2. ROOTS
• Roots unlike stems lack nodes and
internodes, have irregular branching and
produce endogenous lateral roots.
• Upon seed germination, usually the radicle
elongates into a primary root, forming a
taproot, but several other variations may be
encountered:
3. • Adventitious: Developing from any part other than radicle or another
root.
• Aerial: Grows in air. In epiphytes, the aerial roots termed epiphytic
roots are found hanging from the orchids and are covered with a
spongy velamen tissue. Orchids also carry some clinging roots which
penetrate crevices and help in anchorage.
• Assimilatory: Green chlorophyll-containing roots capable of carbon
assimilation as in Tinospora cordifolia, and many species of
Podostemaceae.
• Fibrous: Threadlike tough roots common in monocots, especially
grasses, usually adventitious in nature. Buttressed: enlarged,
horizontally spread and vertically thickened roots at the base of
certain trees of marshy areas.
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4. • Fleshy: Thick and soft with a lot of storage tissue.
Storage roots may be the modification of taproot:
(i) Fusifom: Swollen in the middle and tapering on sides, as in radish
(Raphanus sativus).
(ii) Conical: Broadest on top and gradually narrowed below, as in carrot
(Daucus carota).
(iii) Napiform: Highly swollen and almost globose and abruptly narrowed
below, as in turnip (Brassica rapa).
Modifications of the storage adventitious roots include:
(i) Tuberous : Clusters of tubers growing out from stem nodes, as in sweet
potato (Ipomoea batatas) and tapioca (Manihot esculenta).
(ii) Fasciculated : Swollen roots occurring in clusters, as in Asparagus and
some species of Dahlia.
(iii) Nodulose : Only the apices of adventitious roots becoming swollen like
beads, as in Curcuma amada and Costus speciosus.
(iv) Moniliform : Portions of a root are alternately swollen and constricted giving
beaded appearance, as in Dioscorea alata
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5. • Haustorial (sucking): Small roots penetrating the host xylem
tissue for absorbing water and nutrients as in partial parasites
(Viscum) or also the photosynthetic materials by penetrating the
phloem tissue as well, as in total parasites (Cuscuta).
• Mycorrhizal: Roots infested with fungal mycelium which helps in
root absorption. The fungal mycelium may penetrate cortical cells
(endotrophic mycorrhizae found in orchids) or may largely form a
mantle over the root with a few hyphae penetrating between the
outer cells (ectotrophic mycorrhizae found in conifers). In
specialized VAM (vesicular arbuscular mycorrhizae) found in
grasses, the fungal hyphae penetrate cortical cells, forming a
hyphal mass called arbusculum.
• Respiratory: Negatively geotropic roots of some mangroves (e.g.
Avicennia) which grow vertically up and carry specialized lenticels
(pneumathodes) with pores for gaseous exchange. Such roots
are also known as pneumatophores.
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6. • Prop: Elongated aerial roots arising from horizontal branches
of a tree, striking the ground and providing increased
anchorage and often replacing the main trunk as in several
species of Ficus (e.g. the great banyan tree F. benghalensis in
the Indian Botanical Garden at Sibpur, Kolkata). The large
hanging prop roots of Ficus species are often used in bungee
jumping sport.
• Stilt: Adventitious roots arising from the lower nodes of the
plant and penetrating the soil in order to give increased
anchorage as in maize (Zea mays), screw-pines (Pandanus)
and Rhizophora.
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