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Morphology and Histology of vishaghni - Alstonia venenata R. Br.

vishaghni - Alstonia venenata R. Br. - Apocynaceae

vishaghni :

vishaghni : Alstonia venenata R. Br.

Morphology:

Shrubs or small trees. Leaves 12-20 x 1.2-3 cm, linear-oblong, acuminate at both ends, 5 at each node, lateral nerves many, very close. Cymes terminal, to 20 cm across, corymbose. Flowers many; pedicels stout; sepals 1 mm long, ovate, acute, ciliate; corolla tube slender, hairy inside, lobes 13 mm long, oblong, acute, white. Follicle 2-angled, acute; seeds smooth.

Histology:

Microscopic features of the leaf

Midrib

The midrib has wide and short adaxial hump and

broadly hemispherical abaxial part. It is 650 µm in

vertical plane; the adaxial hump is 250 µm wide in

horizontal axis; the abaxial part is 600 µm wide. The

midrib has thin epidermal layer consisting of small

squarish thick walled cells. About three or four layers

of sub-epidermal cells are collenchymatous. Rest of

the ground tissue consists of parenchymatous, compact

cells. Wide secretary canals with uneven outline are

sparingly seen in the ground tissue. The vascular tissue

occurs in a single wide arc of bicollateral strand. It

consists of several radial parallel lines of thick walled

angular xylem elements; phloem occurs in small

clusters both on the abaxial and adaxial parts of the

xylem band.

Lamina

The leaf has even, smooth adaxial and abaxial

surfaces with prominent midrib and lateral veins. The

lamina is about 120 µm thick. The adaxial epidermis is

prominent comprising of squarish or cylindrical, thin

walled cells. The abaxial epidermis is thin with

narrowly cylindrical cells. Stomata occur on slightly

raised level of the epidermis. Mesophyll consists of

narrow zone of palisade cells and aerenchymatous

spongy parenchyma cells. The palisade cells are short,

measuring 40 - 50 µm in height; the cells are

cylindrical and less compact. The spongy parenchyma

cells are lobed and interconnected with each other with

wide air chambers. The lateral vein is prominent

projecting on the adaxial side measuring 150 µm thick.

It consists of a few vertical files of xylem elements and

a small arc of phloem; the vascular bundle is

surrounded by parenchymatous bundle sheath with

adaxial and abaxial extensions. The marginal part of

the lamina is slightly curved abaxially; the margin is

semicircular with palisade and spongy tissues. The

epidermal cells have short tubercles, especially on the

abaxial side.

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