Subterranean Organs

Introduction Subterranean organs include There is no clear division between rhizomes and roots in a commercial sense. Subterranean stems Subterranean roots rhizomes corms Stem tubers bulbs roots root tubers

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.

Belladonna and Gentian 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.