Modifications of Stems - ep1

Stem modifications are structural changes that occur in plant stems, categorized into aerial modifications that develop above the ground, subaerial modifications that grow both above and below the ground, and underground modifications that exist below the ground.

Aerial modifications in desert plants

In typical plants, broad leaves expose a large surface area to sunlight and lose significant amounts of water. Desert plants face extreme heat and scarce water, leading to aerial stem modifications known as phylloclades. In a phylloclade, the stem itself becomes thick and swollen to store whatever water is absorbed. To further prevent water loss under intense sunlight, the leaves shrink and transform into sharp spines or thorns instead of expanding into wide blades.

Runners and offsets

• Runners are subaerial stems that spread horizontally across the ground, featuring multiple nodes and internodes.
• When a runner node touches the soil, it sprouts roots downward and shoots upward, allowing grasses to continuously spread across fields.
• Offsets operate similarly to runners but occur on the surface of water rather than on land.
• Water hyacinth stems are thick and swollen because they contain aerenchyma tissue, which stores air to help the plant float.
• An offset differs from a runner by having only a single internode between the parent stem and the new plant node.

Suckers and stolons

• Suckers begin from an underground stem or rhizome and travel beneath the soil for a long period before turning upward toward the surface.
• As the sucker reaches the surface, roots form at its nodes and a new shoot sprouts, with the connecting stem hidden underground, as seen in banana plants.
• Stolons also start from an underground stem, but their branches immediately grow upward to run along the ground surface.
• Stolons contain numerous nodes and internodes that take root upon touching the soil, enabling plants like mint, strawberry, and chrysanthemum to propagate.