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Aerial stem modifications are modifications to the aerial stems, vegetative
buds In botany, a bud is an undeveloped or embryonic shoot and normally occurs in the axil of a leaf or at the tip of a stem. Once formed, a bud may remain for some time in a dormant condition, or it may form a shoot immediately. Buds may be speci ...
and floral buds of plants growing in different conditions and which perform functions such as climbing, protection, support, synthesis of food, or vegetative propagation. Aerial stem structures that undergo modifications to perform these special functions include
tendrils In botany, a tendril is a specialized stem, leaf or petiole with a threadlike shape used by climbing plants for support and attachment, as well as cellular invasion by parasitic plants such as ''Cuscuta''. There are many plants that have tend ...
, thorns, hooks,
phylloclade Phylloclades and cladodes are flattened, photosynthetic shoots, which are usually considered to be modified branches. The two terms are used either differently or interchangeably by different authors. '' Phyllocladus'', a genus of conifer, is nam ...
, tuberous stems and
bulbil A bulbil (also referred to as bulbel, bulblet, and/or pup) is a small, young plant that is reproduced vegetatively from axillary buds on the parent plant's stem or in place of a flower on an inflorescence. These young plants are clones of the par ...
s. The auxiliary or the terminal part of the modified structures show their stem nature.


Tendrils

Some weak stemmed plants produce wiry, coiled, sensitive and delicate organs for climbing. They are called tendrils. These may develop from either the axillary bud or the terminal bud of the stem. In ''
Passiflora ''Passiflora'', known also as the passion flowers or passion vines, is a genus of about 550 species of flowering plants, the type genus of the family Passifloraceae. They are mostly tendril-bearing vines, with some being shrubs or trees. They ...
'', the tendrils develop from the axillary bud. In ''
Cissus quadrangularis Cissus quadrangularis is a perennial plant of the grape family. It is commonly known as veldt grape, winged treebine or adamant creeper. The species is native to tropical Asia, the Arabian Peninsula and much of Africa. Description ''Cissus ...
'' and in '' Vitis vinifera'' the terminal bud develops into tendrils.


Thorns

These are hard, woody, pointed structures meant for protection. They are provided with
vascular tissue Vascular tissue is a complex conducting tissue, formed of more than one cell type, found in vascular plants. The primary components of vascular tissue are the xylem and phloem. These two tissues transport fluid and nutrients internally. There ...
, which may develop from the axillary bud or terminal buds. They control transpiration by reducing the vegetative growth. In ''
Bougainvillea ''Bougainvillea'' ( , ) is a genus of thorny ornamental vines, bushes, and trees belonging to the four o' clock family, Nyctaginaceae. It is native to eastern South America, found from Brazil, west to Peru, and south to southern Argentin ...
,
Punica granatum The pomegranate (''Punica granatum'') is a fruit-bearing deciduous shrub in the family Lythraceae, subfamily Punicoideae, that grows between tall. The pomegranate was originally described throughout the Mediterranean region. It was introduc ...
and
Duranta ''Duranta'' is a genus of flowering plants in the verbena family, Verbenaceae. It contains 17 species of shrubs and small trees that are native from southern Florida to Mexico and South America. They are commonly cultivated as hedges and ornamen ...
'' the axillary bud develop into thorns. In ''Duranta'', the thorns are provided with leaves and flowers. In ''Punica granatum'', the thorns bear leaves and branches. In ''
Carissa carandas ''Carissa carandas'' is a species of flowering shrub in the family Apocynaceae. It produces berry-sized fruits that are commonly used as a condiment in Indian pickles and spices. It is a hardy, drought-tolerant plant that thrives well in a wide r ...
'' the terminal bud produces a pair of thorns. They help in protection.


Bulbils

When axillary bud becomes fleshy and rounded due to storage of food, it is called bulbil. It gets detached from the plant, falls on ground and develops into a new plant. e.g. '' Dioscorea''. It is in axel (the space between leaf and stem)


Cladode

These are green branches of limited growth (usually one internode long) which have taken up the functions of photosynthesis. True leaves are reduced to scales or spines, e.g. '' Asparagus''.


References

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