Basic principles of Pharmacognosy

BASIC PRINCIPLES OF
PHARMACOGNOSY
Ayana R Kumar

Pharmacognosy
The branch of knowledge concerned with medicinal drugs
obtained from plants or other natural sources
 Pharmacognosy is the study of plants or other natural sources
as a possible source of drugs, defines pharmacognosy as "the
study of the physical, chemical, biochemical and biological
properties of drugs, drug substances or potential drugs or drug
substances of natural origin as well as the search for new drugs
from natural sources
 The word "pharmacognosy" is derived from two Greek words:
pharmakon (drug), and gnosis (knowledge)

Plant cells
 Plant cells are eukaryotic cells with a true nucleus
along with specialized structures called organelles
that carry out certain specific functions,
 The plant cell is rectangular and comparatively larger
than the animal cell.
 Even though plant and animal cells are eukaryotic
and share a few cell organelles, plant cells are quite
distinct when compared to animal cell as they
perform different functions.

Plant tissues
A collection of cells performing a specific
function is called tissue.
Plant tissues can be grouped into plant tissue
systems each performing specialized functions.
 A plant tissue system is defined as a functional
unit, connecting all organs of a plant. Plant
tissue system is also grouped into various
tissues based on their functions.

• Three tissue system excising among the plants
based on the size shape and function.
• Epidermal tissue system
 Epidermis
Periderm
• Ground or fundamental tissue system
Collenchyma
Parenchyma
• Vascular tissue system
Xylem
Phloem

Ground or fundamental tissue system

Functions of plant tissues
• Plant tissues have different functions depending upon
their structure and location
• Help provide mechanical strength to organs.
• They help in providing the elasticity and flexibility to
the organs.
• They help the tissues to bend easily in various parts of a
plant like- leaf, stem, and branches without damaging
the plant
• The xylem and phloem tissues help in transportation of
material throughout the plants
• They divide to produce new cells and help in the
growth of the plants.
• They help in various cellular metabolisms
like photosynthesis, regeneration, respiration, etc.

Conjoint vascular bundles
• This is the type of xylem and phloem present
in the same vascular bundles
1. Collateral; Xylem and phloem present in the
vascular bundle in same radius, same side, in
same vascular bundle.
2. Bicollateral; In this type xylem is in the
middle and phloem and cambium lie on either
sides of the xylem

Leaves
Leaves are flat, thin and green appendages to the
stem.

• Leaf come in different shapes, sizes, and colors, and are generally
dorso-ventrally flattened and thin. They are the main organ
responsible for photosynthesis as they contain chlorophyll.
• Leaves have two main parts: The leaf blade and the Stalk or the
petiole
The leaf blade: It is also called the lamina.
• It’s generally broad and flat.
• It is in this layer that photosynthesis occurs.
• It contains a prominent midrib at the center of the leaf blade which
is the main vein.
• From this midrib arise branches called veins.
• They are of different types depending upon the type of edges, the
pattern of the veins and the number of blades per leaf.

The petiole: It is the stalk-like structure which connects
the leaf blade to the stem.
• The petiole has tiny tubes, that connect the veins on
the leaf blade to the stem.
• Few of these enable water transport to the leaf while
the other carry food away from the leaf to other parts
of the plant.
Some plants also contain another part called stipules.
• These are small flap-like structures that grow at the
base of the petioles.
• They are protective in some plants when they protect
the growing petiole while in others, they fall off once
the petiole starts growing.

Each leaf containing following layers
Epidermis: It is the outermost layer and secretes a waxy substance called the cuticle.
• The cuticle helps retain water inside the leaf cells.
• The epidermis houses the guard cells which regulate the movement of water into
and outside the cell.
• Guard cells do so by controlling the size of the pores also called stomata.
Mesophyll: This forms the middle layer of the leaf.
• It is differentiated into two layers depending on the type of cells found: palisade
and spongy mesophyll layers.
• It is in this layer that the chloroplasts are found. Chloroplasts are cell organelles
that contain chlorophyll which is required for photosynthesis.
• The vascular tissues of the leaf are contained in the irregularly arranged spongy
mesophyll cells.
Vascular Tissue: The vascular tissue is actually found in the veins of the leaf.
• The vascular tissues are composed of xylem and phloem which are responsible for
the transport of water and food.

STOMATA
• Stomata are tiny openings or pores in plant tissue that
allow for gas exchange.
• Stomata are typically found in plant leaves but can also
be found in some stems.
• Specialized cells known as guard cells surround
stomata and function to open and close stomatal pores.
• Stomata allow a plant to take in carbon dioxide, which
is needed for photosynthesis.
• They also help to reduce water loss by closing when
conditions are hot or dry. Stomata look like tiny mouths
which open and close as they assist in transpiration.

Types of stomata
• Stomata can be grouped into different types base on the number
and characteristics of the surrounding subsidiary cells.
Types of stomata include:
• Anomocytic Stomata: Possess irregularly shaped cells, similar to
epidermal cells, that surround each stoma.
• Anisocytic Stomata: Features include an unequal number of
subsidiary cells (three) surrounding each stoma. Two of these cells
are significantly larger than the third.
• Diacytic Stomata: Stomata are surrounded by two subsidiary cells
that are perpendicular to each stoma.
• Paracytic Stomata: Two subsidiary cells are arranged parallel to the
guard cells and stomatal pore.
• Gramineous Stomata: The guard cells are narrow in the middle and
wider at the ends. The subsidiary cells are parallel to the guard cells.

Trichomes
• They are fine outgrowths or appendages
on plants, algae, lichens, and certain protists.
• They are of diverse structure and function.
Examples are hairs, glandular hairs, scales, and
papillae.

• Covering trichomes- Elongated structure with apex, body and
base.
• Glandular trichomes- Structure with globular head and stalk

STEMS
• The main functions of stems are to support and
elevation of leaves, fruits, and flowers.
• Stem arranges leaves in a way that it gets direct
sunlight to perform photosynthesis.
• Xylem and Phloem conduct water across the
plant. Stems stores food, water, and nutrients.
• Cells of a stem, meristems, produce new living
tissues. Underground stem, Aerial stem, and sub
aerial stem are three different types of Stem.
• A stem has many important functions it performs
other than letting you climb a tree. Let us take an
in-depth look at the stem of plants.

Structure of a stem
• The stem divides into nodes and internodes.
• The nodes give rise to the leaves and hold the buds which grow into
branches. The internodes separate two nodes.
• Internally, it contains three basic types of tissues: Dermal tissue,
Ground tissue, and Vascular tissue all of which are made of
simple cells.
• Epidermis: The epidermis is a single layer of cells that make up the
external tissue of the stem called dermal tissue.
• This tissue covers the stem and protects the underlying tissue.
Woody plants have an extra layer of protection on top of the
epidermis known as bark.
• In some cases, the bears’ multi-cellular hairs and a few stomata.
• Ground tissue divides into two- the central portion is known as the
pith and the cortex which lies between the vascular tissue and the
epidermis

The cortex can be further divided into three layers:
Hypodermis: It is the outermost layer of the cortex.
• It is formed of 4 to 5 cell thick layer of collenchymatous cells. These cells
are living and contain chloroplasts.
General cortex: Lies below the hypodermis.
• It consists of thin-walled parenchymatous cells with intercellular spaces.
Some of the cells have chloroplasts and are known as chlorenchyma.
Endodermis: The innermost layer of the cortex.
• It is made up of a single row of compact barrel-shaped cells without
intercellular spaces.
• The cells of endodermis store starch grains and so they are known as the
starch sheath. Casparian strips are distinctly visible in endodermal cells.
The vascular tissue of the stem consists of the complex tissues xylem and
phloem which carry water and nutrients up and down the length of the stem
and are arranged in distinct strands called vascular bundles.
Cambium is a strip of thin-walled cells that lie between the xylem and phloem
in dicot plants. Cambium is made up of merismatic cells and is responsible
for secondary growth. It is absent in monocots.

Functions of stem
• It supports and holds leaves, flowers, and fruits.
• The stem allows the leaves to arrange in a way that they are able to receive
direct sunlight in order to efficiently perform photosynthesis. The
arrangement and position of leaves also allow for gas exchange.
• The xylem and phloem present in the vascular bundles of stems conduct
water and minerals across the plant.
• Stems bear flowers and fruits in a position that facilitates the processes
of pollination, fertilization, and dispersion of seeds.
• Some stems undergo modification to store food and water. Example:
succulents.
• Few green stems contain chloroplasts and are capable of carrying out
photosynthesis as well.
• Some stems are modified to carry out vegetative propagation which is a
form of asexual reproduction seen in plants.

FLOWERS
• Plants are majorly classified on basis of presence or absence of flower into
flowering and non- flowering plants.
• A flower is a characteristic feature of flowering plants and is actually an
extension of the shoot meant for reproduction.
• Flowers are attractive and appear in different colours and shapes to attract
pollinators who help in pollen transfer.

• 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.
• Others may contain one of the two parts and
may be male or female.

Parts of flower
Peduncle: This is the stalk of the flower.
Receptacle: It is that part of the flower to which the stalk is attached to. It is small and
found at the centre of the base of the flower.
Sepals: These are the small, leaf-like parts growing at the base of the petals.
• They form the outermost whorl of the flower. Collectively, sepals are known as the
calyx.
• The main function of the calyx and its sepals is to protect the flower before it
blossoms(in the bud stage).
Petals: This layer lies just above the sepal layer.
• They are often bright in colour as their main function is to attract pollinators such as
insects, butterflies etc to the flower.
• The petals are collectively known as the corolla.
Stamens: These are the male parts of a flower. Many stamens are collectively known
as the androecium. They are structurally divided into two parts:
1. Filament: the part that is long and slender and attached the anther to the flower.
2. Anthers: It is the head of the stamen and is responsible for producing the pollen
which is transferred to the pistil or female parts of the same or another flower to
bring about fertilization.

Pistil: This forms the female parts of a flower. A collection of pistils is called the
gynoecium
Style -is a long slender stalk that holds the stigma. Once the pollen reaches the stigma,
the style starts to become hollow and forms a tube called the pollen tube which takes the
pollen to the ovaries to enable fertilization.
Stigma– This is found at the tip of the style. It forms the head of the pistil. The stigma
contains a sticky substance whose job is to catch pollen grains from different pollinators
or those dispersed through the wind. They are responsible to begin the process of
fertilization.
Ovary – They form the base of the pistil. The ovary holds the ovules.
Ovules– These are the egg cells of a flower. They are contained in the ovary. In the event
of a favorable pollination where a compatible pollen reaches the stigma and eventually
reaches the ovary to fuse with the ovules, this fertilized product forms the fruit and the
ovules become the seeds of the fruit.

FRUITS
• Fruits are a characteristic of flowering plants.
• Once pollination and fertilization occur, the ovary of
the plant becomes the fruit and the ovules become
the seeds.
• They can be fleshy or dry.
• The main purpose of fruits is that they protect the seeds
during development.
• Since they are often colourful and emanate a delectable
odour, they help in attracting birds and other animals to
eat seeds.
• This way the seeds get dispersed to other areas for
generating new plants.

Structure of a fruit
• The fruit primarily contains two parts: the pericarp and the seed. The pericarp layer
is actually the outer wall of the ovary from which the fruit developed. The pericarp
has three layers.
• Exocarp or Epicarp: This is the outermost layer of the pericarp that forms the
skin.
• Mesocarp: It is the thick, fleshy and juicy middle layer of the pericarp.
• Endocarp: It is the innermost layer of the fruit which often develops into the pith.

Classification of fruits
On basis of the number of ovaries and the number
of flowers involved in their formation, fruits are
broadly classified into three categories:
1. Simple Fruits
2. Aggregate Fruits
3. Multiple Fruits

Simple Fruits
• These fruits develop from a single ovary of one or more
carpels.
• These fruits are further divided into Dry fruits and
Fleshy fruits depending upon pericarp.
Aggregate Fruits
• These fruits develop from multiple ovaries but of the
same flower. So, an aggregate fruit consists of a
collection of simple fruits called as fruitlets.
• E.g Blackberries, strawberries.
Multiple Fruits
• They are formed by all the flowers of
an inflorescence which together result in a single big
fruit. Multiple fruits are called false or composite fruits.
• E.g Mulberries, pineapple.

SEED
• The seed in a plant is the part that develops from the ovules
after fertilization.
• They are enclosed in the fruit which develops from the fertilized ovary.
• The seeds are formed as a result of sexual reproduction and contain the
young embryo which can develop into a new plant.
Structure of a Seed
• Seeds of different plants may vary in many ways, but the basic anatomy
remains the same. A typical seed consists of the following parts

Tesla: It is the outer coat of the seed that protects the embryonic plant.
Micropyle: It is a tiny pore in the testa that lies on the opposite of the tip of the radicle.
It permits water to enter the embryo before active germination.
Hilum: Is a scar left by the stalk which attached the ovule to the ovary wall before it
became a seed.
Cotyledon: In some plants, this contains high quantities of starch and will provide
a source of food for the developing embryo prior to germination, in other plants this
role is performed by an endosperm. In monocotyledons,
There is just one cotyledon whereas in dicotyledons there are two. Depending on the
type of germination (epigeous or hypogeous) the cotyledons may remain below ground
or be pulled above ground.
Radicle: This is the embryonic root which will develop into the primary root of the
plant. It is usually the first part of the embryo to push its way out of the seed during
germination.
Plumule: This is the embryonic shoot. It appears as a bud which will give rise to the
shoot and the remaining structures in the plant.
Endosperm: In many plants, a separate part for storage of starch develops and this is
called the endosperm. It is seen in maize and wheat.

Functions of Seeds
• The seeds perform the following functions:
• They help in germination of the new plant.
• The seeds contain food reservoirs in the form
of cotyledons and endosperm.
• The seed coat is protective in nature which
protects the embryo inside.

ROOT
• The root is usually an underground part of the plant. It is
primarily responsible for the fixation and absorption of water.
The root with its branches is known as the root system
• The root is the descending portion of the plant axis.
• It is positively geotropic.
• It is usually non-green or brown in colour.
• The root is not further differentiated into nodes and internodes.
• As per the rule, the root does not bear leaves and tree buds.
• Usually, a root cap protects the root tip.
• The root bears unicellular root hairs.
• Lateral roots arise from the root. These are endogenous in
origin (arises from pericycle).

Types of Root System
• The root system is generally of two types. We will
look at these two types in the section below.
Taproot system: The taproot system develops from
radicle of the germinating seed.
It is also called the normal root system. The taproot
system is present in only dicotyledonous plants.
Adventitious root system: The root system that
develops from any part of the plant body other than
the radicle is called the adventitious root system.
It is mostly seen in monocotyledonous plants.

Regions of the Root
• Root Cap: The root cap is a thimble-like structure covering the tip
of the root. The root cap protects the tender root apex when it makes
its way through the soil. Regions of the Root
• Root Cap: The root cap is a thimble-like structure covering the tip
of the root. The root cap protects the tender root apex when it makes
its way through the soil.
• Region of Elongation: This part is responsible for the meristematic
activity. The cells in this region are very small, have a thin wall and
dense protoplasm.
• Region of Maturation: We get the root hairs in this region. These
are a part of the root epidermis.
• Region of Elongation: This part is responsible for the meristematic
activity. The cells in this region are very small, have a thin wall and
dense protoplasm.
• Region of Maturation: We get the root hairs in this region. These
are a part of the root epidermis.

Modifications of Root
• Food storage: Taproots of turnip and carrot are
examples where roots are modified for food storage.
• Support: In banyan trees, hanging roots come out
from branches. The hanging roots then go into the
soil to provide additional support to the huge banyan
tree.
• Respiration: In swampy plants, many roots come out
vertically above the ground. These are hollow roots
and their primary function is the exchange of gases in
the roots.

Basic principles of Pharmacognosy

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