Pith

Plants have a soft part in their stems.

This part is called pith. It is soft and spongy. It can hold food for the plant.

New pith is often white. It can turn brown as it gets old. Some plants have hollow stems. This happens when the pith dries out.

Some plants even have many small holes. Pith is also the white part inside an orange. It is a very useful thing to find!

Pith is a soft part found in plant stems.

It is made of spongy cells called parenchyma. These cells can store starch, which is a type of food. In some plants, the pith sits in the center of the stem. In other plants, it only grows in the roots.

New pith is often white or pale. As it gets old, it turns brown. In big trees, the pith might go away. It is often replaced by xylem, which is wood. Some plants have hollow stems because the pith dries out. Walnut trees have a special kind of pith. It has many small holes or chambers.

People use pith in many ways. The pith of the sago palm is a food source. It has a lot of starch. People must clean it to remove toxins. This makes it safe to eat. Pith wood is also used by watchmakers. They use it to clean oil off small tools.

Long ago, people used dried pith for light. They soaked it in fat to make a rushlight.

Pith is a soft part found inside many plant stems. Scientists also call this tissue the medulla. It is made of spongy cells called parenchyma. These cells can hold onto starch, which is a type of stored energy. In some plants, like eudicotyledons, the pith sits right in the center. In monocotyledons, it only grows into the roots. The pith is surrounded by a ring of xylem. This xylem is then surrounded by a ring of phloem.

Plants change as they grow older. New pith is usually white or a very pale color. As the tissue ages, it often turns a deep brown. In large trees, the pith is mostly in young growth. In old trunks or branches, xylem often takes its place. Some plants have stems that become hollow. This happens when the pith dries out and breaks apart. Walnut trees are different because they have chambered pith. This means they have many small holes inside.

Humans have used pith for many different jobs. People in Melanesia and Micronesia use sago palm pith for food. The pith has a lot of starch in it. However, the raw pith is toxic to animals. People use a process to leach the toxins away. This leaves only the starch to be eaten. The finished starch looks a lot like tapioca. This process is about 50% efficient today.

Other tools and lights have used pith too. Watchmakers use pith wood to clean their small tools. They use it to wipe oil off the tips. This keeps the watch movements very clean. In the past, people used rush plants for light. They soaked the dried pith in fat or grease. This was called a rushlight. People used these from the 17th century until the mid-20th century. They even saw a short use during World War 2.

Sometimes we use the word pith for other things. It can mean the pale inner layer of a citrus fruit. This part is also called the mesocarp or albedo. This is the spongy part of an orange. The word itself comes from an Old English word. That word, piða, means substance. It is related to the Dutch word pitte. This means the pit of a fruit.

Pith, also known as the medulla, is a specialized tissue found within the stems of vascular plants. It is primarily composed of soft, spongy parenchyma cells. These cells serve several biological roles, such as storing starch for the plant. The location and structure of pith vary depending on the type of plant. In eudicotyledons, the pith is situated at the very center of the stem. In monocotyledons, however, the pith extends only into the roots. The tissue is organized in a specific sequence within the plant's anatomy. The pith is encircled by a ring of xylem, which is the tissue that moves water. This xylem is then surrounded by an outer ring of phloem, which transports nutrients.

As plant tissue matures, its physical properties often undergo noticeable changes. New pith growth is typically white or a very pale color. As the tissue ages, it commonly darkens to a deeper brown shade. In many trees, pith is a prominent feature of young growth. However, as a tree develops an older trunk or larger branches, the pith is often replaced by xylem. This replacement process means the center of an old tree is quite different from a sapling. In some plant species, the pith in the middle of the stem may dry out. When this happens, the tissue disintegrates and leaves the stem hollow.

Some plants exhibit much more complex pith structures than others. For example, walnut trees possess what is known as chambered pith. This structure contains numerous short cavities within the tissue. In certain plants, the cells on the outer edges of the pith develop differently than the inner cells. This specific layer is called the perimedullary region of the pithamus. One species that shows this distinct cell development is Hedera helix, commonly known as ivy. These variations in cell structure show how specialized plant tissues can become.

Humans have found several ways to utilize pith for survival and industry. In Melanesia and Micronesia, the pith of the sago palm is a vital food source. This is due to the high starch content found within the tissue. However, the raw pith is highly toxic to animals and humans. To make it safe, people use a process to leach the toxins away from the starch. This extraction process allows only the safe starch component to be consumed. The resulting starch is very similar in appearance to tapioca. Currently, these extraction processes are generally about 50% efficient. This means half of the material remains as residual pith waste.

Beyond food, pith has served important roles in historical technology and maintenance. In the field of watchmaking, pith wood is used as a specialized cleaning tool. Watchmakers use pieces of pith, such as from the elder or mullein plants, to clean their equipment. The spongy nature of the wood allows it to remove oil from the tips of small tools. This prevents oil from contaminating the delicate movements inside a watch. Additionally, the spongy wood of the pith wood plant was once used to manufacture pith helmets. Although often mistakenly called pith, this material provided a lightweight and protective structure.

Historical lighting methods also relied on the unique properties of pith. From the 17th century until the mid-20th century, people used rushlights for home lighting. This method involved using the dried pith from certain rush plants. This pith is actually the center of the leaf. To create a flame, the dried pith was soaked in fat or grease. This setup allowed for a steady, albeit small, source of light. This method even saw a brief period of revival during World War 2.

The term "pith" is also applied to different biological structures in other contexts. In botany, it can refer to the pale, spongy inner layer of the rind in citrus fruits. This layer is more accurately called the mesocarp or the albedo. You can see this in fruits like oranges, which belong to the hesperidia group. The linguistic history of the word provides a clue to its meaning. It originates from the Old English word "piþa," which means substance. This is closely related to the Middle Dutch word "pitte," which refers to the pit of a fruit.