Shoot System: Aerial Stem Modification and Functions of Stem: Primary and Secondary Functions (For CBSE, ICSE, IAS, NET, NRA 2022)

Doorsteptutor material for competitive exams is prepared by world's top subject experts: get questions, notes, tests, video lectures and more- for all subjects of your exam.

Aerial Stem Modification

Aerial modifications of stem perform unusual functions and are aerial in position. They greatly vary in form but can be distinguished easily by their position in the axil of a leaf or at the apex, bear nodes and internodes and may bear leaves, buds and flowers.

Table Showing Aerial Stem Modifications
Stem tendrilsThin, soft, long, wiry, leafless and spirally coiled structure, mostly found in climbers and helps the plant n climbingVitis vinifera (grape vine)
ThornsHard, straight, pointed and may be branched, thorns serve as defensive organsCitrus, Duranta, Carissa (karonda)
PhyllocladeGreen, flattened rounded stem with nodes and internodes, found in xerophytic plants, leaves modified into spines or scales to reduce transpiration, serve as photosynthetic and storage organsOpuntia (prickly pear) , Euphorbia
CladodePhylloclade with one or two internodes, resembles a leaf, arises in the axil of a much-reduced scale leaf and help in photosynthesisAsparagus
Image Showing Aerial Stem Modifications

Functions of Stem

Primary Functions

  • Mechanical Support and orient the leaves in a manner that they are exposed to maximum sunlight and for efficient gaseous exchange during photosynthesis and respiration. They also bear flowers and fruits.
  • Conduct water and minerals from to leaves and manufactured food from leaves to different parts of the plant. The stem conducts water and minerals from the root to the leaf.

Secondary Functions

  • Food storage – underground modified stems, it serves as a storehouse of food material, stems store food and water in plants e. g. , potato, ginger, onion etc.
  • Water storage – In many fleshy stems of cacti and euphorbias water is stored in sufficient quantity that is used by the plant in extreme dry conditions.
  • Photosynthesis – the young green stems and the modified stems of many cacti and other fleshy plants manufacture food material in the presence of sun light with the help of chloroplasts present in them.
  • Protection – Several modified stems into thorns protect the plants from grazing animals e. g. , citrus.
  • Perennation – Several modified underground food laden stems also serve as perennating organs, e. g. , potato, ginger, onion etc.
  • Vegetative propagation – Several aerial, sub-aerial and underground modifications of the stem help in vegetative propagation, e. g. , runner of doob grass, sucker of mint and sets of sugarcane.
  • Climbing – Tendrils or hooks are modified branches or buds. They coil around the support and help the plant to climb e. g. , grape vine.

Developed by: