Page 99 - Pharmacognosy 2 PG303

Pharmacognosy-2 (PG303) Level 2 Clinical Pharmacy-Pharm D

Aerial stem:
The aerial stem carries leaves and flowers in a manner to favor their functions. It acts for
conducting water and mineral nutrients from the root to the leaves and the elaborated food from
the leaves to the root and in certain cases when the leaves are reduced, it serves for assimilation.

I- Morphological characters

1- Shape:

1- Cylindrical or nearly cylindrical e.g. Euphorbia.
2- Angular have angles and sides so it may be triangular, quadrangular e.g. Mentha and

pentagonal.
3- Winged e.g. Lobelia.
4- Ribbed marked with alternate ridges and furrows as in Broom Tops.
5- Grooved and more or less collapsed due to shrinkage during drying as in Belladonna and

Henbane.

2- Color:

The color may be green as in Broom Tops, pale green with purple patches as in Lobelia,
brownish with purple patches as in Euphorbia pilolifera.

3- Type:

1- Herbaceous: The stem is soft, easily broken and has smooth or hairy surface. Mostly the
plant is annual and composed mainly of primary elements (i.e., stem shows little or no
secondary thickening).

2- Succulent: It is thick fleshy as Euphorbia.
3- Woody: It is hard of subshrub and trees and usually covered by cork.
4- Creeper: The main axis extends along the ground where each node gives an aerial shoot

and adventitious root as in Ground Ivy.
5- Runner: Similar to creeper but the shoots and rootlets arise from the nodes of lateral (not

the main axis) prostrated branches e.g., Strawberry.
6- Sucker: Like runner but the branch here arises and grows below the level of the ground but

later becomes aerial as in Mentha.
7- Climber: Stem is so weak that it attaches itself to any support by means of tendrils as in

Vitis or by hooks as in Hops or by adventitious roots as in Piper.
8- Twining: Stem similar to climber, but the stem attaches itself to a support by winding itself

around it e.g., Convolvulus.

4- Branching:

There are two chief types of branching, axillary or lateral and dichotomous or apical.
1- Axillary or lateral: the branches develop from lateral buds in the axil of the leaves as in

Angiosperms. It may be either monopodial or sympodial.
a- Monopodial or racemose (indefinite) branching: when the main axis continues
growing from the apical bud, giving off lateral branches never exceed its length.
b- Sympodial or cymose (definite) branching: when the main axis stops growing from
the apical bud due to flower or tendril formation and instead, one or more axillary bud
grows to add new branches.
2- Dichotomous or apical: when the growing point is divided into two halves grow out into
two equally strong branches and so on as in thallophytes e.g. Chondrus.

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