Menispermaceae Classification Essay
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Here is a compilation of essays on the ‘Root’ for class 11 and Find paragraphs, long and short essays on the ‘Root’ especially written for school and college students.
Essay on the Root
- Essay on the Meaning of Root
- Essay on the Characteristics of Roots
- Essay on the Classification of Root
- Essay on the Regions of a Typical Root
- Essay on the Modification of Roots
- Essay on the Functions of Roots
- Essay on the Economic Importance of Roots
Essay # 1. Meaning of Root:
Root is the descending part of plant which generally penetrates inside the soil and serves the function of fixation and absorption. The root which develops from the radicle is called primary root. The primary roots giving rise to lateral branches are called secondary branches, those become further branched and called tertiary branches. The primary root along with its branches forms primary or normal or tap root system (Fig. ).
The root branches arise from an inner layer (pericycle) i.e., endogenous in origin. [While the shoot branches arise from the superficial layer (cortex) i.e., they are exogenous in origin]. Sometimes roots arise from anywhere (node of stem or on margin of leaves) except the radicle are called adventitious root.
In most of the monocotyledons, the primary root either dies very early or its growth becomes arrested and new roots develop from the base of the radicle are called seminal roots. These roots grow and behave as primary roots.
Later on, a number of roots develop from the base of the plumule or from its lower nodes. These roots are fibre-like and are called fibrous roots and they are collectively form fibrous root system (Fig. ). In cereals, the primary and seminal roots do not die quickly and usually persist, though the fibrous roots perform the main function.
Sometimes the plants are entirely rootless. They may be of different groups, viz., all thallophytes, bryophytes, some aquatic pteridophytes (Salvinia cuculata, 5. natans) and some angio- sperms like bladderwort (Utricularia stellaris of Lentibulariaceae), Wolffia arrhiza of Lemnaceae, Epipogum sp. of Orchidaceae, Myriophyllum indicum of Haloragidaceae etc.
Essay # 2. Characteristics of Roots:
1. Roots are usually non-green and conical in shape.
2. They are usually negatively phototropic (grow away from light), positively geotropic (grow in the direction of gravitational force) and positively hydrotropic (grow in water medium).
3. They do not bear leaves, flowers, except a few cases.
4. They develop branches of endogenous origin (develop from pericycle).
5. The growing apex is normally protected by a cap, called root cap or calyptra (Fig. A, B). In some water plants, an elongated cap-like structure (like a finger of a glove) develops at the apex, called root pocket (Fig. C, D).
6. The root cap may be simple (banyan, Ficus benghalensis of Moraceae; Amaryllis of Amaryllidaceae) or multiple (screw pine, Pandanus foetidus of Pandanaceae). [During growth, the root forces its way through the soil. At that time, the outer surface of cap becomes gelatinous and secretes a slimy substance to minimise the friction with the soil particles. With further growth the old root cap withers away and new root cap develops at the apex. The root pocket, unlike root cap, does not arise from epiblema and does not show regular renovation.]
7. Normally the root consists of four regions (Fig. ).
(i) Root cap,
(ii) Growing region,
(iii) Root hair region, and
(iv) Permanent region.
[Root hairs are the unicellular structure, visible with naked eye. The root hairs normally live a few days to a few months or rarely even few years in some members of Asteraceae.]
8. Some minor modifications are often available with the roots growing in different environmental conditions.
a. The aquatic roots do not bear root hairs.
b. The epiphytic root (in some orchids) develops a special kind of absorbing sheath, the velamen (Fig. A).
c. The xerophytic plants (plants grow in dry condition like desert) normally have deep root system to get more water and some have an additional superficial root to absorb atmospheric precipitation like rain etc.
d. The halophytic plants (plants grow in saline soil at or near the sea coast region) have negatively geotropic aerial roots with many pores, called pneumatophores (Fig. ) or respiratory roots in addition to normal root system.
Essay # 3. Classification of Root:
According to structure and mode of development, the roots are classified into two types.
1. Tap Root (Fig. B):
It forms by the continuous growth of radicle and is usually found in dicotyledonous plants, e.g., mango (Mangifera indica of Anacardiaceae).
2. Adventitious Root (Fig. B):
The roots neither develop from radicle nor primary roots and are called adventitious roots. They may develop from any other region of the plant body, viz. (i) from leaves, e.g., Bryophyllum calycinum and Kalanchoe laciniata of Crassulaceae, (ii) from stems, e.g., Zea mays (maize), Bambusa tulda (bamboo) and Saccharum officinarum (sugarcane) of Gramineae and (iii) from lower end of stem cuttings, e.g., Hibiscus rosasinensis (china-rose) of Malvaceae, Rosa centifolia (rose) of Rosaceae etc.
[The schematic representation of various types of roots has been given in Table ].
Essay # 4. Regions of a Typical Root:
A typical root has the following regions (Fig. ):
1. Root Cap Zone:
At the apex of the root a cap-shaped structure is present, called root cap. It gives protection to the young apical region during growth of root against soil particles.
2. Growing Region or Meristematic Zone:
This region lies just above the root cap region. Growth of the roots at this region takes place by mitotic cell division and cell elongation.
This zone consists of two regions:
(a) Region of cell division, and
(b) Region of cell elongation.
The cells of this region are thin walled with dense cytoplasm and with single large nucleus.
3. Root Hair Region:
This region is situated just behind the growing region and is covered by unicellular root hairs. The root hairs serve the functions of both anchorage and absorption of water and solutes.
4. Permanent Region:
It is the region situated behind the root hair zone. The growth of this region is seized. It serves the function of anchorage and translocation of substances absorbed by root hairs.
Essay # 5. Modification of Roots:
In addition to normal functions like anchorage and absorption of water with minerals, roots perform some special functions for which they get modified in various ways:
A. Modified Tap Roots:
The tap roots are completely or partially modified according to their functional need.
(a) For Storage of Food-Matters:
Due to accumulation of reserve food, the tap roots become fleshy and swollen and assume different shapes.
These are of Four Different Types:
These roots are thick in the middle and gradually taper at both the ends. On both the sides, secondary and tertiary roots are developed (Fig. A), e.g., radish (Raphanus sativus) of Brassicaceae.
These roots are broadest at the base and gradually taper at the lower end (Fig. B), e.g., carrot (Daucus carota of Apiaceae).
These roots get much swollen above, but abruptly taper towards the lower end (Fig. C), e.g., beet (Beta vulgaris of Chenopodiaceae), turnip (Brassica rapa of Brassicaceae).
These roots get swollen in any portion, thus they do not have a regular shape (Fig. D), e.g., Ruellia tuberosa of Acanthaceae, 4o clock plant (Mirabilis jalapa of Nyctaginaceae).
(b) For physiological functions (centre for N2 fixation, respiration etc.)
i. Nodulated Root:
The nodules are formed on the main root as well as on the branches (Fig. E). These nodules contain nitrogen-fixing bacteria. Viz., different members of Leguminosae (Fabaceae) such as gram (Cicer arietinum), garden pea (Pisum sativum) etc.
ii. Respiratory Root:
These are the branches of normal tap root system; those grow vertically above the soil or water- level (negatively geotropic) for respiration. The apices of these roots have many pores (pneumathodes) on their wall, through which air is conducted down into the subterranean roots.
These negatively geotropic roots are called pneumatophores or respiratory roots (Fig. A, B). These are found in halophytes (plants grow in saline soil) such as Rhizophora mucronata, Ceriops roxburghiana of Rhizophoraceae, Sonneratia apetala of Sonnaratiaceae, Heritiera minor of Sterculiaceae, etc.
B. Modified Adventitious Roots:
The adventitious roots are variously modified for different functions:
(a) Mechanical and
(a) For Mechanical Functions (Fixation, Support etc.):
i. Prop Roots:
These roots are developed from the horizontal branches of some trees in vertically downward direction. On reaching the soil each root grows into thick and woody pillar-like structure which gives support to the branch from where it developed. These are found in Indian rubber (Ficus elastica) and banyan (Ficus benghalensis, Fig. A) of Moraceae.
ii. Stilt Roots:
These are stout roots developed obliquely from the lower part of the trunk; grows on soft soil. On reaching the soil they help the mother plant to keep erect and also give an additional anchorage support to prevent from being uprooted. These are found in screwpine (Pandanus foetida, Fig. B) of Pandanaceae; maize, sugarcane etc. of Poaceae.
iii. Root-Buttresses or Plank-Buttresses:
These are plank-like structures developed with the contribution of both stem and root, come out as erect projections from the basal region of the trunk. These plank-like structures are called root-buttresses or plank- buttresses (Fig. C). These are found in Bombax ceiba of Bombacaceae; Terminalia catappa of Combretaceae, Sterculia alata of Sterculiaceae etc.
iv. Climbing Roots:
These are the roots developed from the node of some weak plants and help to climb the host plant. The apices of these roots produce a viscous substance which is dried in the air and so the roots get themselves attached to the host plant. These are found in betel vine (Piper betel of Piperaceae, Fig. D), Pothos sp. of Araceae, etc.
v. Clinging Roots:
These are the short roots which, after developing from the stem, penetrate into the cracks and crevices of the supporting trees and help to fix the plant with the host plant. In addition to anchorage, they also absorb some food from the accumulating debris on the host plant. These are found in Vanda tesselata of Orchidaceae (Fig. A), Hedera helix of Araliaceae.
vi. Contractile or Pull Roots:
These are the roots found with the underground stems like rhizome, bulb, corm etc., along with other roots. These roots contract or swell so that the underground part or the aerial shoots are kept at a proper level in the soil. These roots are called Contractile or pull roots (Fig. B). This type of roots is found in Allium, Crocus, Canna, etc.
vii. Floating Roots:
These are small, inflated, spongy and white coloured roots developed adventitiously from the upper side on the node of the stem. These roots contain huge amount of air and help the plant to float on water; and also in respiration. These are found in Jussiaea repens of Onagraceae (Fig. C).
In some plants, adventitious roots developed from the base of the stem, being hard, pointed and thorn- like, are called root-thorns. As an armature they help the plant to protect itself from marauding animals. These are found in Polhos armatus (Fig. D) and in many palms like Iriartea and Acanthorhiza.
(b) For Physiological Functions (Storage of Food, Absorption of Moisture, Assimilation etc.).
For storage of Food-Matters:
i. Tuberous Roots:
These roots arise from nodes of the prostrate stem and become swollen irregularly without any definite shape. These are found in sweet potato, Ipomoea batatas of Convolvulaceae (Fig. A); Orchis maculata (Fig. B) of Orchidaceae etc.
ii. Nodulose Roots:
This type of roots, after coming out of the rhizome, becomes swollen at their apex as a nodule-like structure due to storage of food. It is found in mango-ginger (Curcuma amada) and Costus speciosus (Fig. C) of Zingiberaceae.
iii. Fasciculated Roots:
In this type, all the fibrous adventitious roots — after originating in cluster from a common point at the base of the stem — become swollen due to storage of food. It is found in Asparagus racemosus (Fig. D) of Liliaceae etc.
iv. Moniliform Roots:
In this type, roots are alternately swollen and constricted, thus they form a beaded structure. This is found in Dioscorea alata of Dioscoreaceae, Cyperus sp. of Cyperaceae (Fig. E), Vitis trifolia of Vitaceae etc.
v. Annulated Roots:
The roots look as if formed by several discs placed side by side. This is found in ipecac (Cephaelis ipecacuanha of Rubiaceae, Fig. F) — a medicinal plant found in the Himalayas.
For Absorbing Moisture from Air:
vi. Epiphytic Roots:
These are hanging aerial roots of epiphytic plants. The roots are covered by a thin greyish layer (4 -5 cell-layer in thickness) known as velamen. The velamen can absorb moisture from the atmosphere. It is found in orchid root (Vanda tesselata of Orchidaceae, Fig. A).
For Sucking Moisture from the Host:
vii. Parasitic Roots:
These are also called sucking roots or haustoria. The small root-like structure, after developing from the stem of the parasite, penetrates the tissue of the host plant and absorbs food.
These roots are found in dodder (Cuscuta reflexa of Convolvulaceae Fig. A, B), sandal wood (Santalum album of Santalaceae), Orobanche racemosa of Orobanchaceae etc.
viii. Assimilatory or Photosynthetic Roots:
Roots of some plants develop chlorophyll and become green. These roots are able to prepare carbohydrate foods through photosynthesis. These roots are found in Trapa sp. of Trapaceae (Fig. C), Tinospora cordifolia of Menispermaceae, Podostemon sp. of Podostemonaceae etc.
ix. Reproductive Roots:
Roots of some plants develop vegetative buds; those, after separating from the mother plant, produce new plants. These are found in sweet potato (Ipomoea batatus of Convolvulaceae, Fig. D); palwal (Trichosanthes dioica of Cucurbitaceae) etc.
x. Mycorrhizal Roots:
Roots of some plants get infested with fungal mycelium. The plants get their nutrition from humus soil, rich in organic substances, with the help of mycelia. These are mycorrhizal roots, occurring in many plants like Pinus sp. (Fig. E) of Pinaceae, Corallorhiza innata of Orchidaceae, Monotropa sp. of Pyrolaceae etc.
Root as a Dominating Plant Body:
In Podostemonaceae, the main plant body is a root, performing both assimilation and reproduction. This plant produces small flowering shoots from time to time. Podostemon (Fig. ) is a member of this family, found in Cherrapunji of Meghalaya (India).
Plants without Root:
Some angiospermic plants do not bear any root. Urticularia (Fig) , a submerged hydrophyte, has some finely dissected leaves which carry on the function of the root. Wolffia arrhiza, a very small angiosperm, does not have any root. Root is also absent in Epipogium.
Essay # 6. Functions of Roots:
The functions of roots are of two types.
A. Normal Functions:
a. Mechanical. Root helps in the fixation i.e., anchoring the plant with the substratum.
b. Physiological. Roots serve different physiological functions like:
i. Absorption of water containing various nutrients (sap) from the soil.
ii. Conduction of sap in upward direction.
iii. Storage of some amount of food in the permanent region.
B. Special Functions:
Besides the above normal functions, roots also carry some special functions of both mechanical and physiological types.
i. Support to the long horizontal branches, e.g., prop root of banyan (Ficus benghalensis).
ii. Clinging and climbing, e.g., orchid (clinging root) and betel vine (climbing root).
iii. Support and additional anchorage, e.g., stilt root of screwpine (Pandanus foetida).
iv. Protection, like root thorns of some palms.
i. Assimilation, e.g., assimilatory root of Trapa.
ii. Storage, e.g., storage root of sweet potato (Ipomoea batatas).
iii. Absorption of moisture from air, e.g., epiphytic root of orchid (Vanda tessellata).
iv. Sucking from host, e.g., haustoria of dodder (Cuscuta reflexa).
v. Breathing, e.g., pneumatophores of mangrove plants (Rhizophora mucronata).
vi. Reproduction, e.g., reproductive root of sweet potato (Ipomoea batatas).
Essay # 7. Economic Importance of Roots:
Economically, roots are very important to the mankind.
Some of the beneficial importance of the roots are:
1. Source of food for human being. Sweet potato, carrot, beet, turnip are the tuberous roots used as human food.
2. Source of sugar. Modified root like sugar beet is a source of sugar.
3. Source of medicine. Some roots have high quantity of active substances of great medicinal importance.
i. Ipecac from Cephaelis ipecacuanha of Rubiaceae,
ii. Aconite from Aconitum napellus of Ranunculaceae,
iii. Sarsaparilla from Smilax macrophylla of Liliaceae,
iv. Gentian from Gentiana lutea of Gentianaceae,
v. Liquorice from Clycyrrhiza glabra of Fabaceae,
vi. Rubarb from Rheum officinale of Polygonaceae.
4. Source of rubber. Root of Taraxacum koksaghyz of Asteraceae is a source of rubber.
5. Source of insecticide. Pyrethrum powder from Chrysanthemum cinerariafolium of Asteraceae is used as insecticide.