Morphology of Flowering Plant: The Stem

  • The body of a typical flowering plant can be divided into the underground root system and aerial shoot system. The shoot system is heterogeneous. Shoot system (stem) is an aerial and erect part of plant body which grows upwards. It is usually above the soil and develops from plumule of the embryo of a germinating seed. It consists of stem, branches, leaves, flowers, fruits and seeds.
  • The stem is negatively geotropic (moves above the soil), negatively hydrotropic (moves away from the water) and positively phototropic (moves towards the light). 
  • Branches arise from axillary buds present in the axil of leaves. Each axillary bud is a small, compact, underdeveloped shoot covered with a large number of overlapping leaf primordia. Internodes of this bud enlarge and develop into a branch. Therefore the development of branches is exogenous (exo = outside).

Characteristics of Stem:

  • The shoot system is heterogeneous and consists of stem, branches, leaves and flowers.
  • The stem is negatively geotropic (moves above the soil), negatively hydrotropic (moves away from the water) and positively phototropic (moves towards the light). 
  • The stem bears nodes and internodes. The regions of the stem where leaves are born are called nodes while internodes are the portions between two nodes.
  • Stem bears vegetative buds which could be terminal (apical bud) for the plant to grow upwards or axillary (bud in the axil of leaf) which give rise to lateral branches. Stem bears floral buds (terminal or axillary) that grow into flowers
  • The young stem is green in colour and thus it is photosynthetic. The mature stem is generally green when young and later often become woody and dark brown.
  • Stem arises as a prolongation of plumule (one end of an embryo).
  • Lateral branches of the stem are exogenous in origin.

Functions of the Stem:

Primary Functions:

  • To support and orient the leaves in a manner that they are exposed to maximum sunlight and for efficient gaseous exchange during photosynthesis and respiration.
  • To conduct water and minerals from roots to leaves and manufactured food from leaves to different parts of the plant.
  • To bear flowers and fruits

Secondary Functions:

  • Some stems perform the function of storage of food, support, protection and of vegetative propagation.
  • Storage:  Some stems store food and water in some plants e.g. potato
  • Perennation: The underground stems help tide over the unfavourable growing periods e.g. ginger.
  • Vegetative propagation: e.g. rose, and sugarcane the stem can be used for vegetative propagation.
  • Photosynthesis: In xerophytes (desert plants) the leaves are reduced to thorn, the stem possessing chlorophyll takes up the function of photosynthesis. e.g.Opuntia
  • Protection: In some plants, the axillary bud modifies into thorn and protects the plants from grazing animals e.g. citrus, Duranta.
  • Support, Climbing and Clinging: Tendrils or hooks are modified branches or buds. They coil around
    the support and help the plant to climb e.g. grapevine.

Buds:

  • Small lateral or terminal protuberance on the stem of a vascular plant that may develop into a flower, leaf, or shoot is called bud. Buds arise from meristem tissues. Flower buds are modified leaves.

Types of Buds:

On the Basis of Their Function:

  • Vegetative buds: They contain embryonic leaves or shoots. They grow into new branches and shoots.

  • Floral buds: They contain embryonic flowers. They grow into flowers. They are also referred as reproductive buds.

  • Mixed buds: They contain both embryonic leaves and flowers. They may gro into vegetative parts like soot or leaf or into a flower part.

  • Tendrillar buds: They grow into tendrils.

On the Basis of Their Position:

  • Terminal or apical buds: They develop at the apex of main stem or branch. e,g, cabbage is large apical bud

  • Lateral buds: They develop into lateral branches or flowers. They are further classified as axillary buds, accessory buds and sub-petiolar buds. Axillary buds are lateral buds that arise in the axil of the leaf, e.g. Sunflower, Citrus, Rose. Accessory buds are more than one bud that arises in the axil of a single leaf. e.g. Cucurbita, Luffa, Brinjal, Chilly, Bougainvillaea. Subpetiolar buds are axillary buds those are covered by sheathing leaf base and appears to arise from leaf base. As they remain dormant for a quite long time they are also referred as dormant buds. When they gro they are referred as sprouting buds. e.g. Dalbergia sisso (Shisam) and Mulberry.

  • Bud Scales: In some plants, buds are covered by overlapping scales, these scales are called bud scales. These bud scales are tough and may be modified leaves, leaf bases, petioles or stipules. e.g. Jackfruit, Ficus and Magnolia.

  • Winter buds: In extremely cold regions plants bear specially protected buds called winter buds. During cold period leaves fall but the winter buds remain intact. During spring the bud opens with developing young leaves. e.g. Cauliflower, Cabbage.

  • Adventitious Buds: They arise at a position other than their normal position. Epiphyllous or foliar buds arise on leaves. e.g. Begonia, Bryophyllum, etc. Cauline buds arise from the cut or pruned end of branches. e.g. Sweet potato, Coffee, Aegle, etc. Radical buds develop on the roots. e.g. Sweet potato, Dahlia, Dalbergia.

  • Turions Buds:

 

Types of Stem: 

  • The stem may be
    • aerial (erect, rigid, strong and upright as in herbs, shrubs and trees)
    • subaerial (weak, unable to stay upright and trail on the ground as creepers or climb up as climbers) or
    • underground (buried in soil and produces aerial branches under favourable conditions only

Leave a Comment

Your email address will not be published. Required fields are marked *