Page 161 - Pharmacognosy 2 PG303

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

Belladonna, Althea etc.
2. Secondary roots: They are the lateral roots as in krameria.
3. Adventitous roots: They usually arise from the stem as in Ipecacuanha, jalap
etc.

Storage roots: These are the roots of any of the previously mentioned
types, which become swollen with reserve food materials. Swollen primary
roots occur in Belladonna, Carrot etc. Swollen secondary roots occur in
Asafoetida etc., swollen adventitious roots occur in Calumba, Ipecacuanha,
Jalap. Those which are very swollen e.g. Jalap, Aconite, Carrot etc. are called
root tubers or tuberous or tuberculated roots.

Roots which are used in medicine, occur in the market usually in the dried condition,
being entire or nearly entire as in Senega or sliced longitudinally as in some Althea
or transversely or obliquely as in Calumba or cut into small pieces as in some Althea.
They may occur in the peeled condition as in Althea and some liquorice etc.

Histology of Roots

The young root of the dicotyledons is histologically characterised by the following
features: It shows a much wider cortex than the stele. Externally there is a piliferous
layer, covering the parenchymatous cortex, the outer layer of which is sometimes
specially differentiated, being usually formed of small cells with thickened more or
less suberized, occasionally lignified walls and known as exodermis as in Smilax
ornata. The innermost layer of cortex, the endodermis, is generally well marked and
has either a strongly developed casparian strip or some special form of thickening.
The stele is surrounded by a single layer of pericycle and has bundles of xylem and
phloem arranged in a circle, alternating in position so that each lies on a different
radius. There is no cambium; at all in every young root. The pith is lacking in woody
dicotyledons where the central part is occupied by metaxylem elements but is present
in many herbaceous dicotyledons and in monocotyledon's; being usually represented
by thickened parenchyma or sclerenchyma. The xylem occurs in radial groups with
the protoxylem towards the periphery of the root, i.e. ex-arch. According to the
number of these groups, the root is described as di-arch as in Belladonna, ' Solarium
etc., tri-ach as in Gentian, Ipecacuanha etc. tetra-arch as in Liquorice, pent-arch as
in Vicia and poly-arch as in Sarsaparilla.

Secondary Thickening in Roots
The roots of pteridophytes and of the monocotyledons usually retain their
primary structure, showing distinct pith, often composed of thick-walled lignified
cells, porous xylem, wide cortex and frequently epidermis (piliferous layer) as
in Sarsaparilla. But in the gymnosperms and the Dicotyledons, secondary
thickening takes place as follows:

118