Vegetative propagation and climbing are two examples of aerial stem modifications. Climbing, protection, and support are all examples of aerial stem modifications. Photosynthesis, food synthesis, and vegetative reproduction are all examples of aerial stem modifications. Tendrils, thorns, hooks, phylloclade, tuberous stems, and bulbils are examples of aerial stem structures that have undergone modifications in order to perform these specialised functions. The auxiliary or terminal part of the modified structures demonstrates the stem nature of the modified structures. In addition to providing structure and support, the stem also aids in the growth of the plant. 

Three important types of modifications are made to it:

• Modification of the Stem
• Sub-aerial Modification 
• Modification of the Stem by Aerial Agents

Underground Modifications of the Stem

The structure of some underground stems has been altered to accommodate food storage and the ability to survive in adverse conditions. 

The following are examples of underground stem modifications:

Rhizome

These are non-green and have distinct nodes and internodes, as opposed to the others. There are auxiliary buds in addition to apical buds. These have a brownish hue to them. Rhizomes of the most common types are fleshy, which is due to the fact that they store food material. It also has terminal buds on the ends of the stem. For example, ginger. Instead of growing horizontally, the rhizome rootstock grows vertically upwards. The rhizome is found in a variety of plants, including bananas and Alocasia indica.

Bulb

There are numerous fleshy scale leaves to be found. The adventitious roots that form the bulb’s base form a cluster at the bulb’s base. For example, onions and garlic. The bulb can be tunicated or scaley in appearance. The tunicated bulb is protected by a sheath of dried membranous scale leaves. A scaley bulb is devoid of any tunic.

Corm

The vertical growth direction of this condensed form of the stem is indicated by the arrow. In appearance, it has a spherical shape with a flattened base. There are distinct nodes and internodes in this graph. Adventitious roots can be found at the base of the plant or throughout the plant’s entire body. The auxiliary buds are located on the sides of the plant. For example, Colocasia.

Tuber

It is a fleshy part of the plant that serves as a food storage area. Potatoes are the most common tuber and are primarily used as food in the United States. The lower part of the potato is covered by the earth, which is where the adventitious branches begin to grow. Every node is represented by an eye, which are depressions in the surface of the graph. There are no adventitious roots in this plant. These are primarily used as food, and they grow at a snail’s pace.

Modifications of the Stem that occur in the subaerial space

In these types of plants, the stem is partially above ground and partially below ground, depending on the species. These are rewritten as follows:

Runner

Creepers are plants that spread horizontally across the surface of the soil. Scale leaves, adventitious roots, and auxiliary buds can be found at the nodes. Runners appear as a result of the auxiliary buds. By breeding in all directions, a mother runner can produce a large number of runner offspring. Runners break off and develop into a self-sufficient plant, which results in vegetative propagation of the plant. For example, C-Cynodon. Sobole is the term used to describe an underground runner.

Sucker

It grows from the base of the main stem, which is where it gets its name. It develops adventitious roots and leafy shoots prior to separating from the mother plant before separating. It begins by moving horizontally beneath the soil for a short distance before growing obliquely upwards. For example, Mentha

Stolon

These begin to grow in the air for a period of time before bending downwards to touch the ground. The terminal bud in this case gives rise to a new stem as well as adventitious roots. Stolon is a branch that grows from the base of the main stem. For example, Jasmine. In horticulture, branches are lowered to the ground until they meet the soil and strike the root system. Mentha spicata is a plant that has naturally occurring stolons.

Offset

It is found in aquatic plants and is shorter and thicker in comparison to terrestrial plants. It develops from the leaf’s axis and spreads horizontally as it develops. For example, Pistia. The leaves are produced above ground, and the adventitious roots are produced below ground. It is a short runner with only one internode in terms of overall length.

Aerial Modifications of Stem

• Airborne Alterations to the Plant’s Stem: Several important functions are performed by the stems when they are transformed into aerial forms, such as climbing, food storage, vegetative propagation, and protection.

The modifications to the stem are as follows:

• Tendrils on the stem: Tendrils are threadlike leafless structures that develop on the stem as a result of this modification. These are intended for use as climbing shoes. There may or may not be a branch in each of these. The following are examples of stem tendrils:

1. Passiflora is an example of an axillary plant.
2. Extra-axillary plants include, for example, Luffa.
3. Grapevine, for example, has an apical bud.
4. Antigonon is an example of a floral bud.

• Thorns: Typically, these are pointed, hard structures that may or may not have leaves, branches, and flowers growing on them. Thorns are formed from the terminal bud of the plant. Thorns are used as defence organs, and they also aid in the regulation of transpiration. For example, Bougainvillea.

Thorns can be distinguished from spines and prickles because they are deeply rooted and have vascular connections to the surrounding tissue. Prickles are plant growths that are only visible on the surface of the plant. Spines are plant organs that have been modified.

• Phylloclades: These are leaves that have been modified into scales or spines in order to reduce transpiration. This is accomplished through the control of the growth of the leaves. Their fleshy, green skins contribute to photosynthesis, as does their presence in the ocean. This modification can be found in xerophytic plants, which are able to store water. For example, Opuntia. In this plant, the leaves are modified into spines or small scaly leaves, and the internodes are made of fleshy tissue.

• Cladodes: It is a phylloclade that has only one internode, as the name suggests. These are cylindrical in shape, but they are not fleshy. These contribute to the process of photosynthesis. Asparagus is an example. In this case, the leaves have been modified to have prickles.

• Bulbils: These are modified axillary vegetative or floral buds that are intended to be used for food preservation. They go through the process of vegetative propagation in order to produce a new plant. For example, Dioscorea. Bulbulils are auxiliary buds that have been condensed in this case.

• Thalamus: It is the axis of the flower and contains the flower organs such as the calyx, the corolla, the androecium, and the gynoecium, among other components. Silene’s nodes and internodes are clearly defined.

Conclusion

The stems of some plant species have been modified to make them more suitable for a specific habitat and environment than others. It has nodes and internodes, and it grows horizontally underground. A rhizome is a modified stem that grows horizontally underground. Some plants, such as ginger and ferns, have the ability to produce vertical shoots from the buds on their rhizomes. Corms are similar in appearance to rhizomes, with the exception that they are more rounded and fleshy (such as in gladiolus). Corms are a type of food storage that allows some plants to survive the winter months. Stolons are stems that run almost parallel to the ground or just below the surface of the ground, and the nodes of these stems are capable of producing new plants.