Transcript Subterranean Organs - Suez Canal University

Subterranean Organs
Introduction
Subterranean organs include
Subterranean stems
rhizomes
corms
Subterranean roots
Stem
tubers
bulbs
roots
root
tubers
There is no clear division between rhizomes
and roots in a commercial sense.
• Subterranean organs used in medicine
are usually collected from perennial
plants where they serve as storage
organs and thus generally are full of
reserve food materials.
• They are usually rich in carbohydrate
such as starch (eg filix mas, rhubab),
sugars (Gentian and squill), inulin
(family compositae) and they are devoid
of chlorophyl.
Subterranean stems
• Characterized by:
– Scaly leaves
– Axillary buds (in the axis of scaly leaves)
– Adventitious roots
– A growing point protected by scale
leaves forming a bud.
Drug obtained in the market from sub. Stems occur in
the form of entire, broken pieces, longitudinal slices,
transverse slices, partially or wholly decorticated.
Types of subterranean stems
1- Rhizome
• Most important and most common member of the group
regarding medicinal value
• Underground stem with nodes and internodes, long or
short, terminal buds and aerial shoots.
• Grow horizontally with the roots on the lower side and
the scale leaves and buds of aerial shoots on the upper
side. E.g. Podophyllum
• Sometimes grow vertically with the roots and scale
leaves all over the surface, which is usually annulated
e.g. valerian and occasionally grow obliquely e.g. Felix
mas.
1. Rhizome
• Sucker:
A type of rhizome which is a branch growing
under the ground, arising from the stem or from
the top of the roots and giving off roots and
aerial shoots at the nodes.
• Stolon:
Underground stem which travels near or below
the surface of the soil and roots at its extremity.
It is much thicker than a runner.
2. Corm
• Shortened swollen erect underground
stem, covered with brown scale leaves
arising at the nodes and usually having
a large apical bud and small axillary
ones.
• The daughter corn is protected below
the large apical bud
3. Stem tuber
• Swollen underground stem or part
of a stem, usually the tip.
• It differs from the root tuber in
bearing several small scales and
buds as well as the terminal bud
on the free end.
• It is full of reserve food materials
4. Bulb
• Underground stem reduced to a small
flattened disc and is crowned with fleshy scale
leaves and having adventitious roots arising
from the base of the bulb
• A bulb may be a scaly bulb or tunicated bulb
• In the scaly bulb, the fleshy scales nearly
overlap at their margins i.e. the outer scales
do not encircle the inner ones. In the tunicate
bulb the outer scales are completely
ensheathing the inner portion of the bulb
Histology of subterranean stems
• Generally resemble in structure aerial stems
(epidermis, cortex, endodermis, pericycle, xylem,
phloem, pith)
Histology of subterranean stems
• Generally resemble in structure aerial stems
(epidermis, cortex, endodermis, pericycle, xylem,
phloem, pith)
• In dicot.
They show
large pith
and
wide
cortex,
formed mostly of thin-walled parenchyma
packed with reserve materials.
• The cortex
is traversed by few vascular bundles
and the endodermis is usually indistinguishable
with few exceptions.
• Vascular bundles are closed, separated with wide
medullary rays and forming a single ring around the
pith.
Histology of subterranean stems
•In monocot. The structure differs
from that of the aerial stem
• It shows a distinct endodermis
separating the cortex from the
central stele.
• Vascular bundles are closed,
numerous and scattered in the
cortex and stele.
Histology of subterranean stems
In monocot
Subterranean roots
• The root is the part of the plant axis,
which grows vertically downwards in
seedlings, into the soil and away from
the light.
• It does not show nodes or internodes
• It does not bear leaves or buds.
• Its growing point is covered by a
special tissue called root cap or
calyptra.
Subterranean roots
• The root bears branches, which are
similar in structure and in general
characters to the main root.
• The branching of the root is usually
lateral and the lateral branches are
thinner and less strong than the
parent root.
Zones of a root
1. The
growing point: covered by the
root cap
2. The zone of elongation: where
the increase in the length of the root
takes place.
3. The zone of absorption or zone
of root hairs.
4. The zone of lateral roots:
which constitutes the majority of the
root.
Types of roots
1. Primary roots: develop into tap roots e.g. senega
2. Secondary roots: they are the lateral roots e.g.
Krameria
3. Adventitious roots: they usually arise from the
stem e.g. Ipecacuanha, Jalap
4. Storage roots: they occur when the roots of any of
the previously mentioned types becomes swollen
with reserve food materials. Those which are very
swollen e.g Jalap, aconite and carrot are called root
tubers or tuberous or tuberculated roots.
Types of roots
Storage roots
Adventitious roots
Histology of subterranean roots
• The young dicot. Shows:
– A cortex , much wider than the stele.
– Externally, there is a piliferous layer
covering the parenchymatous cortex
– The outer layer of the cortex is sometimes
specially differentiated and is usually
formed of small cells with suberised,
occasionally lignified walls known as
exodermis
– The endodermis is well marked
–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 each
lies on a different radius
–The xylem occurs in radial groups
with the protoxylem towards the
periphery of the root i.e the exarch
and according to the number of
xylem groups, the root may be
described as diarch, triarch, tetrarch,
pentarch or polyarch.
Histology of subterranean roots
Histology of subterranean roots
Secondary thickening in roots
• In dicto, sec. thickening takes place:
– The cambium is originated in the
parenchyma on the inside of the phloem
groups and outside the protoxylem
appearing, when these cambia unite, as a
wavy ring
– The cambium give xylem inwards and more
phloem to the outside, thus pushing the
primary phloem outwards
• Opposite each protoxylem group, the
cambium produces parenchyma only
forming primary medullary rays
• With the formation of much secondary
tissue, the primary phloem is crushed and
becomes hardly distinguished
• At the same time, a phellogen is developed
in the pericylic region giving cork to the
outside and phelloderm to the inside
• As a result, in older roots, the the
endodermis, primary cortex and piliferous
layer are thrown off and absent
Anomalous (irregular) structures in
subterranean organs
Rhubarb
• Abnormal
bundles
are
produced in the pith in the
form of radiating structures
called star spots, consisting
of a central dark spot of
collapsed
premedullary
phloem surrounded by an
abnormally
developed
cambium,
giving
phloem
inwards and xylem outwards,
with radiating slightly curved
medullary rays.
Anomalous (irregular) structures in subterranean organs
Aconite
• The cambium retains the
stellate form and only little
secondary xylem and very
little phloem. It also shows
wide medullary rays and
well-developed
parenchymatous pith. The
tegumentory tissue is not
formed of cork cells but of
irregulary
arranged
suberized cells derived from
the outer layer of cortex
forming the metaderm
Anomalous (irregular) structures in subterranean organs
Senega
• Irregulary
wedged
wood
due
wide
parenchymatous
medullary rays. The
sec.
phloem
is
abnormally developed
at
one
place,
producing an external
ridge the keel.
Anomalous (irregular) structures in subterranean organs
Belladonna
and Gentian
• The xylem is well
developed
and
constitutes the main
part of the root. It is
formed
mainly
of
parenchyma
with
scattered groups of
vessesls.
Several
abnormally developed
islands of interxyalry
phloem
are
also
present
Anomalous (irregular) structures in subterranean organs
Jalap
• Tertiary cambia in
the form of circles,
curves or concentric
rings,
producing
only parenchyma on
both
sides,
are
developed in the
wide
parenchymatous
xylem and enclosing
a few of the xylem
vessels
D: Jalap
Anomalous (irregular) structures in subterranean organs
Orizaba Jalap
• The
original
cambium
is
replaced and the
roots increases in
size by successive
cambia of a limited
period of activity
developed in the
pericyle, producing
vascular bundles in
rings
Anomalous (irregular) structures in subterranean organs
Dandelion
• The xylem is small
and central and
surrounded
by
unusually
developed phloem,
formed
of
concentric rings of
sieve tissue and
laticiferous vessels
alternating
parenchyma
C: Dandelion
Anomalous (irregular) structures in subterranean organs
Ipecacuanha
• The xylem is small
and
dense,
the
phloem is weakly
developed
as
a
narrow wedged ring
around the xylem
and a very wide
starchy
parenchymaotus
phellodrem
constituting
the
secondary cortex is
present.