ROOTS
- Nodes and internodes absent
- Buds absent in roots
{present in sweet potato (Ipomea batata) and Indian rose wood (Dalbergia sisso also called as shisham)… These buds are called radical buds }
- Root cap is a protective single layer
*** root cap is multiple layered in screwpine ( Pandanus )
*** it is absent in hydrophytes as such but present as root pockets
Actually, root cap in form of loose sheaths is called as root pockets
Eg. Pistia, Eichhornia, Lemna
- Root hairs : elongations of some special epidermal cells called trichoblast cells (tricho in latin means hair, blast is used for parent cell, like fibroblast , erythroblast etc. )
- Epidermis of root : rhizodermis (rhizo means roots)
- Two types
- Tap root : root which arises from radical of seed. It is deep feeder and present in dicots(generally)
- Adventitious roots: made by any part other than radical eg. Stem, leaf etc. It is surface feeder and mostly present in monocots.
- Primary root= elongation of radical
- Secondary root = branches of primary root
- Tertiary root = branches of secondary root
- Rootlets = branches of tertiary root
Modifications…
Modifications of tap root
èFor storage
a) fusiform :
spindle shaped
eg. Radish (Raffanus sativus)
b) conical :
cone shaped
eg Carrot (Dauscus carota)
c) Tuberous:
eg 4’o clock plant (Mirabilis) \\ humorous common name naa??? I too laughed a lot at it when I had to study all these \\
d) Napiform:
Broad at one end, tapers at another end.
Eg: Turnip (Brassica rapa) eg2: Beet root (Beta vulgaris)
è Respiratory roots (pneumatophores): mangrove plants like Avicennia, Sonneritia
These help in gaseous exchange. And they are negatively (-ve) geotropic (anti gravitational movement. i.e move opposite to gravity )
è Nodulated roots
Rhizobium bacteria is present in the nodules
Eg. Legume plants.
Aerorhizobium present in Sesbania plant in which stem nodules are formed. In the same plant, rhizobium are also present in their root nodules.
Modifications of adventitious roots
è For storage
i) Tuberous
Eg. Sweet potato ( Ipomea batata)
ii) Fasciculated roots
*** Fascicula = group ( many group tubers present)
Eg Asparagus, Dahlia
iii) Palmate roots
*** Looks like palm of hand
Eg. Orchis
iv) Beaded roots ( monoliform roots)
*** swellings at regular intervals present
Eg. Vitis
v) Nodulose roots
*** swelling at one end of root
Eg. Mango ginger (Curcuma amanda)
v) Annulated roots
*** Ring like
Eg. Ipecac.
è for mechanical support
i) Prop roots
*** Pillar like
Eg. Banyan tree ( Ficus benghalensis) , Ficus genus in general
*** In banyan tree, these are hygroscopic in nature. It turns red on absorbing water
ii) Stilt roots / Brace roots
Originate from lower nodes of stem.
Obliquely enter the soil
Support complete stem
Eg. Jowar, Sugarcane etc. (most of the monocots)
iii) Butress roots / Plank roots
Originate from base of stem
Eg. Bamboo ( Bombax)
iv) Climbing roots
eg. Money plant (Pothos)
è Adventitious roots performing other special functions
i) Respiratory roots
Eg. Jussiaea
*** Not to be confused with pneumatophores which are modifications of tap root, but it too performs respiration.
ii) Assimilatory roots
*** Roots perform photosynthesis, make food.
Eg. Water chestnut (Trapa , also known as singhara in hindi)
Eg. Spring plant (Tinospora)
iii) Parasitic roots / Haustorial roots
Help in absorption of food and water from other plants
Haustoria enters vascular bundles of the host
Eg. Cuscuta
iv) Hygroscopic roots
Moisture absorbing roots
By help of dead hygroscopic tissue called velamen
Eg. Orchid
*** Velamen has multiple epidermis (usually, only single epidermal layer is present)
v) Nest roots
Nest à Modification of leaf
Humus rich soil present in nest.
Adventitious roots enter into nest called nest root
Absorption of water and minerals takes place
Eg. Dischidia rafflesiana
vi) Foliar roots
Developed from leaves
Eg Bigonia (for balancing)
è Buyashacka!!!!
i) Utricularia, Podostemon and epipogium have no roots
ii) Flowering roots are present in monotrapa
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