ROOT

Roots are (+) vely geotropic. (+) vely hydrotropic. (-) vely phototropic.

TYPES OF ROOTS :

Tap roots - In most of the dicot plants, the direct elongation of the radicle leads to the formation of primary root It bears lateral roots of several orders that are referred to as secondary. tertiary roots, etc.

The primary roots and its branches constitute the tap root system. Eg. : mustard plant

Adventitious roots :- In some plants, like grass, Monstera and the banyan tree roots develop from parts of the plant other than the radicle and are known as adventitious roots.

Fibrous roots :- In monocot plants, the primary root is short lived and.is replaced by a large number of roots. These roots originate from the base of the stem and constitute the fibrous root system. Eg.: wheat plant.

Functions of the root system - Absorption of water and minerals, provide a proper anchorage to the plant parts, storage of reserve food material (Carrot, radish, turnip sweet potato and Asparagus and synthesis of PGR (plant growth regulators).

MODIFIED ROOTS

1. Modified tap root for storage :

(i) Fusiform roots/Spindle roots These root are thicker in the middle and tapering on both ends.

eg. - Radish

(ii) Conical roots These roots are thicker at their upper side and tapering at lower side eg. Carrot

(iii) Napiform roots These roots become swollen and spherical at upper end and tapering (like a thread) at their lower end. Eg. Turnip sugarheet - beetroot Beta vulgaris

(vi) Tuberous roots - These roots do not have regular shape and any portion of roots become swollen & fleshy. Eg. Mirabilis.

(v) Nodulated roots - Nodules are formed on branches of roots by nitrogen fixing bacteria (Rhizobium

Eg. Plants of Papilionatae sub family of leguminosae family - Pea, gram, bean

2. Tap root modification for respiration

 In marshy/swampy areas, scarcity of OXYgen is found. Some branches of tap root of the plants which grow in this region grow vertically upward and comes on the surface These roots are called pneumatophores which have minute pores called pneumathodes or lenticels by which air enters in the plant and plant gets oxygen for respiration Pneumatophores are negatively geotropic. 

Eg. Rhizophora, Heritiera, (Mangrove plants)

Modification of adventitious roots :

(i) Fasciculated roots. These are adventitious roots occuring in clusters and all of them are swollen.

Eg Asparagus, dahlia

(ii) Beaded or moniliform roots - Root swells up like a bead at different places altes a regular interval.

Eg. Vitis(grapes), Momordica (bitter gourd, Portulaca.

(iii) Tuberous adventitious roots: The food is stored in these roots therefore they become swollen and irregular. These roots have no definite shape Eg. Sweet potato (Ipomoea batatas)

(iv) Stilt roots or brace roots - These roots arise from lower node and enter in the soil. These roots are Supporting roots. Eg. Maize, sugarcane. Pandanus (screwpine).

(v) Prop roots or pillar roots. These hanging roots arise from branches of plant and gmw downward forwards the soil. These roots support the tree. Eg. Banyan (Ficus benghalensis)

(vi) Climbing roots - These roots arise from nodes and help in climbing. Eg.Money plant (Pothos), Monstera, betel (Piper betel, black pepper

(vii) Foliar roots or Epiphyllous roots :- When roots arise from leaf then they are called foliar roots.

Eg. Bryophyllum, Begonia.

(viii) Sucking roots or Haustorial roots or Parasitic roots :- In parasitic plants, roots enter in the host plant to absorb nutrition from the host. Eg. Dendrophthoe, Cuscuta. Viscum.

(x) Annulated roots : In these roots swelling occurs in a series of rings on the roots. Eg. Ipecac.

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