The Ins and Outs of the Plant Stem

The Ins and Outs of the Plant Stem

A plant stem not only supports the leaves and flowers, but it is vital in the movement of nutrients between the roots to the leaves. In this post, we discuss the ins and outs of the plant stem.

Stems fall into two categories: soft or woody. Soft stems are bendable and flexible. A fancy word for soft stems is herbaceous stems. These stems stay green and are usually shorter than plants with woody stems. Woody stems are covered in bark and are strong with some flexibility.

In woody plants, the age of the stem determines its name. A twig is young, less than one year old, and a branch is more than one year old. The trunk is the oldest and main stem.

External Structure of a Plant Stem

The external structures of a stem tell you a great deal about the plant’s history and health.

Buds

A bud is a point on the stem where growth occurs. This growth is either a leaf or a flower. Flower buds tend to be more round than leaf buds.

There are two categories of buds: terminal and lateral. Terminal buds are at the tip of the stem. Lateral buds are on the side of the stem.

When a terminal bud is present, many plants send most of their energy to this point, reducing the energy given to the lateral buds. Cutting the terminal bud allows the plant to push energy to the lateral buds, creating a bushier plant.

Scars

Just like us, plants get scars. These scars are from leaves or terminal buds. The leaf scar indicates where a leaf was attached to the stem. The bundle scars show where the veins or vascular tissue flowed through the base of the leaf into the stem.

Terminal bud scale scars are left when the terminal bud falls off. These scars help measure the annual growth of a plant. It is also a good determination of the plant’s hardiness.

Lenticel

Lenticels are pores or holes on the stem. These holes stay open, allowing the exchange of gases between the stem and the air.

Node and Internode

A stem is broken up into two parts. The node is where the leaves and lateral buds attach to the stem. The internode is the area of the stem in between the nodes.

Bark

Bark covers woody-stemmed plants. It thickens as the plant ages. This outer protective tissue has different patterns and textures, depending on the plant species. It also helps in plant identification.

Internal Structure of a Plant Stem

Before getting down deep into the stem, let’s take a look at its outer layers.

Apical Meristem

The apical meristem tissues reside in the terminal bud at the tip of the stem. Cells in these tissues divide, causing the stem to grow in length.

Epidermis

The epidermis is the outer layer of the stem. It provides protection. The bark of a tree is its epidermis.

Cortex

The cortex is the tissue between the epidermis and the vein, or vascular tissue of the stem. It helps store starches or food for the plant.

Now we dive deep. The inner layers of the stem consist of the vascular tissue. This vascular tissue moves food and water up to the leaves and down to the roots. The fancy word for this movement is translocation.

Phloem

Phloem is sometimes called the inner bark. These tissues carry the sugars or food from the leaves to the rest of the plant.

Cambium

Cambium tissues supply the plant with phloem and xylem tissues through tissue division. It creates phloem towards its outside and xylem towards its inside. By creating tissue in this manner, the cambium adds width to the stem. Cambium creates the rings of a tree.

Xylem

Xylem is the tissue that transports water and minerals from the roots to the rest of the plant. The xylem is what gives the plant support.

Pith

Pith is at the center of some stems. It is here that the plant stores sugars.

Types of Modified Stems

Not all stems grow upright and above ground. Some stem structures develop new functions according to their environment. There are three different groups of modified stems. How do we know some of these are stems? They have three important distinctions:

1. They have nodes and internodes.
2. The inside looks like a stem and not a root.
3. They have small (scale) leaves, buds, and roots that form on a stem.

Underground Stem Modification

Rhizome

Rhizomes grow horizontally underground, right around ground level. When you think of plants with rhizome stems, plants that spread quickly come to mind, such as mint, iris, ginger, and canna lilies.

Corm

A corm grows underground and is short and thick. These stems may look like bulbs, but they are solid inside. The flowers and leaves use the nutrients stored in the corm as they grow. The corm eventually disappears. Examples of corms include gladiolus, crocus, and freesia.

Bulb

Bulbs are thick, underground stems. They are little storage units that contain layers of modified leaves and a bud or sprout in the center. Bulbs have roots at the bottom to anchor them into the ground. Examples of bulbs are lilies, onions, daffodils, and tulips.

Tuber

A tuber is an underground modified stem. The plant uses this part of the stem as food storage. Potatoes are an excellent example of tubers.

Subaerial Stem Modifications

Subaerial stems grow partly above ground and partly below ground.

Stolons

Stolons develop in an arch from the original plant. They then dive down towards the ground, creating roots and new plants from their tips. A great example of stolons is strawberry plants.

Runners

Runners are modified stems that creep away from the original plant, horizontally close to the ground. They produce roots along each node, creating new plants. The main difference between runners and stolons is the method of moving across the ground. Runners are close to the ground while stolons move in an arch.

Sucker

A sucker grows underground and then pops up to form another plant after the roots take hold. Examples of plants with sucker stems are banana trees, mint, and chrysanthemums.

Offset

Offset modified stems occur in aquatic plants. These stems are very much like runners. However, they are shorter and thicker. Some plants with offset stems are water hyacinth and pistia.

Aerial Stems

Aerial stem modifications are changes in the original above-ground stem.

Tendrils

These spirally twisting modified stems develop from buds. They help with plant support by grabbing onto a support and wrapping themselves around it. Examples of plants with modified tendril stems include passionflower and the common grape.

Stem Thorns

Stem thorns are woody, pointy structures formed at the bud. They protect the plant. Plants that have thorns are bougainvillea, pomegranate, and citrus.

Hooks

Hooks are like thorns but curved instead of straight. Unlike thorns, hooks are not a means of protection. Instead, they help the plant climb.

Phylloclade

Phylloclade modifications are in plants that live in habitats with very little water. They are flat or swollen and green and take on the job of photosynthesis. These modified stems look like leaves, but they are not.

Spurs

A twig that bears leaves, flowers, and fruits. It is usually stubby. These spurs generally occur on fruiting trees, such as pears, apples, and ginkgo.

Bulbils

Bulbils form at the angle between the leaf and the stem. They act as additional storage for food. As they grow, they mature into new plants.

Tuberous Stems

Tuberous stems are short and flat. These stems serve as additional food storage for the plant. Bud grow from the top, and roots grow from the bottom.

Twining Stem

Twining stems help plants climb upwards by wrapping themselves around objects. Black-eyed Susan’s and pole beans are examples of plants with this stem modification.

Phew! We covered a lot in this article. Who knew there was so much to discover with stems? Something so simple is quite complicated. If you can believe it, there is more intricate information about stems that we didn’t even touch.

Other Related Articles

• Parts of a Plant
• Structure of a Leaf
• Pruning

The Ins and Outs of the Plant Stem