To study of modification of stems.
The stem is the ascending part of the axis bearing branches, leaves, flowers and fruits. It develops from the plumule of the embryo of a germinating seed. The stem bears nodes and internodes. The region of the stem where leaves are born are called nodes while internodes are the portions between two nodes.
The main function of the stem is spreading out branches bearing leaves, flowers and fruits. It conducts water, minerals and photosynthates. Some stems serve as a source of food storage, support, protection, and vegetative propagation.
Examples: Passion fruit, Cucumber, Pumpkins, Watermelon etc.
Examples : Citrus, Bougainvillea.
Examples : Opuntia and Euphorbia
In these kinds of plants, the stem is present on the ground or partially underground. It grows horizontally under the soil and then comes above the ground and forms a new plant. They are used for faster propagation. These stems are modified into:
1. Runner – Runners are slender prostrate branches arising from axillary buds. It originates from the elongation of the basal internode and runs horizontally over the ground and gives rise to a new plant.
Examples: Grasses, Oxalis etc.
2. Stolon – A short and weak aerial branch arises from the main axis and after growing aerially for some time it bends downwards to touch the ground. A new plant develops from there.
Examples: Mint, Jasmine, Strawberry
3. Sucker – Sucker arises from the underground portion of the stem; it grows horizontally under the soil and then comes above the ground. It develops adventitious roots, shoots with leaves, and forms a new plant.
Examples: Chrysanthemum, Banana, Pineapple.
4. Offsets -They are found mostly in aquatic plants. Offset having a single long horizontal internode growing up to some distance producing a tuft of leaves above and a cluster of roots below at the apex
Examples: Pistia, Eichornia.