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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