CLOVE
Synonyms: Clove flower, Clove buds, Laung (Hindi)
Biological
Source: Clove consists of the dried flower buds of Eugenia
caryophyllus, belonging to family : Myrtaceae.
Macroscopy
:
Fig. Clove Flower Bud
Clove is reddish-brown in colour, with an upper crown and a hypanthium.
The hypanthium is sub-cylindrical and tapering at the end. The hypanthium is 10 to 13 mm long, 4 mm wide, and 2 mm thick and has schizolysigenous oil glands and an ovary which is bilocular.
The Crown region consists of the calyx, corolla, style and stamens. Calyx has four thick sepals. Corolla is also known as head, crown or cap; it is doineshaped and has four pale yellow coloured petals which are imbricate, immature, and membranous.
The ovary consists
of abundant ovules.
Clove has strong spicy, aromatic
odour, and pungent and aromatic taste.
Microscopy:
In the case of clove bud, a transverse section is
taken through the ovary as well as through
the hypanthium, i.e.
stalks of the
bud. The short
upper portion present immediately below the calyx contains
bilocular ovary. The lower portion, i.e. stalk of the bud
(hypanthium) that lies
at the lower
part, is long,
solid and sub-cylindrical. The transverse
section through the
hypanthium shows the
following tissues microscopically
from the periphery towards the centre:
Fig. T.
S. of Clove Flower Bud
Epidermis:
It is made
up of a single layer
of small, tabular
cells with straight
walls and highly cuticularised. It
shows presence of
anomocytic (ranunculaceous) type
of stomata. These stomata
appear as slightly
raised above the
epidermal surface. The substomatal spaces are prominent and well
defined.
Cortex:
It occupies the major portion and can be divided into three different zones:
i.
Outer
Zone: It shows two to three layers of big, ellipsoidal,
schizolysigenous oil glands embedded in radially elongated parenchymatous
cells. Oil glands have long radial axis and an epithelium which
is composed of
two or three
layers of flattened
cells. Parenchymatous cells contain
tannins and thus
show dark colouration
with ferric chloride solution
(alcoholic). Many of the parenchymatous cells show cluster crystals of calcium
oxalate.
ii.
Middle
Zone: Within the oil gland layer, a zone of thick-walled
cells is seen. Within these cells, a ring of bicollateral vascular bundles is
embedded. About 20–25 bundles are present in
the ring. The
ground tissue contains
cluster crystals of
calcium oxalate. The vascular bundles are enclosed in an
incomplete ring of lignified pericyclic fibres. The xylem is composed of three
to five lignified spiral vessels.
iii.
Inner
Zone: It is made up of loosely arranged parenchymatous
cells (aerenchyma) composed of air spaces. Air spaces are separated by lamellae
which are thin and one cell thick. This region supports the central columella.
Columella: It
forms the central cylinder which is parenchymatous and contains calcium oxalate
crystals. A ring
of about 15–20
small vascular bundles
is seen towards
the periphery.
The
transverse section through the ovary shows all tissues described above. But
instead of the
central columella, a
bilocular ovary is
present at the
centre. The ovules are
numerous, separated by
an axile placentation.
The dissepiments of the
ovary is
parenchymatous. The placentae
show cluster crystals
of calcium oxalate and vascular bundles.
Powder Character:
The powder
of the clove
buds is dark
brown in colour
and possesses a characteristic, spicy aroma and pungent,
slightly, characteristic, aromatic taste. The powder shows the following
characters microscopically:
i. Hypanthium: The fragments of hypanthium and the epidermis occur abundantly. The epidermis is made up of small, polygonal, thick-walled cells. It shows circular, big, anomocytic stomata along with large, brown, ovoid oil glands. A few cluster crystals of calcium oxalate are also observed. The fragments of hypanthium show a thick cuticle.
ii. Oil Glands: These are numerous in the hypanthium, ellipsoidal to ovoid, large, brown and schizolysigenous associated with other parenchymatous tissues.
iii. Parenchyma: The yellowish-brown parenchyma of hypanthium is abundant. Oil glands are found as embedded in this area. Cells are thickened and sometimes are collenchymatous.
It shows a few small cluster crystals of calcium oxalate.
iv. Calcium Oxalate Crystals:
The cluster crystals of calcium oxalate (sphaeraphides) are found in the parenchymatous cells. These crystals are of various sizes, rarely found scattered and made up of many small components.
v. Fibres: These are sclerenchymatous, found singly or in groups of two to three in each group. These are short, broad and bluntly pointed. These show lignified thick walls with faint striations and small pits. The lumen is sometimes filled with brownish matter. These fibres are generally associated with parenchymatous cells or with small groups of vessels (fibrovascular bundle).
vi. Aerenchyma:
Fragments of aerenchyma (loosely packed parenchyma) of the hypanthium are occasionally observed. These are made up of chains of two or three thick- walled parenchymatous cells. These chains show small intercellular air spaces separated by lamellae.
Fig. Powder Microscopy of Clove Flower
Bud
1. 1. Part of the filament of the anther in
longitudinal section, showing the central vascular strand and parenchymatous
cells containing cluster crystals of calcium oxalate.
2. 2. Part
of the hypanthium
in sectional view
showing the thick
cuticle, epidermis and underlying parenchyma with oil glands.
3. 3.Parenchyma of the hypanthium with
cluster crystals of calcium oxalate
4. 4. Fragments of aerenchyma from the
hypanthium showing pits
5. 5. Epidermis of
the hypanthium in
surface view showing
a stoma and underlying oil glands
6. 6. Parenchyma of the hypanthium showing an
oil gland
7. 7. Epidermis of
a petal in
surface view with
underlying tissue composed
of parenchymatous cells containing
cluster crystals of
calcium oxalate, part
of an oil gland and part of a vascular strand
8. 8.Mature Pollen grains
9. 9. Fibrous layer of the anther in surface
view
1010. Part of group of immature pollen grains
1111.
Fibrous layer of the anther In sectional
view
1212. Sclereids from the stalk
1313. Epidermis of the filament of the anther
in surface view
1414. Fibrous and associated parenchymatous
cells
i.
Sclereids:
These
are from stalk and appear as oval to sub-rectangular with thick, striated walls
and simple or branched pits. Some brownish matter is found inside the lumen.
ii.
Pollen
grains: These are small and biconvex with rounded or triangular
shape and smooth exine. The immature pollen grains are found inside the
pollen sacs.
iii.
Starch
grains: Starch grains are not observed in the case of the
powder of clove buds. If these are observed in the powder, these come from
mother cloves.
Chemical Constituents:
Clove contains
14–21% of volatile
oil. The other
constituents present are
the eugenol, acetyl eugenol, gallotannic acid, and two crystalline principles;
α- and β- caryophyllenes, methyl furfural,
gum, resin, and
fibre. Caryophyllin is odourless component and appears to be a
phytosterol, whereas eugenol is a colourless liquid. Clove oil
has 60–90% eugenol,
which is the
cause of its
anesthetic and antiseptic properties.
Chemical
Tests:
1.
To
a thick section
through hypanthium of
clove add 50%
potassium hydroxide solution; it
produces needleshaped crystals of potassium eugenate.
2.
A drop of clove oil is dissolved in 5 ml
alcohol and a drop of ferric chloride solution is added; due to the phenolic OH
group of eugenol, a blue colour is seen.
3.
To a
drop of chloroform
extract of clove
add a drop
of 30% aqueous
solution of sodium hydroxide
saturated with sodium bromide; Needle and pear shaped crystals of sodium
eugenate arranged in rosette are produced immediately.
Uses:
Clove is used as
an antiseptic, stimulant, carminative, aromatic, and as a flavoring agent. It is also
used as anodyne,
antiemetic. Dentists use
clove oil as
an oral anesthetic and to
disinfect the root
canals. Clove kills
intestinal parasites and exhibits broad antimicrobial properties
against fungi and bacteria and so it is used in the treatment
of diarrhea, intestinal
worms, and other
digestive ailments. Clove
oil can stop toothache. A few drops of the oil in water will stop
vomiting, eating cloves is said to be aphrodisiac. Eugenol is also used as
local anaesthetic in small doses. The oil
stimulates peristalsis; it
is a strong
germicide, also a
stimulating expectorant in bronchial problems. The infusion and Clove
water are good vehicles for alkalies and aromatics.
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