The bark

Secondary Thickning

- In old dicot, secondary thickning takes place due to cambium activity.

- There are two types of meristematic cambium tissues

1- First meristematic cambium originate firstly within the parenchyma ofthe phloem giving vascular cambium.

2- Secondary meristematic cambium formed in the outer layer of pericylegiving cork cambium.

The secondary thickning occurs through two stages or two parts-

through activation ofry phloem2and ry xylem 2Formation of -Avascular cambium.

-vascular cambiun activate to give 2ry phloem to outside thus pushing the 1ry phloem outwards and 2ry xylem to the inside pushing the the 1ryxylem inside.

-Excessive growth occurs pushing 1ry phloem outwards and 1ry xylem inwards.

-2ry phloem may form ph.fibers with parenchyma cells arround it. - Medullary ray usually formed lignified in xylem and non lignified inphloem.

through acivation of corkphellodermand cork cell Formation of -Bcambium

-Cork cambium developed in the pericycle layer to form phellogen which give cork cell to outside and secondary cortex (phelloderm) to inside cutting off all the external tissues.

-ry cortex and piliferous layer are usually 1As a result, the endodermis, removed and thus becoming absent in old roots.

The bark is all tissues outside the vascular cambium.

So, when say, it is the dried inner bark means the drug consists of phloem only.

Bark Bark

Outer bark (cork

region).

Outer bark (cork

region).

Middle bark

(cortex region).

Middle bark

(cortex region).

Inner bark

(phloem region ).

Inner bark

(phloem region ).

Classification of bark

Shapes of the bark

Flat

Curved

Channelled

Doublequill

Singelquill

Compound quill

Cascara bark 1الكسكاراقشر-

Origin: It is the dried stem bark of Rhamnus purshianaFamily: Rhamnaceae

Macroscopical characters

Condition: dry and broken

Shape: quill, channeled or nearly flat pieces

Size: 20 cm long, 2 cm broad and 5 mm thick

Odour: slight and characteristic

Taste: bitter, nauseous and persistent

Microscopcal charactersT. S. shows a partial coat of whitish lichens

1-Cork: several layers of small thin-walled cells, flattened and filled with yellowish-brown content

2-Cortex: composed of collenchyma, parenchyma and groups of sclereids

Few layers of collenchyma, several parenchyma containing chloroplasts and starch granules and scattered cluster crystals of calcium oxalate abutting to them groups of sclereides and phloem fibers encircled by prismatic crystals of ca. ox.

3- Phloem: wide traversed by numerous wavy medullary rays (1-5 cells wide and up to 25 cells length)- Composed of sieve tubes, phloem parenchyma, fibers surrounded by sheath of prismatic crystals of ca. ox. and scattered cluster crystals

Powder

Yellowish-brown to reddish-brown with characteristic odour and bitter taste

Microscopically

1- Groups of fibers surrounded by parenchyma cells containing prisms of ca ox forming crystal sheath, each fiber is narrow with narrow lumen, thick lignified walls and few pits

2- Groups of sclereids which are rounded to elongated, the walls are thick lignified with narrow lumen and surrounded by crystal sheath

3- Fragments of cork which are polygonal cells filled with reddish-brown content

4- Parenchyma cells containing small spherical starch granules, prism and clusters of ca ox

5- Occasional fragments of liverworts and mosses

Active constituents

Anthracene derivatives (6-9%) as O-glycosides and C-glycosides

1- Four primary glycosides or cascarosides A, B (8-O-glycosides of aloin A, B), C and D (crysophanol instead of aloe-emodin)

2- Two aloin (aloe-emodin anthrone, C-glycosides)

3- Aloe-emodin, chrysophanol and emodin in free state

4- Glycosides of emodin, emodin anthrone, aloe emodin and chrysohanol (O-glycosides)

Uses

1- As purgative

2- Cathartic if freely given

3- Tonic and stomachic small dose

2-Frangula bark

Origin: It is the dried stem bark of Rhamnus frangula

Family: Rhamnaceae

G.S.: UK and Europe, Russia

The difference between Cascara and Frangula

Cascara FrangulaSclereids Present AbsentLichens and moss Present OccasionalFibers 8-15 u 40 uMedullay rays 1-5 cells wide,

up to 25 cells high

1-3 cells wide, 10-25 cells high

Fibers of crystal sheath

8-15 u wide 12-24 u wide

Test for anthraquinones

Orange red Cherry red

Mucilage in the cortex absent Present

Active constituents

Anthraquinones derivatives free or as glycosides (1 %) O-glycosides only

1- Franguloside A, B

2- Fresh bark contains anthranols and anthrones

3- Frangula emodin, chrysophanic acid and iso-emodin derivatives

Uses

1- As laxative preferable than cascara as it is less disagreeable

Cinchona bark الكیناقشر

Origin:

It is the dried stem and root bark of Cinchona succirubra, Cinchona Ledgeriana, Cinchona calisaya and Cinchona officinalis Family: Rubiaceae

G.S.: South America (Venzuela, Peru, Equador and Bolivia), Now grown in India, Congo

3- Cinchona bark الكیناقشر

Macroscopical characters

Condition: dry

Stem bark

Shape: quills, double quills, curved pieces and chips

Size: 30 cm long, 1-4 cm wide and 2-9 mm thick

Odour: faint and characteristic

Taste: bitter to very bitter and astringent

Microscopical characters

Stem bark

Cork: thin-walled rectangular cells with brownish content and bearing dense masses of lichens on the outer surface

Cortex: narrow, composed of parenchyma cells with brownish walls contain few starch granules and showing numerous idioblasts of microspenoidal crystals of ca ox.

In the inner part, there is a row of long laticiferous tubes

Phloem: thin walled cells traversed by medullary rays 1-3 cells wide, showing numerous fibers isolated or in small groups. The fibers are spindle shape with narrow lumen, strongly lignified with funnel-shaped pits and blunt tips

PowderReddish-brown with slight characteristic odour and bitter

and astringent tasteMicroscopically1- Abundant fibers, yellowish colour, fusiform in shape,

blunt pointed end, lignified with funnel-shaped pits2- Fragments of cork which are polygonal cells filled with

dark red to brown content3- Parenchyma cells containing small spherical starch

granules, microsphenoiod crystals of ca ox

Active constituents1- Quinoline alkaloids (6-10%) (more than 30 alkaloids)The four most important alkaloids are: quinine, quinidine, cinchonine and cinchonidine in combination with quinic and cinchotanninc acid 2- Tannins (cinchotannic acid, phlobatannin)3- Quinic acid4-Quinovin bitter amorphous glycoside

The root bark is the richest in alkaloidal content and the stem bark is richer than branch bark

Uses1- Quinine is used for the treatment of malaria2- Quinidine is used for the prophylaxis of cardiac arrhythmia3- Cinchonine and cinchonidine are used as antirheumatic4- Bitter tonic and stomachic 5- Due to astringent action, decoction is used as gargles

Cinnamon bark 4قشر القرفــة-

Origin: It is the dried inner bark of the shoots of Cinnamomum zeylanicum

Family: Lauraceae • Deprived of most of its cortex• G.S.: Ceylon

Cinnamon bark قشر القرفــة

• Macroscopical characters• Condition: dry• Shape: channeled pieces,

compound quills• Size: different length and

about 6-10 mm in diameter• Odour: fragrant and aromatic• Taste: sweet, agreeable

and warm

Microscopcal characters

• T. S. shows an outer paler layer of pericyclic sclerenchyma and an inner darker phloem traversed by fine medullary rays

• Cork: absent

• Cortex: absent

Microscopically1- Abundant sclereids more or less isodiametric, lignified, some with unequal thickening, pits are numerous and conspicuous and striations are visible, some contain starch granules

2- Abundant fibers which are colourless, usually occur singly, lignified with slit-shaped pits

3- Parenchyma cells containing starch granules which are simple or compound with round or slit shape hilum;

in addition to acicular crystals of ca ox4- Thin-walled oil cells occur singly

frequently associated with parenchyma or fibers of the phloem

Active constituents

1- Volatile oil (0.4-1.2%) contain 65% cinnamic aldehyde and 4-10% eugenol

2- Tannins 1% (phlobatannins)

3- MucilageUses1- Carminative2- Flavouring agent3- Mild astringent4- Aromatic antiseptic and antifungal5- Cinnamic aldehyde is used as hypotensive agent (by peripheral vasodilatation)

Cassia bark 5قشر الكاشیة-

Origin:

It is the dried stem of Cinnamomum cassia Family: Lauraceae

G.S.: Vietnam and south china, cultivated in other parts of eastern China and Asia

5-Cassia bark

Microscopcal charactersT. S. similar to that of cinnamon but it contain the cork

and the cortex

The difference between Cinnamon and CassiaCassiaCinnamon

PresentAbsentCork and cortex

More than 30 uLess than 30 uFibers diameter

More than 10 uLess than 10 uStarch diameter

270230 uTotal fiber length

Up to 1.50.5-1.2Volatile oil percent

85%60%Cinnamic aldehyde

Nil4-10%Eugenol content

10%1.6-2.9Mucilage

Active constituents

1- Volatile oil (not less than 85% cinnamic aldehyde and no eugenol)

2- Tannins (phlobatannins)

3- Mucilage

4-Flavanol glucoside

Uses1- Carminative

2- Flavouring agent

3- Mild astringent

4- Anti ulcerogenic activity

5- Substitute for cinnamon