Subaerial stem

The stem is the section of the axis that ascends and bears branches, leaves, flowers, and fruits. It grows from the plumule of a sprouting seed’s embryo. There are nodes and internodes in it. Nodes are the parts of the stem where leaves are born. Internodes, on the other hand, are the areas between two nodes. 

Types of stem

Stems in many plants provide a variety of purposes, including perennation, vegetative propagation, food storage or synthesis, and so on. The stem is separated into three categories, each of which is further subdivided into groups based on their variations. There are three sorts of stems: 

1. Underground stem 

2. Aerial stem 

3. Subaerial stem 

Underground stem

Underground stems are plants that have been engineered to generate from stem tissue yet dwell beneath the soil surface. They serve as food and nutrition storage tissues, as well as new clone propagation and perennation (survival from one growing season to the next). Bulbs, corms, rhizomes, stolons, and tubers are among the several types. 

Aerial modifications of stem

Climbing, food storage, vegetative proliferation, and protection are all crucial functions for stems that have been transformed into aerial forms. The following are the stem modifications: 

Stem Tendrils

Tendrils are threadlike leafless structures that develop from the stem. These are designed to be used for climbing. There isn’t always a branch in these. Here are some examples of stem tendrils: 

Axillary: E.g., Passiflora

Extra-axillary: E.g., Luffa

Apical bud: E.g., Grapevine

Floral Bud: E.g., Antigonon 

Thorns

These are hard, pointed structures that may or may not have leaves, branches, or flowers on them. The thorns form from the terminal bud. Thorns serve as defence organs and aid in the control of transpiration. Bouganvillea, for example.

Thorns differ from spines and prickles in that they are deeply embedded and have vascular connections. Prickles are the plant’s outermost growths. Plant organs that have been changed are called spines. 

Phylloclades

To control transpiration, these leaves have been transformed into scales or spines. This is accomplished by limiting the growth of the leaves. These are green, squishy, and participate in photosynthesis. Xerophytic plants have this modification, which reserves water. Opuntia, for example. The leaves are changed into spines or little scaly leaves, and the internodes are mushy. 

Cladodes

There is only one internode in this form of phylloclade. These are cylinders that aren’t meaty. Photosynthesis is aided by these. Asparagus, for example. The leaves are turned into prickles in this method. 

Bulbils

These are food-storing modified axillary vegetative or floral buds. To create a new plant, they go through vegetative propagation. Dioscorea, for example. The bulbils are auxiliary buds that have been compressed. 

Thalamus

The flower’s axis contains the calyx, corolla, androecium, and gynoecium, among other flower organs. Silene has well-defined nodes and internodes. 

Subaerial modifications of stem

These plants’ stems are partially above ground and partially underground. These are changed to: 

Runner

It’s a creeper that grows horizontally on the soil’s surface. At the nodes, scale leaves, adventitious roots, and auxiliary buds can be detected. Auxiliary buds give rise to runners.

A mother runner produces a vast number of runners in all directions. Runners split off and grow into their plants, allowing for vegetative replication. C-Cynodon, for example.

Sobole is a type of underground runner. 

Sucker

It is derived from the main stem’s base. It generates adventitious roots and leafy shoots before separating from the original plant. It develops obliquely upwards after moving horizontally under the soil for a while. Mentha, for example. 

Stolon

These grow in the air for a while before bending down to touch the ground. A new stem and adventitious roots emerge from the terminal bud. Stolon grows from the main stem’s base. Jasmine, for example.

Branch tips are lowered to reach the earth where they strike the root in horticulture. Mentha spicata has natural stolons like this. 

Offset

It is present in aquatic plants and is shorter and thicker. It sprouts from the leaf’s axis and spreads horizontally. Pistia, for example. The leaves are generated above ground, and the adventitious roots are produced below ground. It’s a short runner with only one internode. 

Conclusion

A stem is used for a variety of functions, including photosynthesis, which is necessary for many metabolic processes. It gives a plant that will eventually grow into a tree a precise structure and base. The fundamental role of the stem is to support the plant’s buds, flowers, leaves, and fruits. The roots are connected to the plants by a stem, which allows them to stand upright and perpendicular to the ground. It distributes water and minerals from the root to many different parts of the tree, as well as prepares food from the leaves.