A bud is a compact and undeveloped young shoot in which the young rudimentary leaves with very short internodes are closely crowded.
The plumule in the embryo is the first bud and the shoot system develops from it. The development of the leaves in a bud is in acropetal succession. Based on their position, there are different types of bud.
Normally it occupies its position at the apex of the stem or branch which is said to be terminal or apical. When its position is in the axil of a leaf, it is known as axillaries. The elongation of stem depends on the growth of terminal bud. When the maxillary bud grows, it gives rise to branches.
The buds may be vegetative or floral. The former on development, form vegetative shoots and the latter, the flowers. If any extra buds develop by the side of the axillaries bud, these are known as accessary buds.
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Sometimes, adventitious buds are developed at various other parts of the plant such as the root (radical buds), e.g., sweet potato, or leaf (foliar buds), e.g., Bryophyllum or at different positions of the stem and the branches (cauline buds).
The functions of all these buds are to gradually develop into new branches, and in some plants into independent plants. Buds, which begin to grow and develop as soon as they emerge from the stem, are called active buds. In certain cases, they remain inactive for a period, and are called dormant buds.
A cabbage, cut longitudinally, gives a good idea about buds. Buds give rise to branches, leaves or flowers. Its protection in plants is provided by various means:
1. Overlapping of the young leaves on the delicate growing point of the bud protect the growing apex against sun and rain.
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2. Buds are protected by covering of hairs or in some cases by resinous or gummy secretions.
3. They are protected by bud scales in some cases also, e.g., banyan, jack- fruit and Magnolia, etc.
4. There may be a coating of wax or cutting on the leaf-surface to check evaporation of water and to prevent it from getting dry.