Aerial stem modification
Ariel stem modifications are modifications to the aerial stems, vegetative buds and floral buds of plants which perform functions such as climbing, protection, synthesis of food vegetative propagation,etc.the auxiliary or the terminal part show their stem nature.
The aerial stems, vegetative buds and floral buds of plants growing in different conditions undergo modifications to perform special functions. These modifications are called "aerial stem modifications'. They include tendrils, thorns, hooks, phylloclade, tuberous stems and bulbils.
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, the tendrils develop from the axillary bud. In Cissus quadrangularis. And in Vitis vinifera the terminal bud develops into tendrils.
These are hard, woody, pointed structures meant for protection. They are provided with vascular tissue, which may develop from the axillary bud or terminal buds. They control transpiration by reducing the vegetative growth. In Bougainvillae, Punica granatum and Duranta 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 carundus the terminal bud produces a pair of thorns. They help in protection.
When axillary bud becomes fleshy and rounded due to storage of food, it is called bulbil. It gets deatched from the plant, falls on ground and develops into a new plant. e.g. Dioscorea.
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.