Bark (botany)

Bark is the outer layer of woody plants.

It covers stems and roots. This layer protects the plant from bugs and sickness. It also keeps water inside the plant.

Some bark is very thick. People use bark to make many things. They use it to make canoes and ropes. Bark can even be used for food.

It is a very useful part of nature.

Bark is the outer layer of woody plants.

It covers the stems and roots of trees and shrubs. Bark has two main parts. The inner bark helps move food through the plant. The outer bark is often made of dead cells. This outer part is called the rhytidome.

Bark acts like a shield. It protects the plant from bugs and sickness. It also keeps water inside so the plant does not dry out. Some bark has a waxy substance called suberin. This helps stop water from escaping.

People use bark for many things. Some bark is used to make cork. Others are used for spices or medicines. In the past, people used bark to make canoes and ropes. Some people even use the inner bark for food.

Bark can also be damaged. Animals like deer might rub their antlers on it. Insects can also bite into it. Some plants can heal these wounds with new growth.

Bark is the protective outer layer of woody plants. This includes trees, shrubs, and woody vines. It covers the stems and roots to keep the plant safe.

Bark is made of different tissues. It sits outside a layer called the vascular cambium. The bark has an inner part and an outer part. The inner bark is living tissue that helps the plant. The outer bark is often made of dead cells.

Bark works like a shield for the plant. It protects against insects, diseases, and even fire. It also stops the plant from losing too much water.

Inside the cork cells, there is a waxy substance called suberin. This wax helps block water and germs. As a stem grows, the old outer skin dies. This creates a thick, rough layer called the rhytidome. This layer is most visible on the main trunk of a tree. New tiny holes called lenticels allow the plant to breathe gases.

Plants grow bark through a steady way it works. It starts with a layer called the epidermis. As the plant gets older, a new layer called the periderm forms. This forms from cells called the cork cambium. These cells divide to make new cork.

The cork cells eventually die and form a protective wall. This process replaces the old skin. Inside the bark, the phloem moves nutrients around. The vascular cambium is the only place where cells divide rapidly. It makes new wood on the inside and new phloem on the outside.

Bark is very useful to people and animals. Humans use bark for many different things. We use cork from the cork oak tree. We also use bark for spices, medicines, and even poisons.

Some people use bark to make cloth, ropes, or canoes. In Scandinavia, the Sami people use pine bark as a food. They can eat it fresh, dried, or roasted. Bark can also be used as building material for walls or roofs. Some plants are even grown just for their pretty bark colors.

Bark can sometimes get hurt by the world around it. Frost or hot sun can cause cracks. Animals like beetles or woodpeckers can also cause damage.

Even male deer can rub their antlers against bark. If the phloem is removed in a circle, the plant may die. This is called girdling. Some plants can heal by growing a callus over the wound. Other plants might use sap to seal the area. Many small living things, like moss or insects, live right on the bark.

Bark is the outermost layer found on the stems and roots of woody plants. This category includes trees, shrubs, and woody vines.

While herbaceous plants lack this covering, woody plants rely on bark for survival. Technically, bark refers to all the tissues located outside the vascular cambium. This layer overlays the wood and serves as a vital shield for the plant's internal systems. It is composed of various biopolymers, including lignin, tannins, and suberin.

The development of bark is a complex biological process. In young stems, the plant is covered by a thin layer called the epidermis. As the stem grows and thickens, this epidermis is replaced by a secondary covering called the periderm. The periderm forms from a layer of cells known as the cork cambium, or phellogen. This tissue acts as a lateral meristem, meaning it is a site of cell division. The cork cambium produces cork cells, also called phellem, which move toward the outside. It also produces a limited number of cell layers inside the cambium called phelloderm.

As these cork cells mature, they become impermeable to gases and water. The older cells on the outermost side of the periderm, such as the epidermis and cortex, eventually die. This creates the rough, protective surface we recognize as bark. Within the periderm, small openings called lenticels form. These lenticels contain numerous intercellular spaces. They are necessary because the living cells within the cambium layers must exchange gases to perform metabolism. As the bark continues to develop, new lenticels form within the cracks of the expanding cork layers.

Bark is organized into distinct functional layers. The inner bark consists of the phloem, which is a nutrient-conducting tissue. The phloem is made of sieve tubes or sieve cells mixed with parenchyma and fibers. This tissue transports photosynthetic products throughout the plant. The outer bark includes the dead tissues on the surface and the rhytidome. The rhytidome is the most familiar part of the bark, often forming the thick outer layer on tree trunks. It is produced by the formation of multiple layers of suberized periderm, cortical, and phloem tissue.

The chemical makeup of bark provides significant protection. Cork cell walls contain suberin, a waxy substance. This wax protects the stem against water loss, the invasion of insects, and infections from bacteria or fungal spores. Bark tissue typically makes up between 10% and 20% of the weight of woody vascular plants. Up to 40% of this tissue is composed of lignin. Lignin provides structural support by crosslinking with other polysaccharides like cellulose. Additionally, high concentrations of condensed tannin in the bark may inhibit decomposition.

Humans have utilized bark for thousands of years for diverse purposes. The cork from the cork oak tree is harvested for various products. Other barks provide spices, flavorings, medicines, and even resins or latex. In some cultures, the inner bark is a vital food source. For example, the Sami people of northern Europe use Pinus sylvestris bark as a staple food. In Scandinavia, bark bread is made by adding toasted, ground inner bark to rye. Bark has also been used as a construction material for roofing, wall cladding, and making canoes or ropes.

Despite its strength, bark can sustain significant damage. Environmental factors like frost cracks or sun scald can cause injury. Biological factors also play a role, such as attacks by boring beetles or woodpeckers. Even animals like male deer can damage bark by rubbing antlers against trees during the rutting season.

If the phloem is removed in a complete band around the stem, a process called girdling, the plant will usually die. This is because the transport of nutrients is interrupted. Some plants can repair damage by producing a callus growth, while others use sap to seal wounds.