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CHAPTER-II              MORPHOLOGY OF ANGIOSPERMS

Morphology is the branch of biological science that deals with the study of form, size, colour, structure and relative position of various parts of organisms.

Importance of morphology.

a. Knowledge of morphology is essential for recognition or identification of plants.

b. It gives information about the range of variations found in a species.

c. Deficiency and toxicity symptoms are morphological changes that occur in response to shortage or excess of minerals.

Parts of Flowering Plants-

All the flowering plants have roots, stem, leaves, flower and fruits. The underground parts of flowering plant are the root system and the portion above the ground forms the shoot system.

THE ROOT

 In Dicotyledons, elongation of radicle forms the primary roots which bears lateral roots of several orders called secondary roots, tertiary roots etc. primary roots along with lateral roots forms the Tap root system. In monocotyledons, primary root is replaced by large number of roots at its base of stem to constitute the Fibrous root system (Wheat, rice etc).

The roots that arise from other parts of plant beside radicle are called adventitious roots. Example- Grass, Banyan tree, Maize, onion etc.

The main function of root system are absorption of water and minerals from soil, providing proper anchorage to the plant parts and storing reserve food materials.

Some roots provide additional mechanical support (prop roots of banyan, stilt roots of maize). Some store food e.g carrot, radish, potato etc.

Regions of Roots-

The apex of root is covered by a cap like structure called root cap, it protect the tender apex of root while making way through soil.

Above the root cap is region of meristematic activity having small cells with dense cytoplasm.

The cells above the region of meristematic activity is region of elongation where cells undergo elongation and enlargement to increase the length of root.

Root hair zone is characterized by elongation of epidermal cells (trichoblasts) forming root hairs (pilus). The root hairs enhance the exposed surface area of root.

Region of maturation contain the mature cells that do not undergo further division or change. Lateral roots arise endogeneously from the interior of this zone.

MODIFICATION OF TAP ROOTS-

Roots are modified for storage, nitrogen fixation, aeration and support.

Storage roots;-

Tap root of carrot, turnip and radish get swollen to store food. The storage roots usually swollen and assume various forms e.g conical in carrot (daucus carota), fusiform in radish (raphanus sativus), napiform in turnip (brasica napas).

Nodulated roots;- In leguminous plants like pea gram, beans etc the primary tap root and its branches bear nodules that cantain nitrogen fixing bacteria which fix atmospheric nitrogen.

Respiratory roots;- The roots of mangrove plants and halophytes develop numerous upright aerial branches called pnumatophores which bear small pores for gaseous exchange called lenticels or pneumatothodes.

 

MODIFICATION OF ADVENTITIOUS ROOTS;-

The adventitious roots are modified

 1.) For storage of food like tuberous roots of sweet potato (swollen)-E, fasciculted roots of asparagus (clustered swollen)-A, palmate tuberous roots of orchids (hand like), nodulose (not nodulated) roots of mango-ginger and cosus (swellowed at apex).

 2.) To give additional mechanical support:- like prop roots of banyan tree (ficus bengalensis) (grow vertically downward from branches and assume shape of pillars), stilt roots (brace roots) of maize sugar cane (arise from base and grow obliquely downwords), climbing roots of piper betel and ivy (twine round support and help in climbing).

3.) to perform vital functions like the photosynthetic roots of tinospora, podostemon, trapa, houstorial (parasitic) roots of viscum, epiphytic roots of dendrobium (these contain special tissue called velamen to absorb moisture), reproductive roots of sweet potato dahlia-E etc.

Some plants like wollfia arhiza and epipogium are root less.