Bud

In botany, a bud is an undeveloped or embryonic shoot. These structures are vital for the continued growth and reproduction of plants. You can usually find them in the axil of a leaf or at the tip of a stem. An axil is the specific angle where a leaf meets the stem. Once a bud has formed, it may stay in a dormant condition for a while. This means it remains in a resting state without growing. Alternatively, a bud might develop into a new shoot immediately after it forms.

Many woody plants use specialized structures to protect their delicate embryonic parts. In temperate or cold climates, buds are often covered by scales. These scales are actually modified leaves that tightly enclose the bud. Some scales even feature a gummy substance to provide extra protection against the environment. As the bud develops and grows, the scales may enlarge slightly. However, they usually just drop off the plant. This process leaves behind horizontally-elongated scars on the surface of the growing stem.

These scars are very useful for scientists studying plant history. Because each year of growth ends with the formation of a bud, each year leaves a new group of bud scale scars. By counting these scars, one can determine the age of a young branch. As the branch continues to grow, these scars are eventually obliterated. This means you cannot use scars to determine the age of much older branches. Some plants, however, do not use scales at all. These are known as naked buds.

Botanists classify buds using several different criteria to describe them accurately. They look at location, status, morphology, and function. For location, a terminal bud is at the end of a stem. A lateral bud is found on the side. If a bud is in the leaf axil, it is called an axillary bud. Sometimes buds appear in unexpected places, like on a trunk or roots. These are called adventitious buds.

Status refers to how a bud behaves over time. An accessory bud is a secondary bud that forms alongside a principal bud. A resting bud forms at the end of a growth season and waits for the next one. If a bud waits for a very long time, it is called a dormant or latent bud. Some buds, known as epicormic buds, may stay undeveloped for years. In certain species like beech or persimmon, an axillary bud can take over the job of a terminal bud. This is called a pseudoterminal bud.

Morphology describes the physical shape and covering of the bud. A bud can be scaly, also known as perulate, which means it is covered by perule. These perule are transformed and reduced leaves. A bud can also be naked if it lacks scales. Some buds are hairy to provide protection. Finally, buds are classified by their function. A vegetative bud contains only vegetative structures like leaves. A reproductive bud contains only embryonic flowers. An inflorescence bud contains an entire inflorescence. Some buds are mixed, containing both leaves and flowers.

Buds can reach surprising sizes and forms in the plants we eat. For example, a head of cabbage is an exceptionally large terminal bud. Brussels sprouts are another example, as they are large lateral buds. In the wild, some plants show a beautiful gradation of scales. In a buckeye tree, you might see a transition from small brown outer scales to larger green inner scales. These inner scales are remarkably leaf-like. This suggests that bud scales are indeed modified leaves designed to protect the plant during unfavorable periods.