Question

characteristics of underground modification of stem​

Answer 1

Underground stem are modified plant structures that drive from stem tissue but exits under the soil surface.They function as storage tissues for food and neutrients ,propogation of new clones,and perennation (survival from one growing season to next)

Answer 2

Answer:

The Stem:

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

(i) Stem is an ascending axis of the plant and develops from the plumule and epicotyl of the embryo.

(ii) It is generally erect and grows away from the soil towards light. Therefore, it is negatively geotropic and positively phototropic.

(iii) The growing apex of stem bears a terminal bud for growth in length.

(iv) In flowering plants, stem is differentiated into nodes and internodes. A node occurs where leaves are attached to the stem. Internode is the portion of stem between the two nodes.

(v) The lateral organs of stem (i.e., leaves and branches) are exogenous in origin (from cortical region).

(vi) The young stem is green and photosynthetic.

(vii) Hair, if present, are generally multicellular.

(viii) In mature plants, stem and its branches bear flowers and fruits.

Functions of the Stem:

Primary functions of the stem are

• 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

Some stems perform the function of storage of food, support, protection and vegetative propagation. The secondary functions of the stem are

1. Storage: Some stems store food and water in some plants e.g. potato
2. Perennation: The underground stems help tide over the unfavourable growing periods e.g. ginger, turmeric.
3. Vegetative propagation: e.g. rose, and sugarcane the stem can be used for vegetative propagation.
4. Photosynthesis: In xerophytes (desert plants) the leaves are reduced to thorn, the stem possessing chlorophyll takes up the function of photosynthesis. e.g.Opuntia
5. Protection: In some plants, the axillary bud modifies into the thorn and protects the plants from grazing animals e.g. citrus, Duranta.
6. 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.

Types of Stem:

The stem may be

• aerial (erect, rigid, strong and upright as in herbs, shrubs, and trees) or
• 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

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