tvak :

Morphology:

Bark

· pieces about 0.5 mm thick, brittle,

· occurs as single or double, closely packed compound quills,

· upto a metre or more in length and upto about 1 cm in diameter,

· outer surface, dull yellowish-brown, marked with pale wavy longitudinal lines with occasional small scars or holes,

· inner surface darker in colour, striated with longitudinally elongated reticulation, fracture, splintery, free from all but traces of cork,

· odour, fragrant, taste, sweet, aromatic with sensation of warmth.

Histology:

Transverse section of bark (devoid of cork and cortex)

· shows except at certain places pericyclic sclerenchyma,

· 3 or 4 rows of isodiametric cells,

· sometimes tangentially elongated,

· inner and radial walls often being thicker than the outer,

· some containing starch grains,

· small groups of pericylic fibres embedded at intervals in the sclerenchyma,

· phloem of tangential bands of sieve tissue alternating with parenchyma, and containing axially elongated secreting cells containing volatile oil or mucilage, phloem fibres with very thick walls, upto 30 µ in diameter, isolated or in short tangential rows, sieve tubes narrow with transverse sieve plates, collapsed in outer periphery,

· medullary rays of isodiametric cells, mostly 2 cells wide, cortical parenchyma and medullary rays containing small starch grains mostly below 10 µ in diameter,

· minute acicular crystals of calcium oxalate present.