MORPHOLOGY OF ANGIOSPERMS: ROOT

General Introduction

· Angiosperm is the most advanced, most evolved spermatophyte.
· Angiosperm is the highly evolved plant group developed in the cretaceous period of the Mesozoic era.
· Sporophytic body of the angiosperm can be divided into root, stem and leaf.

· Angiosperms can be divided into two categories based on the number of cotyledons in their seed.
(a) Monocots

(b) Dicots based

· Vascular tissue xylem and phloem are well developed.

· Xylem is represented by vessels, while phloem possesses companion cells and sieve tubes.

Morphology

· (Morphe = form + logos = study)

· It deals with the forms and features of different plant parts.
· The main plant body is differentiated into
(a) Root system: Roots, Root hairs.
(b) Shoot system: Stem, leaves, flowers, etc.
· Carolos Linnaeus is considered the father of morphology.
· Root, stem, and leaves are the vegetative part.
· Flower is the Reproductive part.

· Theophrastus classified plants into Herbs, Shrubs and Tree.
A. Herbs

· Usually small with a soft delicate and green stems.

· They may be either annual or biennial or perennial
E.g. Mustard (Brassica campestris)
· Annual – Completes life cycle within one season or one year. e.g. Paddy, wheat
· Biennial – Completes their life cycle in two years. e.g. carrot, radish, turnip.
· Perennial – completes their life cycle in more than two seasons or year.

B. Shrubs

· Bushy type of plants, which are usually taller than herbs.
· Stem is divided into branches and sub-branches.

E.g. Perennials (China rose, Rose) etc.

C. Trees

· Much taller than herbs or shrubs.
· Develops a hard woody and repeatedly branched stem.

· They are perennial.

E.g. Pine, Mango, Ficus etc.

D. Monocarpic plants

· The plants which bear flowers and fruits only once in their life.

E.g. bamboo, Agave (Century plant) etc.

E. Polycarpic plants

· The plants which after attaining maturity bear flowers and fruits repeatedly usually every year.

E.g. Mango

F. Shrines

· These are the plants having medium height, perennial habit and woody stem without any distinct truck.

G. Cryophyte plants

· Plants growing at lower temperatures.

ROOT

· Roots is underground, the positively geotropic non-green structure of the plant.
· It is the underground system, which is below the soil and originates from the radicle of the embryo.
· They anchor the plant where it is growing and absorb water and minerals salt from the soil.
· Root lacks distinct nodes, internodes, buds, and leaves.
· Basal portion of the root has a cap-like structure called root cap.
· Multiple root cap is found in Pandanus (screw pine)
· Root cap is absent in Hydrophytes (aquatic plants)
· A finger-like projection called a root pocket is found in aquatic plants, like Pistia, Eicchornia, Trapa.
· Root hairs are totally absent in aquatic plants.
· Mycorrhizal roots (symbiotic association between algae and fungi) occurs in the root of higher gymnosperms like pine
· Parasitic roots (Haustorial roots) completely lack root hairs.
· Roots don't have leaves, nodes and internodes.

A. Characteristics of Root
1. Root is the descending part, direct prolongation of the radicle. (whereas shoot system– prolongation of plumule.)
2. Root bears unicellular hairs, while the stem or the scoot bears mostly multicellular roots.
3. Root doesn't normally bear bud while steam bears buds.
4. Lateral roots are endogenous in origin. (leaves of plants are exogenous in nature.)
5. Nodes and internodes in roots are always absent.
6. The root ends in and is protected by a cap or thimble known as a root cap.
· In certain aquatic plants like duckweed (Lemna), Water lettuce (Pistia) etc. root cap or root pocket is present.
7. Root bears unicellular hairs and stem bears multicellular wire.

B. Region of the Roots
1. Root cap:

· Each root is covered at the apex by a sort of a cap or thimble known as the root cap.

· The root cap covers the underlying dividing meristematic tissues.
· Usually absent in aquatic plants and multiple root cap is common in screw pine (pandanus).
· Its mucilaginous secretion helps in lubrication.

2. Region of Cells Division
· Growing apex of the root lying within and little beyond the root-cap.
· The cells of this region undergo repeated division.

3. Region of Cell Elongation
· Lies above the meristematic region.
· Undergo rapid elongation and enlargement
· Responsible for the growth in the length of the root.

4. Region of Maturation or Root Hair Zone
· This region lies above the region of elongation.
· This region produces a cluster of very fine and delicate thread-like structures known as root hairs.
· Above the root hair zone, it produces lateral roots.
· They help to absorb water and mineral salts from the soil.
. Lateral roots arise from the pericycle, which is endogenous in nature.
· Root hairs and leaves are exogenous in nature.
· Dividing tissues are present in the sub-terminal part of roots.

Primary root – Roots that are directly originating from the radicle of the embryo.
Secondary root - Arises from Primary root.
Tertiary roots – Arises from Secondary roots.
· Rootlets arise from the tertiary roots.

Fig: L.S of Root Tip

1. Taproot system

· Origin – Radicle of embryo
· Common in dicots.
· Positively geotropic and negatively phototropic.
· Arises directly from the radicle of the embryo.
· Primary root continues to grow and remain distinct.

· Primary root gives off lateral roots that grow outward and downward. It persists throughout the life of the plant. e.g. Carrot, Turnip etc.

A. Various Modifications of Taproot:
1. Fleshy taproot or Storage Taproots

· Some taproots are fleshy due to the storage of food materials.
· According to the shape, they are classified as.
a. Fusiform (Spindle like):

· Swollen root tapering at both the ends at the base as well as at the apex, forming more or less spindle-like structures.

E.g. Radish

b. Napiform:

· The root is considerably swollen at the upper part becoming almost spherical and sharply tapering at the lower part.

E.g. Turnip (Brassica rapa) and Beet.

c. Conical:

· Root is broad at the base and it gradually tapers towards the apex like a cone.

E.g. Carrot

d. Tuberous or Tubercular root:
· Root is thick and fleshy but does not maintain any particular shape.
· Irregular type of swelling. e.g. Mirabilis Jalapa (4 o'clock plant)

e. Pneumatopores or Respiratory roots
· Respiratory root common in plants growing in salty habitat (halophytes)
· They have many aerating pores called breathing pores (Pneumathode).
· They are negatively geotropic or apogeotropic and common in mangrove plants.

E.g Sonneratia, Rhizophora

Fig: Fleshy Tap Roots

2. Adventitious Roots
· Roots that grow from any other part of the plant other than the radicle
· Maybe underground or aerial.
· They develop from
   1. Node and internodes
   e.g. Sugarcane and Bamboo.
   2. Underground stem
   e.g. Rhizomes, Bulbs or Corms.
   3. Base of the stem
   e.g. Fibrous roots in monocot.

Fig: Tap and Adventitious root systems

B. Modification of Adventitious roots
A. For storage.
a. Tuberous or Tuberculated Root

· Swollen root without any definite shape.

E.g. sweet potato.

b. Fasciculated Root

· Several tubercular roots occur in clusters at the base of the stem.

E.g. Dahlia, Asparagus

c. Beaded or Moniliform Root

· Several swellings in the root at frequent intervals.

E.g. Momordica charantia

d. Nodulose Root:

· The shander roots swells suddenly at its tip for storage of food.
e.g. Turmeric (Curcuma domestica)

e. Annulated Root:
· Root has a ring-like swelling on its body.

E.g. Cephaelis, Ipecac (Psychotria)

B. For mechanical support
a. Fibrous Root:

· Threadlike roots at the base of the stem.

E.g. Wheat, Rice

b. Prop roots or Pillar Root:
· Thick woody type of roots arises from the aerial branches of some trees, which provides mechanical support to the plant.

E.g. Banyan (Ficus benghalensis), Rhizophora

c. Stilt Root:
· Oblique roots arise from the basal node of some plants that give extra support to the plant.

E.g. Maize, Sugarcane (Saccharum officinarum), Bamboo (Bambusa vulgaris or dendrocalamus)

d. Climbing Root:
· Roots arise from the nodes and help the plant in climbing.
· The apices of these roots produce a viscous substance, which dries up in the air so that the roots get fixed to the host plant.
e.g. Money plant (Pothos), Betel and Black pepper.

e. Clinging Roots
· Roots arise from the axils of leaves or nodes of the stem and pierce substratum plant to facilitate fixation.

E.g. Orchids

f. Haustoria or Parasitic Root
· Parasites develop certain kinds of roots, which penetrate into the living tissue of the host plant and suck it. Such roots are known as sucking or haustoria.

E.g., Dodder (Cuscuta)

g. Epiphytic Roots
· These are aerial roots hanging from some epiphytic plants such as Orchids (Eg. vanda).

· These hanging roots do not draw nutrition but absorb moisture from the surrounding air with the help of a spongy tissue called velamen which is hygroscopic in nature.

· Epiphytes – a plant that grows on the big trees but does not absorb nutrition from it is rather attached to the big trees for support.

They develop 3-type of roots
   a. Clinging – for fixing
   b. Absorbing – for absorption
   c. Hygroscopic – for moisture absorption from the air by velamen tissue.

3. Nodulated root or Nodulase (Tuberculated roots)
· Slender roots becomes suddenly swollen at or near the Apex.
· Primary secondary and Tertiary roots of some dicot plant has root nodule.
E.g. Papilonaceae family
· Root nodule of Legume contains symbiotic nitrogen-fixing bacteria.

E.g. Rhizobium

3. Mycorrhizal Roots
· These are the roots of certain higher plants that occur in association with the fungal hyphae.
· It is a symbiotic relationship of fungi with the roots of higher plants and fungal partners.

E.g. Roots of plants like pinus and other gymnosperms.

4. Buttress Roots or Plank
· Thick woody type of roots arises from the base of the plant, which gives extra support to the plant.
E.g. Ficus religiosa (Peepal), Bombax ceiba (simal)

h. Assimilatory Roots or Photosynthetic Roots
· Long slander hanging roots that develop from the branches of certain plants. They have chlorophyll and carry out photosynthesis.

E.g. Trapa (water chest nut) Tinospora, Taeniophyllum (3T)

i. Floating Roots
· Soft, light, spongy, and colourless adventitious roots, which store up air.

· They are common in aquatic plants and help in floating.

E.g. Pistia, Echiornia etc.

j. Leaf root: Leaf modified into roots.
· Common in Bryophyllum, which reproduces by foliar buds (leaf buds).

E.g. Salvia.

k. Epiphyllous Roots
· Roots develop on the leaf.

l. Reproductive Roots
· The adventitious roots develop adventitious buds and help in vegetative propagation.
· Roots of some plants develop vegetative bud, which after separation from parent plant develops into a new plant.

E.g. sweet potato.

VVI Entrance Exam Tips!

· Total stem parasite: Cuscuta (Dodder)
· Partial stem parasite: Viscum
· Total root parasite: Rafflesia or Orobanche
· Partial root parasite: Santalum
· Smallest Angiosperm: Wolffia
· Tallest Angiosperm: Eucolaptus regnans
· Smallest seed: Orchid
· Largest seed: Lodoicea.

High Yeilding Points from ROOT

A. ROOTS:

1. Total root parasites: Balanophora, Rafflesia, Orobanche (@ BARAK OBAMA)

2. Partial root parasite: Santalum, Thesium (@ ST.PR)

3. Total stem parasite: Cuscuta

4. Partial stem parasite: Loranthus, Viscum (@ LOVI PARAS)

5. Climbing roots are found in VIP PAN @ V = IVY

P = POTHOS (MONEY PLANT)
PAN = PIPER BETEL

6. Stilt roots are found in Screwpine, Maize, Sugarcane (@ SMS)

7. Food storage Taproot: Napiform (Turnip), Fusiform (Raddish), Tuberous (Mirabilis).

8. Food storage Adventitious roots: Tuberus (I. batata) Fasciculated, Palmate (Oriza) Nodulose (Ginger), Moniliform (Momordica)

9. Fasciculated roots are found in Dahlia, Aspergillus (@ FAD)

10. Plantless root: Podostemon, Archeuthobium, Rafflesia, Sapari, Monotrapa (@ PARASMANI)

11. Rootless plant: Balanophora, Utricularia, Ceratophyllum, Cuscuta, Wolffia (@ BAU KO CECUWA)

Also, Read Notes of other Lesson of Botany: