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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.

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Parts of a Flowering Plant

Flowering plants are called “Angiosperms” or Magnoliophytes. They are sporophytes consisting of an axis with an underground “Root system” and an aerial “Shoot System”. The shoot system has a stem, branches and leaves. The root system consists of root and its lateral branches.

There are four main flower parts in angiosperms: sepals, petals, stamens, and carpels.

A typical flower has four main parts or whorls known as the calyx, corolla, androecium, and gynoecium (Figure 1). The outermost whorl of the flower has green, leafy structures known as sepals. The sepals, collectively called the calyx, help to protect the unopened bud.

Most flowers have four main parts: sepals, petals, stamens, and carpels. The stamens are the male part whereas the carpels are the female part of the flower. Most flowers are hermaphrodite where they contain both male and female parts.

Stamen. The male parts of a flower consist of an elongated cluster of sacs, called an anther, which emerges atop a thin filament when the flower opens.

• Stigma
• Calyx
• Pistil
• Colas
• More Hydro

Insights

Plant Parts:
Root, Stem, Leaf, Transpiration, Respiration in Plants, Flower, Androecium, Gynoecium, Fruit, Transport Of Water And Minerals In Plants.

Angiosperms:
Flowering plants that have a condensed shoot tip specialized for reproduction.

Anthers:
The bright yellow sacs that produce and contain the pollen grains.

• Composites
• Filament
• Gametes
• Gymnosperms
• Nectar
• Nectaries

The important parts of a flower include:

• Sepals
• Petals
• Stamens
• Pistil

Parts of a Flower

Petal:
The petals of a flower often attract insects or other animals.

Ovary:
The ovary is the part of the carpel (female parts of the flower) that produces seeds.

Stamen:
The male part of this flower is made up of six identical stamens.

• Carpel
• Stigma
• Sepal

The pistil is a plant’s female part. It generally is shaped like a bowling pin and is located in the flower’s center. It consists of a stigma, style and ovary. The stigma is located at the top and is connected by the style to the ovary.

Style:
This is the name for the stalk of the pistil. When pollen reaches the stigma, it begins to grow a tube through the style called a pollen tube, which will eventually reach the ovary. The style therefore acts as a buffer against pollen contamination, since only compatible pollen is able to grow a pollen tube.

The primary purpose of a flower is reproduction. Since the flowers are the reproductive organs of plant, they mediate the joining of the sperm, contained within pollen, to the ovules – contained in the ovary. Pollination is the movement of pollen from the anthers to the stigma.

Basic parts of most all plants are roots, stems, leaves, flowers, fruits, and seeds. The roots help provide support by anchoring the plant and absorbing water and nutrients needed for growth. They can also store sugars and carbohydrates that the plant uses to carry out other functions.

The three main parts are: the roots, the leaves, and the stem. Each part has a set of jobs to do to keep the plant healthy. The roots absorb water and minerals from the soil and anchor the plant in the ground. The stem supports the plant above ground, and carries the water and minerals to the leaves.

The most beautiful rare flowers in the world include the Franklin tree flower, the Fire Lily, Kadupul flower, and Chocolate Cosmos. Rare flowers can be plants that only bloom under specific conditions or are only rarely found growing in the wild. One of the rarest flowers in the world is the Middlemist Red.

Now I bet you’re wondering how to get your own Animal Crossing: New Horizons Lily of the Valley. These unusual blooms are the rarest of all the Animal Crossing: New Horizons flowers, and actually can’t be grown using traditional means.

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Life Span of Vegetative Morphology and its Various Types

Based on life span plants are classified into 3 types. They are annuals, biennials and perennials

I. Annuals

A plant that completes its life cycle in one growing season. Example: Maize, Water melon, Groundnut, Rice.

II. Biennials

A plant that lives for two seasons, growing vegetatively during the first season and flowering and fruiting during the second season. Example: Carrot, Radish, Cabbage.

III. Perennials

A plant that grows for many years that flowers and set fruits for several seasons during the life span. When they bear fruits every year, they are called polycarpic perennials.

Example: Mango, Sapota. Some plants produce flowers and fruits only once and die after a vegetative growth of several years. These plants are called monocarpic perennials. Example: Bambusa, Agave, Musa.

Vegetative Morphology:
Any portion of a plant that is involved in growth, development, photosynthesis, support, etc., but not involved with sexual reproduction.

All plants die eventually. But according to researchers at the New York Botanical Garden in the Bronx, there is no specific lifespan for plants, except for the plants called “annuals,” which are plants that live for one growing season and then die.

The life span of a plant is the length of time it takes from the beginning of development until death, while the life cycle is the series of stages between the germination of the seed until the plant produces its own seeds.

While the concept of form in biology, opposed to function, dates back to Aristotle (see Aristotle’s biology), the field of morphology was developed by Johann Wolfgang von Goethe (1790) and independently by the German anatomist and physiologist Karl Friedrich Burdach (1800).

The two branches of morphology include the study of the breaking apart (the analytic side) and the reassembling (the synthetic side) of words; to wit, inflectional morphology concerns the breaking apart of words into their parts, such as how suffixes make different verb forms.

In this page you can discover 16 synonyms, antonyms, idiomatic expressions, and related words for morphology, like: morphological, patterning, surface structure, ontogeny, phylogeny, ultrastructural, neuroanatomical, microstructure, geomorphology, plasticity and syllable structure.

The internal structure of words and the segmentation into different kinds of morphemes is essential to the two basic purposes or morphology: the creation of new words and the modification of existing words.

Morphology is the study of the internal structure of words and forms a core part of linguistic study today. The term morphology is Greek and is a makeup of morph- meaning ‘shape, form’, and -ology which means ‘the study of something’.

According to the traditional view, the relation between morphology and syntax is the following: while morphology builds up word forms typically by combining roots with other roots and with affixes, but also by applying other operations to them, syntax takes fully inflected words as input and combines them into phrases.

Morphology:
Study of the rules that govern how morphemes, the minimal meaningful units of language, are used in a language.

Semantics:
The meaning of words and combinations of words in a language. The role of morphology in language acquisition and literacy development across languages. Morphemes are the smallest meaning-bearing units of the language. As such, they are the fundamental building blocks for communication during both language and reading development.

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Plant Habitat and its Various Types

Depending upon where plants grow habitats may be classified into two major categories:

I. Terrestrial and
II. Aquatic

I. Terrestrial

Plants growing on land are called terrestrial plants.

II. Aquatic

Plants that are living in water are called aquatic plants or hydrophytes.

Different Types of Habitat

Forest Habitat:
Forest is a large area covered with plants.

Aquatic Habitat:
Habitat in water is aquatic habitats.

Grassland Habitat:
Grassland is regions dominated by grasses.

Dessert Habitat:
Mountainous and Polar Habitat.

Habitat indicates a specific place where a species or population normally lives in nature, it is a physical area, some particular part of the earth’s surface, air, soil or water.

There are five major biomes found in the world:
Aquatic, Desert, Forest, Grassland, and Tundra.

We will focus on eight habitats:
Polar, Tundra, Evergreen Forests, Seasonal Forests, Grasslands, Deserts, Rainforests, and Oceans. These are global habitats that cover vast areas of the Earth. Of course there are habitats that exist at a smaller scale, like regional, local or micro scale habitats.

Two main types of habitat are water and land. Some animals are more comfortable when they are wet, and others when they are dry!

Examples of Habitats Include:

• Desert
• Meadow
• Woodland
• Grassland
• Forest
• Seashore
• Ocean

The two main types of habitats are terrestrial, or land habitats and aquatic, or water, habitats. Forests, deserts, grasslands, tundra, and mountains are just a few examples of terrestrial habitats.

The area where a particular organism lives naturally is called its habitat. The five major habitats are – forests, grasslands, deserts, mountains and polar regions, and aquatic habitat. Oceans and freshwater together form the aquatic habitat.

The chief environmental factors affecting the habitat of living organisms are temperature, humidity, climate, soil and light intensity.

It’s the entire neighborhood where an animal gets the food, water and cover it needs to survive. Scientists call this home or place its habitat. For humans, habitat may mean the neighborhood or city in which they live.

Different kinds of plants grow naturally in different areas too. Plants and animals will choose where they live mostly because of the water, food and climate of a specific are a habitat is the physical area where the animal or plant lives. An organism’s natural habitat has everything it needs to live.

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Habit and its Various Types of Vegatative Morphology

The general form of a plant is referred as habit. Based on habit, plants are classified into herbs, shrubs, climbers (vines) and trees.

I. Herbs

Herbs are soft stemmed plants with less wood or no wood. Example: Phyllanthus amarus, Cleome viscosa. According to the duration of their life they may be classified as annuals, biennials and perennials. Perennial herbs having a bulb, corm, rhizome or tuber as the underground stem are termed as geophytes. Example: Allium cepa

II. Shrubs

A shrub is a perennial, woody plant with several main stems arising from the ground level. Example: Hibiscus rosa sinensis (shoe flower).

III. Climbers (Vine)

An elongated weak stem generally supported by means of climbing devices are called Climbers (vines) which may be annual or perennial, herbaceous or woody. Liana is a vine that is perennial and woody. Liana’s are major components in the tree canopy layer of some tropical forests. Example: Ventilago, Entada, Bougainvillea.

IV. Trees

A tree is a stout, tall, perennial, woody plant having one main stem called trunk with many lateral branches. Example: Mango, Sapota, Jack, Fig, Teak. If the trunk remains unbranched it is said to be caudex. Example: Palmyra, Coconut.

A habit (or wont as a humorous and formal term) is a routine of behavior that is repeated regularly and tends to occur subconsciously.

The definition of habit is something that you do regularly, or an addiction. Brushing your teeth every morning and every night is an example of a good habit. Being addicted to heroin is an example of having a heroin habit.

Some common synonyms of habit are custom, practice, usage, and wont. While all these words mean “a way of acting fixed through repetition,” habit implies a doing unconsciously and often compulsively.

A hobby is a regular activity that is done for enjoyment. A habit is a regular action or behavior that is acquired through frequent repetition. The key difference between hobby and habit is that a hobby is pursued consciously whereas a habit is often a subconscious act.

Within psychology, the term habit refers to a process whereby contexts prompt action automatically, through activation of mental context-action associations learned through prior performances.

Habits are the things a person does repeatedly until such time that it becomes automatic. While behavior is the reaction of the system on the impulses around it, habit is the thing a person does repeatedly and subconsciously until it becomes a routine. This is the main difference between the two.

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Angiosperms Characteristics and its Silent Features

In the previous section, the characteristic features of one of the spermatophyte called Gymnosperms were discussed. Spermatophytes also include plants bearing ovules enclosed in a protective cover called ovary, such plants are called Angiosperms.

They constitute major plant group of our earth and are adapted to the terrestrial mode of life. This group of plants appeared during the early cretaceous period (140 million years ago) and dominates the vegetation on a global scale. The sporophyte is the dominant phase and gametophyte is highly reduced.

Salient Features of Angiosperms

• Vascular tissue (Xylem and Phloem) is well developed.
• Flowers are produced instead of cone
• The Ovule remains enclosed in the ovary.
• Pollen tube helps in fertilization, so water is not essential for fertilization.
• Double fertilization is present. The endosperm is triploid.
• Angiosperms are broadly classified into two classes namely Dicotyledons and Monocotyledons.

Characteristic Features of Dicotyledons and Monocotyledons

Dicotyledons

Morphological Features

Reticulate venation is present in the leaves. Presence of two cotyledons in the seed. Primary root radicle persists as tap root. Flowers tetramerous or pentamerous. Tricolpate (3 furrow) pollen is present.

Anatomical Features

• Vascular bundles are arranged in the form of a ring in stem.
• Vascular bundles are open (Cambium present).
• Secondary growth is present.

Monocotyledons

Morphological features Parallel venation is present in the leaves. Presence of single cotyledon in the seed. Radicle doesn’t persist and fibrous root is present. Flowers trimerous. Monocolpate (1 furrow) Pollen is present.

Anatomical Features

• Vascular bundles are scattered in the stem
• Vascular bundles are closed (Cambium absent).
• Secondary growth is absent.

Current Angiosperm Phylogeny Group (APG) System of classification doesn’t recognize dicots as a monophyletic group. Plants that are traditionally classified under dicots are dispersed in several clades such as early Magnolids and Eudicots.

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Pteridophytes Types and its General Characteristic Features

Seedless Vascular Cryptogams

From the previous section, we are aware of the salient features of amphibious plants called bryophytes. But there is a plant group called pteridophytes which are considered as first true land plants. Further, they were the first plants to acquire vascular tissue namely xylem and phloem, hence called vascular cryptogams. Club moss, horsetails, quill worts, water ferns and tree ferns belong to this group. This chapter deals with the characteristic features of Pteridophytes.

Pteridophytes are the vascular cryptogams and were abundant in the Devonian period of Palaeozoic era (400 million years ago). These plants are mostly small, herbaceous and grow well in moist, cool and shady places where water is available. The photographs for some pteridophytes are given in Figure 2.6.

General Characteristic Features of Pteridophytes:

1. Plant body is sporophyte (2n) and it is the dominant phase. It is differentiated into root, stem and leaves.
2. Roots are adventitious.
3. Stem shows monopodial or dichotomous branching.
4. Leaves may be microphyllous or megaphyllous.
5. Stele is protostele but in some forms siphonostele is present (Marsilea)
6. Tracheids are the major water conducting elements but in Selaginella vessels are found.
7. Sporangia, spore bearing bag like structures are borne on special leaves called sporophyll. The Sporophylls get organized to form cone or strobilus. Example: Selaginella, Equisetum.
8. They may be homosporous (produce one type of spores-Lycopodium) or Heterosporous (produce two types of spores-Selaginella). Heterospory is the origin for seed habit.
9. Development of sporangia may be eusporangiate (development of sporangium from group of initials) or leptosporangiate (development of sporangium from single initial).
10. Spore mother cells undergo meiosis and produce spores (n).
11. Spore germinates to produce haploid, multicellular green, cordate shaped independent gametophytes called prothallus.
12. Fragmentation, resting buds, root tubers and adventitious buds help in vegetative reproduction.
13. Sexual reproduction is oogamous. Sex organs, namely antheridium and archegonium are produced on the prothallus.
14. Antheridium produces spirally coiled and multiflagellate antherozoids.
15. Archegonium is flask shaped with broad venter and elongated narrow neck. The venter possesses egg or ovum and neck contain neck canal cells.
16. Water is essential for fertilization. After fertilization a diploid zygote is formed and undergoes mitotic division to form embryo.
17. Pteridophytes show apogamy and apospory.

Reimer (1954) proposed a classification for pteridophytes. In this classification, the pteridophytes are divided into five subdivisions.

• Psilophytopsida
• Psilotopsida
• Lycopsida
• Sphenopsida
• Pteropsida.

There are 19 orders and 48 families in the classification.

Economic Importance

The Economic importance of Pteridophyte is given in Table 2.3

Types of Stele

The term stele refers to the central cylinder of vascular tissues consisting of xylem, phloem, pericycle and sometimes medullary rays with pith (Figure 2.7).

There are two types of steles

1. Protostele
2. Siphonostele

1. Protostele:

In protostele phloem surrounds xylem. The type includes Haplostele, Actinostele, Plectostele, and Mixed protostele.

(i) Haplostele:
Xylem surrounded by phloem is known as haplostele. Example: Selaginella.

(ii) Actinostele:
Star shaped xylem core is surrounded by phloem is known as actinostele. Example: Lycopodium serratum.

(iii) Plectostele:
Xylem plates alternates with phloem plates. Example: Lycopodium clavatum.

(iv) Mixed prototostele:
Xylem groups uniformly scattered in the phloem. Example: Lycopodium cernuum.

2. Siphonostele:

In siphonostele xylem is surrounded by phloem with pith at the centre. It includes Ectophloic siphonostele, Amphiphloic siphonostele, Solenostele, Eustele, Atactostele and Polycylic stele.

(i) Ectophloic Siphonostele:

The phloem is restricted only on the external side of the xylem. Pith is in centre. Example: Osmunda.

(ii) Amphiphloic Siphonostele:

The phloem is present on both the sides of xylem. The pith is in the centre. Example: Marsilea.

(iii) Solenostele:

The stele is perforated at a place or places corresponding the origin of the leaf trace.

(a) Ectophloic Solenostele:
Pith is in the centre and the xylem is surrounded by phloem Example Osmunda.

(b) Amphiphloic solenostele:
Pith is in the centre and the phloem is present on both sides of the xylem. Example: Adiantum pedatum.

(c) Dictyostele:
The stele is separated into several vascular strands and each one is called meristele. Example: Adiantum capillus-veneris.

(iv) Eustele:

The stele is split into distinct collateral vascular bundles around the pith. Example: Dicot stem.

(v) Atactostele:

The stele is split into distinct collateral vascular bundles and are scattered in the ground tissue. Example: Monocot stem.

(vi) Polycyclicstele:

The vascular tissues are present in the form of two or more concentric cylinders. Example: Pteridium.

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Bryophytes Definition and its Economic Importance

Amphibians of Plant Kingdom

In the previous chapter, we noticed a wide range of thallus organization in Algae. Majority of them are aquatic. The development of heterotrichous habit, development of parenchyma tissue and dichotomous branching in some algae supports the view that colonization of plants in land occurred in the past.

Bryophytes are simplest and most primitive plant groups descended from alga – like ancestors. They are simple embryophytes. Let us learn about the structure and reproduction of these primitive land plants called Bryophytes in detail.

Bryophytes are simplest land inhabiting cryptogams and are restricted to moist, shady habitats. They lack vascular tissue and hence called ‘Non- vascular cryptogams’. They are also called as ‘amphibians of plant kingdom’ because they need water for completing their life cycle.

General Characteristic Features

• The plant body of bryophyte is gametophyte and is not differentiated into root, stem and leaf like structure.
• Most of them are primitive land dwellers. Some of them are aquatic (Riella, Ricciocarpus).
• The gametophyte is conspicuous, long lived phase of the life cycle. Thalloid forms are present in liverworts and Hornworts.

In Mosses leaf like, stem like structures are present. In Liverworts thallus grows prostrate on the ground and is attached to the substratum by means of rhizoids. Two types of rhizoids are present namely smooth walled and pegged or tuberculate.

Multicellular scales are also present. In Moss the plant body is erect with central axis bearing leaf like expansions. Multicellular rhizoids are present. The structure and reproduction in Bryophytes is given in Figure 2.5.

Vascular tissue like xylem and phloem are completely absent, hence called ‘Non vascular cryptogams’. Vegetative reproduction takes place by the formation of adventitious buds (Riccia fluitans) tubers develop in Anthoceros.

In some forms small detachable branches or brood bodies are formed, they help in vegetative reproduction as in Bryopteris fruticulosa. In Marchantia propagative organs called gemmae are formed and help in reproduction. Sexual reproduction is oogamous. Antheridia and Archegonia are produced in a protective covering and are multicellular.

The antheridia produces biflagellate antherozoids which swims in thin film of water and reach the archegonium and fuse with the egg to form diploid zygote.

Water is Essential for Fertilization

The zygote is the first cell of the sporophyte generation. It undergoes mitotic division to form multicellular undifferentiated embryo. The embryogeny is exoscopic (the first division of the zygote is transverse and the apex of the embryo develops from the outer cell). The embryo divides and give rise to sporophyte.

The sporophyte is dependent on gametophyte. It is differentiated into three recognizable parts namely foot, seta and capsule.

Foot is the basal portion and is embedded in the gametophyte through which water and nutrients are supplied for the sporophyte. The diploid spore mother cells found in the capsule region undergoes meiotic division and give rise to haploid spores. Bryophytes are homosporous. In some sporophytes elaters are present and help in dispersal of spores (Example: Marchantia). The spores germinate to produce gametophyte.

The zygote, embryo and the sporogonium constitute sporophytic phase. The green long living haploid phase is called gametophytic phase. The haploid gametophytic phase alternates with diploid sporophyte and shows heterologous alternation of generation. Proskauer in the year 1957 classified Bryophytes into 3 Classes namely:-

(i) Hepaticopsida:-
(Riccia, Marchantia, Porella and Riella)

(ii) Anthocerotopsida:-
(Anthoceros and Dendroceros)

(iii) Bryopsida:-
(Funaria, Polytrichum and Sphagnum).

Economic Importance

Dead thalli of Sphagnum gets accumulated and compressed, hardened to form peat. In northern Europe (Netherlands) peat is used as fuel in commercial scale. Apart from this nitrates, brown dye and tanning materials are derived from peat.

Sphagnum and peat are also used in horticulture as packing material because of their water holding capacity. Marchantia polymorpha is used to cure pulmonary tuberculosis. Sphagnum, Bryum and Polytrichum are used as food. Bryophytes play a major role in soil formation through succession and help in soil conservation.

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Algae Classification and its Importance

Rain brings joy and life to various organisms on earth. Have you noticed some changes in and around you after the rain? Could you identify the reason for the slippery nature of the terrace and green patches on the wall of our home, green colour of puddles and ponds? Why should we clean our water tanks very often? The reason is algae.

Algae are simple plants that lack true roots, true stems and true leaves. Two-third of our earth’s surface is covered by oceans and seas. The photosynthetic plants called algae are present here. More than half of the total primary productivity of the world depends on this plant group. Further, other aquatic organisms also depend upon them for their existence.

Algae are autotrophs, and grow in a wide range of habitats. Majority of them are aquatic, marine (Gracilaria, and Sargassum) and freshwater (Oedogonium, and Ulothrix) and also found in soils (Fritschiella, and Vaucheria). Chlorella lead an endozoic life in hydra and sponges whereas Cladophora crispata grow on the shells of molluscs. Algae are adapted to thrive in harsh environment too.

Dunaliella salina grows in salt pans (Halophytic alga). Algae growing in snow are called Cryophytic algae. Chlamydomonas nivalis grow in snow covered mountains and impart red colour to the snow (Red snow). A few algae grow on the surface of aquatic plants and are called epiphytic algae (Coleochaete, and Rhodymenia). The study of algae is called algology or phycology. Some of the eminent algologists include F.E. Fritsch, F.E. Round, R.E. Lee, M.O. Parthasarathy Iyengar, M.S. Randhawa, Y. Bharadwaja, V.S. Sundaralingam and T.V. Desikachary.

General Characteristic Features

The algae show a great diversity in size, shape and structure. A wide range of thallus organisation is found in algae. Unicellular motile (Chlamydomonas), unicellular non-motile (Chlorella), Colonial motile (Volvox), Colonial non motile (Hydrodictyon), siphonous (Vaucheria), unbranched filamentous (Spirogyra), branched filamentous (Cladophora), discoid (Coleochaete) heterotrichous (Fritschiella), Foliaceous (Ulva) to giant kelps (Laminaria and Macrocystis). The thallus organization in algae is given in Figure 2.3.

Algae are eukaryotes except blue green algae. The plant body does not show differentiation into tissue systems. The cell wall of algae is made up of cellulose and hemicellulose. Siliceous walls are present in diatoms. In Chara the thallus is encrusted with calcium carbonate.

Some algae possess algin, polysulphate esters of polysaccharides which are the sources for the alginate, agar agar and carrageenan. The cell has a membrane bound nucleus and cell organelles like chloroplast, mitochondria, endoplasmic reticulum, golgi bodies etc., Pyrenoids are present. They are proteinaceous bodies found in chromatophores and assist in the synthesis and storage of starch.

The pigmentation, reserve food material and flagellation differ among the algal groups. Algae reproduces by vegetative, asexual and sexual methods (Figure 2.4).

Vegetative reproduction includes fission (In unicellular forms the cell divides mitotically to produce two daughter cells Example: Chlamydomonas); Fragmentation (fragments of parent thallus grow into new individual Example: Ulothrix) budding (A lateral bud is formed in some members like Protosiphon and helps in reproduction) bulbils, (a wedge shaped modified branch develop in Sphacelaria) akinetes (Thick walled spores meant for perennation and germinates with the advent of favourable condition Example: Pithophora) and Tubers (Structures found on the rhizoids and the lower nodes of Chara which store food materials).

Asexual reproduction takes place by the production of zoospores motile spores (Ulothrix, Oedogonium) aplanospore (thin walled non motile spores Example: Vaucheria); autospores (spores which look similar to parent cell Example: Chlorella); hypnospore (thick walled aplanospore – Example: Chlamydomonas nivalis) and Tetraspores (Diploid thallus of Polysiphonia produce haploid spores after meiosis).

Sexual Reproduction in Algae is of Three Types

• Isogamy (Fusion of morphologically and Physiologically similar gametes Example: Ulothrix)
• Anisogamy (Fusion of either morphologically or physiologically dissimilar gametes Example: Pandorina)
• Oogamy (Fusion of both morphologically and physiologically dissimilar gametes. Example: Sargassum).

The life cycle shows distinct alternation of generation.

Classification

F.E. Fritsch proposed a classification for algae based on pigmentation, types of flagella, reserve food materials, thallus structure and reproduction. He published his classification in the book “The structure and reproduction of the Algae”(1935). He classified algae into 11 classes namely Chlorophyceae, Xanthophyceae, Chrysophyceae, Bacillariophyceae, Cryptophyceae, Dinophyceae, Chloromonadineae, Euglenophyceae, Phaeophyceae, Rhodophyceae, Cyanophyceae. The salient features of Chlorophyceae, Phaeophyceae and Rhodophyceae are given below.

Chlorophyceae

The members are commonly called ‘Green algae’. Most of the species are aquatic (Fresh water-Spirogyra, Marine – Ulva). A few are terrestrial (Trentipohlia). Variation among the shape of the chloroplast is found in members of algae. It is cup shaped (Chlamydomonas), discoid (Chara), girdle shaped, (Ulothrix), reticulate (Oedogonium), spiral (Spirogyra), stellate (Zygnema) and plate like (Mougeoutia).

Chlorophyll ‘a’ and Chlorophyll ‘b’ are the major photosynthetic pigments. Storage bodies called pyrenoids are present in the chloroplast and store starch. They also contain proteins. The cell wall is made up of inner layer of cellulose and outer layer of pectin.

Vegetative reproduction takes place by means of fragmentation and asexual reproduction is by the production of zoospores, aplanospores and akinetes. Sexual reproduction is present and may be isogamous, anisogamous or oogamous. Examples for this group of algae includes Chlorella, Chlamydomonas, Volvox, Spirogyra, Ulothrix, Chara and Ulva.

Phaeophyceae

The members of this class are called ‘Brown algae’. Majority of the forms are found in marine habitats. Pleurocladia is a fresh water form. The thallus is filamentous (Ectocarpus) frond like (Dictyota) or may be giant kelps (Laminaria and Macrocystis). The thallus is differentiated into leaf like photosynthetic part called fronds, a stalk like structure called stipe and a holdfast which attach thallus to the substratum.

The Pigments include Chlorophyll a, c, Carotenoids and Xanthophylls. A golden brown pigment called fucoxanthin is present and it gives shades of colour from olive green to brown to the algal members of this group. Mannitol and Laminarin are the reserve food materials.

Motile reproductive structures are present. Two laterally inserted unequal flagella are present. Among these one is whiplash and another is tinsel. Although sexual reproduction ranges from isogamy to oogamy, Most of the forms show oogamous type. Alternation of generation is present (isomorphic, heteromorphic or diplontic). Examples for this group include Sargassum, Laminaria, Fucus and Dictyota.

Rhodophyceae

Members of this group include ‘Red algae’ and are mostly marine. The thallus is multicellular, macroscopic and diverse in form. Porphyridium is the unicellular form. Filamentous (Goniotrichum) ribbon like (Porphyra) are also present.

Corallina and Lithothamnion are heavily impregnated with lime and form coral reefs. Apart from chlorophyll a, r-phycoerythrin and r-phycocyanin are the photosynthetic pigments. Asexual reproduction takes place by means of monospores, neutral spores and tetraspores.

The storage product is floridean starch. Sexual reproduction is oogamous. Male sex organ is spermatangium which produces spermatium. Female sex organ is called carpogonium. The spermatium is carried by the water currents and fuse with egg nucleus to form zygote.

The zygote develops into carpospores. Meiosis occurs during carpospore formation. Alternation of generation is present. Examples for this group of algae include Ceramium, Polysiphonia, Gelidium, Cryptonemia and Gigartina.

Economic Importance

The Economic importance of Algae is given in Table 2.2