Morphology of Flowering Plants

Stem


  • Stem is ascending cylindrical axis of plant body which develops from the plumule of embryo and grows by means of terminal bud
  • Stem branches are exogenous in origin.
  • Bud is a condensed, undeveloped, compact, embryonic shoot having a growing point covered with a gowded overlapping in mature leaves.
  • According to nature bud are classified into vegetative, floral and mixed buds.
  • On the basis of position buds are of 2 types (i) Terminal buds and (ii) lateral buds. [both axillary, accessory buds]
  • Active and dormant are the two types of buds on the activity.
  • Buds are modified into following ways
    (i) Bulbils Eg : Agave, onion
    (ii) Apical bud : Eg : Cabbage
    (iii) Turions : Hydrophytes
    (iv) Tendrils : Cucurbita, passiflora 
    (v) Thorns : Duranta
  • Unbranched stem is called caudex (Eg : palm)
  • Culm is that caudex in which nodes and inter nodes are well district Eg : Bamboo
  • Branching is of 2 types : (i) Dichotonomous (Eg : liverworts, Dictyota) and (ii) lateral (Eg : Eucalyptus, Polyalthia, mustard, viscus, Croton).
  • Stem is of 3 forms : (i) Aerial (ii) Sub aerial and (iii) Underground
  • Aerial / Epiterranean stem is above the ground which is of 3 types (1) Reduced (2) Erect and (3) Weak
  • Reduced : Eg : Radish, Carrot, Turnip, Lemna, Wolfia.
  • Twiners (Eg : Convolvulus, Ipomoea, Bean, Asparagus) and climbers are the 2 types of weak type.
  • The weak stem plants rise up with the help of some clinging (or) coiling structures which has 3 different types.
    (i) Tendril climbers (eg : root and stem climbers)
  • The weak stems take the support of ground for spreading which is of 4 types.

    (Eg : Tribulus, evolvulus) (Eg : Tridase, Portulaca)
  • Runners : Eg : Oxalis, lawn grass, centella
  • Stolons : They may be above the ground (Eg : Strawberry) (or) Underground (Eg : Colocosia)
  • Offsets are one internode long thicke, short runners formed in rosette plants at ground or water level. Eg : Water lettuce (Pistia) and Eichornia
  • Sucker (Eg : Chrysanthemum, mint) [Banana possess sword suckers]; Rhizome (eg : ginger, Turmeric, canna, Banana, Avoids); Corm (Eg : Amorphophallus, Colocossia, Fresia, Colchicum and Gladiolus); Bulb (Simple tunicated bulb - onion ; compound Tunicated bulb - Garlic : Scaly bulb ; lily): (Tubers, potato, Helianthus, Stachys)
  • Each tuber has a number of eyes (nodes) and 3 buds and therefore eye represents node and axillary buds. Eyes are more towards distal and where terminal bud is present and then end is called rose end.
  • The skin has corky covering with tentacles : Eye represent seed of a plant.
  • Aerial stem modification by providing support and protection.
  • Stem tendrils (Eg : Passiflora, Cucurbita, Antigonon)
  • Stem thorns (Eg : Citrus, Pomegranate, Bougainvillea)
  • Phylloclades are green, photosynthetic, often succulent stems of indefinite growth which is an adaptation to dry habitats (Eg : Euphorbia, opuntia, casuarina)
  • Cladodes (Cladophylls) are green stems of limited growth. (Eg : Ruscus, Asparagus, Lemna)

View this video for the topic from 16:36 to 26:04

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