fact that many veins and veinlets in the lamina of the leaf are arranged in the form of network or reticular. This type of venation is characteristic to dicotyledonous leaves. It is further sub-classified as:

(a)Unicostate reticulate venation: Where the leaf contains only one mid-rib and several veins are given out on both the sides to form the network such as Henna, eucalyptus, papal.

(b)Multistate reticulate venation: In this type, many veins of equal strength arise from the end of the petiole. Each vein further branches to give rise to veinlets that form the network. The veins may be convergent (meeting at the apex) or divergent (diverge towards the marlin) as in castor, carioca and Cucurbita.

2. Parallel venation: In this type, the vein and veinlets in leaf-blade are arranged parallel to one another. It is characteristic to monocotyledonous plants with few exceptions like Dios Corea and Sarsaparilla.

(a) Unicostate parallel venation: Wherein the leaf consists of only one midrib running from apex to the petiole of the leaf. The veinlets and veins arise parallel to one another on each side as in banana and canna.

(b)Multistate parallel venation: In case of multistate parallel venation many number of main veins of equal strength arise from the tip or the petiole and run parallel to each other. It may be convergent as in case of several grasses and bamboo or divergent as in case of [an—palm.

Fruit

Phanerogams are said to be matured when they reach the flowering stage. The ovules of the flowers after fertilization get converted into seeds, whereas the ovary wall develops [urther to [orm the protective covering over the seeds which is known as fruit. In botany, this particular coating is also called pericarp.

Pericarp consists of three different layers, one after the other as under:

1. Epicarp: Epicarp is the outermost coating of the pericarp and may be thin or thick.
2. Mesocarp: A layer in between epicarp and endocarp may be pulpy or made up of spongy parenchymatous tissue.
3. Endocarp: The innermost layer of the pericarp may be thin or thick or even woody.

It is not necessary that the fruits should have seeds. If the ovules do not fertilize, the seedless fruits are formed. Depending upon the number of carpels present in the flowers, and other structures, the fruits fall into the following categories:

1. Simple fruits, 2. Aggregate fruits and 3. Compound fruits.

1. Simple fruits: Formed from the single carpel or from syncarpous gynoecium. Once again depending upon the mesocarp whether it is dry or fleshy, they are classified as dry fruits and fleshy fruits. Dry fruits are further sub-classified into dehiscent and indehiscent fruits.
3. Compound fruits: In this particular case, many more flowers come together and form the fruits. e.g. Figs, Pineapple.
2. Aggregate fruits: These fruits get formed from many carpels or apocarpous gynoecium. e.g. Raspberry.

False fruits: Sometimes it so happens that apart from the ovary and the other floral parts like thalamus, receptacle or calyx grow and form the part of the fruit and such a fruit is known as false fruit or pseudocarp. Following are the few examples of pseudocarp in which other parts of the flower forming important part of the fruits are shown in the bracket.

Strawberry (thalamus)
Cashewnut (peduncle and thalamus)
Apple (thalamus)
Marking nut (peduncle)
Rose (thalamus)

Classification of Fruits:

Seeds

The seed is a fertilized ovule and is a characteristic of Phanerogams.

Parenchymatous body of the ovule is known as nucellus contains embryo sac in which fertilization of pollen cells takes place giving rise to embryo. The seeds are characterised by the presence of three parts known as embryo, endosperm and seed-coat.

Seed coat: lt is the outermost layer of the seeds providing necessary protection to the embryo laying inside the seed.

In case of dicotyledonous seeds normally, it is hard and may contain two layers; the outermost thick layer is known as testa while the inner one which is thin is known as tegumen.

In monocotyledonous seeds, it is thin or even may be fused with the wall of the fruit.General Anatomy of root

Embryo: II is the main part of the seed. lt consists of an aXÏS having apical meristem for plumule, radiale the origin or root and adhered to it are one or two cotyledons, differentiating the plants as monocot or dicot.

Endosperm: It is the nutritive tissue nourishing the embryo. It may be present or may not be present in the seed. Depending upon the presence or absence of the seeds are classified as under:

1. Endospermic or albuminous seeds.

2. Non-endospermic or Ex albuminous seeds.

3. Peri spermic seeds.

Endospermic or albuminous seeds: In this seed, the part of the endosperm remains even upto the germination of seed and is partly absorbed by embryo. Therefore, seeds are known as endospermic seeds as in Colchicum, Sabol, linseed, nix-vomica, strophanthus, she Ot and rice.

Non-endospermic or Ex albuminous seeds: In these seeds during the development of seed the endosperm is fully absorbed by embryo and endosperm and is not represented in the seeds, hence they are known as non-endospermic as in Sunflower, tamarind, cotton and soyabean.

Peri spermic seeds: Herein the nucleus develops to such an extent that it forms a big storage tissue and seeds are found to contain embryo, endosperm, perisperm and seed coat;

e.g., Pepper, cardamom, nutmeg, guinea grains.

Seeds are characterized by the following descriptive terms:

(a) Hilum: This is the point of attachment of seed to its stalk.

(b) Micropyle: It is the minute opening of the tubular structure, wherefrom water is provided for the germination of seeds.

(d) Funicle: It is the stalk of the ovule attaching it to the placenta. Chalza: This is the basal portion of ovule where stalk is attached

Special Features of Seeds:

Sometimes apart from the regular growth of seeds additional growth is visible in the form of appendages which attribute to their special features. They are described as under:

(i) Aril: Succulent growth from hilum covering the entire seeds as in nutmeg (Mace) and

yew Seeds.

(ii) Arillode: Outgrowth originating from micropyle and covering the seeds as in

cardamom.

(iii) Arista (awn): Stiff-bristle-like appendage with many flowering glumes o[grasses and found in strophanthus.

(iv) Caruncle: A warty outgrowth from micropyle i.e. castor, croton, viola moringa.

(v) Hairs: Gossypium and Calotropis are examples of this type of outgrowth.

Functions of Seeds

Seed performs the following functions:

1. Most important function of the seeds is reproduction i.e. it terminates into new plant.

2. Seeds are meant for the spread o[the species.

3. Species and varieties do not come to an end by successive formation of seeds by plant. Thus, seeds are 'means o[perennation'.

4. Seeds are 'means of perpetuation of species'.

Uses of Seeds:

1. Due to high protein and fixed oil contents seeds are the essential part of the food. Sunflower, as[flower, Sesame and groundnuts are used for edible oil, while Soyabean, cottonseed are used for isolation of proteins also.

2. Cotton seeds are used as source of cotton fibres.

3. Guar seeds, Isopoll, psyllium are used for the isolation of mucilage.

Morphology of Flowering Plants

Morphology of Flowering Plants

Morphology of different parts of flowering plants

Root

Stem