Pharmacognosy: Bark Structure and Types

Bark

• Bark is the outermost layers of stems and roots of woody plants.
• A regular stem consists of epidermis, cortex, endodermis, pericycle, phloem, cambium, and xylem.
• Bark consists of cork, phellogen, phelloderm, cortex, and phloem.

Cinchona Bark

• Origin: Dried stem and root bark of Cinchona succirubra (Red Cinchona), Cinchona ledgeriana (Yellow Cinchona), and Cinchona officinalis (Pale Cinchona) from the family Rubiaceae.
• Composition: Lignified fusiform phloem fibers, cork cells, parenchyma containing starch grains, and parenchyma containing microcrystals of calcium oxalate.
• Active Constituents: Quinoline alkaloids (quinine, quinidine, cinchonine, and cinchonidine), glycosides, tannins (cinchotannic acid), and bitter principles.
• Uses: Quinine is used as an antimalarial agent, quinidine is used as an anti-arrhythmic agent, cinchonine and cinchonidine have anti-rheumatic properties, and cinchona powder is used as a tonic and bitter stomachic.
• Chemical tests for identification: Mayer's test for alkaloids and dry heat test.

Cinnamon Bark and Cassia Bark

• Origin: Dried decorticated bark of Cinnamomum zeylanicum (Family Lauraceae) for Cinnamon bark and dried stem bark of Cinnamomum cassia (Family Lauraceae) for Cassia bark.
• Composition: Cinnamon powder contains oil cells, sclereids, lignified fusiform phloem fibers, parenchyma containing small starch grains, and parenchyma containing acicular crystals of calcium oxalate.