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STRUCTURAL ORGANISATION IN PLANTS 3 11th|I PUC NEET|BIOLOGY:VOL-II MORPHOLOGY OF FLOWERING PLANTS 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 Tertiary roots secondary roots lateral roots Region of meristamatic activity Region of maturation Root cap Root hair Region of elongation Tap root system Fibrous root system The regions of the root 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) 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 (Raphanus sativus) ii) Conical roots - These roots are thicker at their upper side and tapering at lower side eg. Carrot (Daucus) iii) Napiform roots - These roots become swollen and spherical at upper end and tapering (like a thread) at their lower end. Eg. Turnip (Brassica rapa), Sugarbeet = Beet root (Beta vulgaris)
4 STRUCTURAL ORGANISATION IN PLANTS 11th|I PUC NEET|BIOLOGY:VOL-II iv)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 Fusiform Conical Napiform Tuberous Nodulated roots 2. Tap root modified 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 pneu- matophores 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) Breathing pores Pneumato phore Mangrove plant Pneumatophore Normal root (A) (B) Pneumatophores (A) Plants showing pneumatophores (B) Part of pneumatophores showing breathing pores 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 after a regular interval. Eg. Vitis(Grapes), Momordica (Bittergourd), 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 batatus) 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).
STRUCTURAL ORGANISATION IN PLANTS 5 11th|I PUC NEET|BIOLOGY:VOL-II v) Prop roots or pillar roots - These roots arise from branches of plant and grow downward towards the soil. These roots support the tree. Eg. Banyan (Ficus bengalensis) Fasciculated roots Beaded or Moniliform roots Tuberous roots Stilts roots 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. ix) Annulated roots : In these roots swelling occurs in a series of rings on the roots. Eg. Ipecac. columnar roots of banyan Prop roots Climbing roots Adventitious leaf buds Leaf Foliar roots Annulated roots STEM Stem develops from the plumule of the embryo of a germinating seed. The stem bears nodes and internodes. The region of the stem where leaves are born are called nodes while the portions between two nodes are called internodes. Stem shows negatively geotropic growth.
6 STRUCTURAL ORGANISATION IN PLANTS 11th|I PUC NEET|BIOLOGY:VOL-II The main function of the stem is spreading out branches bearing leaves, flowers and fruits. It conducts water, minerals and photosynthates (food). Some stems perform the function of storage of food, sup- port, protection and of vegetative propagation. Forms of stem i) Caudex/Columnar : It is unbranched, erect, cylindrical stem and marked with scars of fallen leaves. eg. Palm. ii) Culm : Jointed stem with solid nodes & hollow internodes. eg Bamboo (Gramineae). Modification of stem A - sub-aerial modification - These are creeping stems. 1) Runner - In these stems roots develop at lower side and leaves at upper side from the nodes eg. Cynodon dactylon (Doob grass), Oxalis. 2) Stolon - In it branches develop from the lower part of the main stem and grow for some distance like arch and finally touch the ground to give rise to new shoot. Eg. Fragaria (Wild strawberry), Jasmine, Peppermint 3) Sucker - In it the main stem grows in the soil but branches develop from nodes and comesout from the soil. Eg. Mint, Pineapple, Chrysanthemum, Banana. 4) Offset - Generally these occur in aquatic plants which have fragile stem. Intemodes of offset are small & thicker and each node bears a rosette of leaves and a tuft of roots. It is also known as aquatic runner. Eg. Pistia, Eichhornia Runner Stolon Sucker Offset Leaves Aerial Shoot Scale Leaf Suckers Adventitious Roors Stolon Leaflets Scale Leaf Terminal Bud Roots Offset Leaves Adventitious Roors B - Underground modification This type of modification occurs generally for food storage and vegetative propagation. 1) Tuber - The tips of branches become swollen in the soil. Eyes are found on tuber which are axillary buds and axillary buds are covered with scaly leaves. Eg. Potato. 2) Rhizome - It is fleshy stem which grows horizontally in the soil. Nodes and small intemodes are found which are covered by scaly leaves. Eg. Ginger, Turmeric, Canna, Water lily, Banana. 3) Corm - It is condensed structure which grows vertically under the soil surface. Eg.Colocasia, Zaminkand, Saffron, Colchicum.