Objective. To identify and comment upon the specimens of root modifications.

 EXPERIMENT 7.1

INTRODUCTION

1.Different plant parts perform different functions. For example roots fix the plant in the soil and absorb water and minerals from the soil ; stem supports the branches, leaves, flowers and fruits and also conduct water and food to different parts ; leave synthesis food and facilitate exchange of carbon dioxide and oxygen.

2.In some cases the plant parts perform functions other than the normal ones and, thus, their morphology is also changed accordingly. Such plant parts are called modified organs.

3 In other works, the organs that perform specialized functions are called modified organs.

Objective. To identify and comment upon the specimens of root modifications.

REQUIREMENTS Fresh or preserved specimens of modified roots, practical note book, pencil, eraser, etc.

PROCEDURE

1.Observe the specimen carefully and note down its special features.

2.Draw the specimen on the practical note book. Depict only the parts actually visible in the specimen.

3.Write down the morphological features and the features of special interest of the specimen.

OBSERVATIONS AND COMMENTS

1. CARROT ROOT

Comments

MODIFICATIONS OF TAP ROOTS

Identification. Conical, fleshy tap root of Carrot Daucus carota).

(1) It is thick at the base and gradually become thin towards apex, resembling a cone.

2.The stem is reduced, discoid and bears radical leaves.

(iii) The root is fleshy due to storage of food.

(iv) Many thread like secondary roots are present throughout the length of the root.

2. RADISH ROOT (EUROPEAN RADISH)

Identification. Fusiform fleshy tap root of Radish (Raphanus sativus).

Comments

(i) It is spindle shaped, that is, thickest in the middle and narrow towards both its base and apex.

(ii) The basal and middle fleshy part of the root is formed by hypocotyl.

(iii) The stem is reduced, discoid and bears radical roots.

(iv) Many thin thread like secondary roots arise throughout the length of the root.

(v) The root is fleshy due to storage of food.

3. TURNIP ROOT/BEET ROOT

Identification. Napiform, fleshy tap root of Turnip (Brassica rapa)/Beet (Beta vulgaris).

Comments

(i) It is almost spherical at the base abruptly tapering towards the apex, looking like a top or pitcher.

Ii. Most of the swollen part in hypocotyl, the tap root occurs only towards the narrow pointed apical region.

(iii) The stem is reduced, discoid and bears radical roots.

(iv) The narrow pointed apical region bears thin thread like secondary roots.

(v) The root is fleshy due to storage of food.

4. ROOTS OF FOUR O'CLOCK PLANT

Identification. Tuberous, fleshy tap roots of Four O'clock plant (Mirabilus jalapa).

Comments

(i) It is a thickened tap root, which does not have a definite shape.

(ii) The root is fleshy due to storage of food.

(iii) It bears a number of thin thread like secondary roots.

5. ROOTS OF A LEGUME PLANT

Identification. Nodulated (Tuberculate) roots of a leguminous plant.

Comments

(i) There are present numerous small or large irregular swellings called root nodules or tubercles on the secondary ,tertiary or sometimes the primary roots.

(ii) The root nodules contain nitrogen fixing bacteria(Rhizobium), which fix the atmospheric nitrogen into organic compounds of nitrogen.

(iii) The roots, help in nitrogen fixation and thus, improve the fertility of soil.

6. ROOTS OF A MANGROOVE PLANT

Identification. Respiratory roots (Pneumatophores) of a mangroove plant.

Comments

(i) These roots are found in plants growing in mangroves or saline swamps near the sea shore. e.g., Avicenia, Sonneratia etc.

(ii) There arise small peg like upright aerials or pneumatophores at short intervals from the horizontal roots.

(iii) The pneumatophores bear small pores called lenticels or pneumatic for exchange of gases.

1. SWEET POTATO

MODIFICATIONS OF ADVENTITIOUS ROOTS

Identification. Tuberous fleshy adventitious root of Sweet potato (Ipomea batatas).

Comments

(i) It is a swollen root having irregular shape.

(ii) It is an adventitious root as it arises from prostrate stem of sweet potato plant.

(iii) It is fleshy due to storage of food. 

(iv) It bears adventitious buds and hence, help in vegetative propagation.

2. ROOTS OF DAHLIA/ASPARAGUS

Identification. Fasciculated roots of Dahlia Asparagus.

Comments

(i) These are swollen roots which arise in clusters. In Dahlia they lie at the base of the stem, while in Asparagus clustered roots become fleshy at intervals and not exactly at the base.

(ii) The roots are adventitious as they arise from the base of the stem.

(iii) The roots are fleshy due to storage of food.

3. ROOTS OF BANYAN TREE

Identification. Prop or Pillar roots of Banyan tree (Ficus bengalensis).88

Comments

(i) These are thick pillar like adventitious roots which grow from heavy horizontal branches of Banyan tree and give support to them.

(ii) Initially, the roots are aerial and hygroscopic, and become thick and pillar like, when they reach the soil.

4. ROOTS OF SUGARCANE/MAIZE/SORGHUM

Identification. Stilt roots of Sugarcane/Maize Sorghum.

Comments

(i) These are short but thick supporting roots which develop obliquely from the basal nodes of the stem.

(ii) They usually grow in whorls around the nodes.

(iii) After penetrating the soil, they provide support to the long and narrow jointed and unbranched stems (calms)like the ropes of pole.

5. ROOTS OF WATER NUT (Trapa)/Tinospora

Identification. Assimilatory roots of Water nut (Trapa)/Tinospora.

Comments

(i) These are green roots which arise from the stem and are capable of photosynthesis.

(ii) In Trapa, the green assimilatory roots are finely dissected and are submerged like other roots. While, in Tinospora, the green assimilatory roots arise from the stem nodes during the rainy seasons and shrivel during drought.

(iii) Assimilatory roots increase photosynthetic area of the plant.

6. ROOTS OF DODDAR (Cuscuta)

Identification. Haustorial or Parasitic roots of Doddar (Cuscuta).

Comments

(1)These are fine spine like roots which arise from the stem of Cuscuta plant and penetrate into the host plant.

(ii) These roots absorb nourishment from the host plant, as the parasitic plant is non-green and can not prepare its own food.

(ii) These roots make connections with both xylem and phloem of the host and absorb both water and food, hence, they are also called sucking roots.

7. ROOTS OF MONEY PLANT (Pothos)/Tecoma/Ivy/Betal (Piper betal)

Identification. Clinging or Climbing roots of Money Plant(Pothos)/ Tecomal Ivy/Betal.

Comments

(i) These are non absorptive adventitious roots which arise from the nodes (in Tecoma, Pothos/Betal), or both from nodes and inter nodes (in Ivy).

(ii) They penetrate the cracks or fissures of the support or stick to the support.

(iii) These roots help the plant in climbing over the support.

8. ROOTS OF VANDA (An Epiphyte)

Identification. Hygroscopic or Epiphytic roots of Vanda (An Epiphyte).

Comments

(i) These roots are formed in epiphytic plants such as Vanda.An epiphyte possesses three types of roots: clinging (for fixation) absorbing (for absorbing minerals) and hygroscopic (for absorbing water).

(iii) The hygroscopic roots are thick and hang down in the air.

(iv) These roots possess a covering of dead spongy tissue called velamen, which helps the roots to absorb water from moist atmosphere, dew and rain.

9. ROOTS OF JUSSIAEA

Identification. Floating Roots or Root floats of Jussiaea (A hydrophyte).

Comments

(i) These are adventitious roots which arise from the nodes of stem of Jussiaea (a hydrophyte).

(ii) Some of them store air, become inflated and project out of water and function as float.

(iii) The floating roots help the plant in floating on the surface of water and also in gaseous exchange.