Shoot System: Stem and Its Characteristics, the Shoot Apex, Origin of Lateral Branches and Types of Stem (For CBSE, ICSE, IAS, NET, NRA 2022)

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Characteristics of Stem

  • The stem is the ascending portion of the axis of the plant
  • Develops directly from the plumule, the stem is provided with nodes and internodes which may not be distinct in all cases
  • When the stem or the branch ends in a vegetative bud it continues to grow upwards or sideways, bears leaves, branches and flowers on nodes
  • They are negatively geotropic and positively phototropic, and the stem bears different kinds of buds, e. g. , axillary, terminal and floral buds.

Differences between Stem and Root

Table Showing Differences between Stem and Root
The stem is the ascending portion of the axis and it turns towards lightThe root is the descending portion of the axis of the plant and grows away from light
Develop from plumuleDevelop from radicle
Young stem is green colored because of chlorophyllNon-green because chlorophyll absent
Divided into nodes and internodesNot divided into nodes and internodes
Bears leaves, vegetative and floral budsAbsent
No cap present at the apexRoot cap is present at the apex
Positively phototropic and negatively geotropicNegatively phototropic but positively geotropic
Origin of lateral branches is exogenous (originating from outer layers)Origin of lateral roots is endogenous (originating from inner layers)
The shoot hairs prevent evaporation of water from the surface of the stemRoot hairs absorb water and minerals from the soil
Branches are exogenous i.e.. they arise from the outer layersBranches are endogenous i.e.. they arise from the pericycle

The Shoot Apex

  • Shoot apex is the terminal, dome-shaped part of the shoot and is formed of meristem called apical meristem is responsible for the development and differentiation of primary permanent tissue and mainly causes growth in lengths.
  • According tunica-corpus theory proposed by Schmidt (1924) consists of an outer layer of tunica: 1 - 3 layer thickness, forms protoderm for epidermal tissues and is responsible for surface growth and inner mass of corpus: is multi-layered zone of cells which in all directions, forms procambium for vascular tissues and ground meristem for ground tissues. These cells also form leaf primordia for a newly developing leaf.
Image Showing L. S. Of Vegetative Shoot Apex

Origin of Lateral Branches

Branches arise from axillary buds present in the axil of leaves. Each axillary bud is 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) .

Types of Stem

There are three types of stem: Underground stem, Aerial stem and Sub- aerial stem.

  • Underground stem: buried in soil and produce aerial branches under favorable conditions only and storage of food.
  • Aerial stem: erect, rigid, strong and upright as in herbs, shrubs and trees.
  • Sub-aerial stem: weak, short, lateral branches, unable to stay upright and trail on ground as creepers or climb up as climbers.

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