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in Stem - External Morphology by (46.2k points)
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Explain the different functions and general characteristics of the stem?

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Primary functions:

  1. It bears leaves and holds them in such a position so to provide maximum sunlight.
  2. The stem conducts water and mineral nutrients from the roots to the leaves, flowers and fruits.
  3. The stem conducts organic food from the leaves to the ’ roots and storage organs.
  4. It holds flowers in such a position so it facilitates 3. pollination and fertilization.
  5. The stem also bears fruits and seeds.

Secondary (or Accessory) functions:

  1. Storage: In many species, the stems act as the organs for storage of reserve food material (e.g., rhizome of Ginger, corm of Col ocas la. tubers of Potato, etc.), Sugars (e.g., Sugarcane) and water (e.g., Phylloclade of Opuntia).
  2. Synthesis of food: Some modified stems of xerophytic plants are green, flat and leaf like. They perform photosynthesis and help in the synthesis of food. Examples – Opuntia, Muehlenbeckia, Ruscus, Asparagus, etc.
  3. Perennation: Underground modified stems of many plants (e.g., Ginger, Curcuma) tide over the unfavourable conditions and help in perennation.
  4. Vegetative propagation: In many plants, stems sen e as means of vegetative propagation (e.g.. tubers of Potato, Suckers of Chrysanthemum, corms of Colocasia. etc.)
  5. Protection: Some stems bear thorns (e.g., Durcmtai, prickles (e.g., Rosa), etc. to protect the plants from browsing animals.
  6. Support: In weak-stemmed plants, the stem branches get modified into tendrils (e.g., Grape vine, Passiflora), thorns (e.g.. Bougainvillea) and hooks (e.g., Artabotrys) to help such plants to climb the support.

general characteristics of stem:

  1. Stem develops from the plumule and epicotyl of the embryo.
  2. Generally, it is an aerial and ascending part of the plant axis.
  3. A terminal bud is present at the apex of the main axis and lateral branches and is responsible for growth in length.
  4. A stem is differentiated into nodes and alternating intemodes. A node occurs where leaves are attached to the stem. Intemode is the portion of stem between the two nodes.
  5. Leaves emerge from the nodes .of the axis and its branches. The lateral organs of stem (i.e.. leaves and branches) are exogenous in origin.
  6. The young stem is green and performs photosynthesis.
  7. Multicellular hair may be present on the stem.
  8. Branches of the stem and its leaves have exogenous origin.
  9. Flowers and fruits develop on the stem of mature plants.
  10. It is generally erect and grows away from the soil towards light. Generally, a stem negatively geotropic and positively phototropic.

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