Sunday, December 20, 2009

study of stem modifications-pharma-D-lab manual


.aerial stem modification

To study about various types of stem modifications in plants

Modification is a change as a result of its environment that helps that particular organism to acclimatize to that specific environmental conditions. such modifications which occur in the stems of the plants are called stem modifications.
There are many stem variations in plants. Some variations are forms of food, such as potatoes and asparagus. Others are forms sold in dormant condition for introduction into the landscape as new plants, such as dahlia tubers and tulip bulbs. The runners of strawberries are an example of a stem modification (stolon) used for PROPAGATION. Rhizomes (RYE-zohms), the horizontal underground stems of plants, such as bentgrass, allow the spreading of plant.
Types of stem modifications
.aerial stem modification
.subaerial stem modifications

Stem Tendril
Tendrils develop as modifications of the stem in certain plants. The terminal bud gives rise to a tendril in Cissus quandrangularis and the axillary bud becomes modified into a tendirl in Passiflora.

Stem Thorn
2. Thorns. These are hard, pointed, straight structures. These are modified axillary or terminal buds. They act as organs of defence. In Duranta and Prunus the thorn bear leaves. In carissa thorns are modified terminal buds.

Phylloclade. These are green flattened stems having nodes and internodes with leaves reduced to spines. In Opuntia and Euphorbia the phylloclade are succulent and conserve water. It is a characteristic of xerophytes.

Cladodes and Cladophylls
A phylloclade of one or two internode is called as a cladode.

Bulbil is a speical multicellular body essentially meant for reproduction. In Agave the floral buds are modified into bulbils. These bulbils get detached, come in contact with the soil and develop into new plants. In Dioscorea the axillary bud develops into a bulbil. This bulbil detaches from the mother plant and grows up into a new independent one.


The runner arises from the base of the stem as a lateral branch and runs along the surface of the soil. It develops distinct nodes and internodes.E.g., Oxalis, Fragaria, Centella astatica.

An offset is a short thick runner like branch which produces a new plant at its tip. The offsets grow in all directions from the main stem of the parent plant.

Here, lateral branches called stolons originate from the underground stem. The stolons grow horizontally outwards for a varying distance in the soil. Ultimately their end (terminal bud) emerges out of the ground and develops into a new plant. A runner, sucker or any basal branch which produces roots is called a stolon. E.g. Colocasia.

A lateral branch arising close to the ground level, traveling underground for some distance, turning up at its end and producing a new plant is a sucker. Eg. Chrysanthemum


STEM MODIFICATIONS OfChrysanthemum,Colocasia,Dioscorea,Opuntia,boganvillia,Cissus quandrangularis were observed

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