Different aerial modifications shown by stem are as follows:
1. Stem tendrils:
a. Tendrils are thin, wiry, photosynthetic, leafless coiled structures.
b. They give additional support to developing plant.
c. Tendrils have adhesive glands for fixation.
d. Apical bud in Vitis quadrangularis gets modified into tendril. The further growth is carried out by axillary bud.
e. In Passiflora axillary bud gets modified in tendril.
f. Extra axillary bud is the one which grows outside the axil. This bud in cucurbita gets modified into tendril.
g. Normally floral buds are destined to produce flowers. But in plants like Antigonon they produce tendrils.
2. Thorn:
a. It is modification of apical or axillary bud.
b. Thom is hard pointed and mostly straight structure (except Bougainvillea where it is curved and useful for climbing).
c. It provides protection against browsing animals and also helps in reducing transpiration.
d. Apical bud develops into thorn in Carrisa whereas axillary bud develops into thorn in Duranta, Citrus, Bougainvillea, etc.
3. Phylloclade:
a. Modification of stem into leaf like photosynthetic organ is known as phylloclade.
b. Being stem it possesses nodes and internodes.
c. It is thick, fleshy and succulent, contains mucilage for retaining water e.g. Opuntia, Casuarina (Cylindrical shaped phylloclade) and Muehlenbeckia (ribbon like phylloclade).
4. Cladodes:
a. The branches of limited growth i.e. one intemode long and performing photosynthetic function are called as cladodes.
b. True leaves are reduced to spine or scales to reduce rate of transpiration, e.g. Asparagus.
5. Cladophylls: These are leaf like structures bore in the axil of scale leaf. It has floral bud and scale leaf in the middle i.e. upper half is leaf and lower half is stem. e.g. Ruscus.
6. Bulbils:
a. In plants like Dioscorea, etc. axillary bud becomes fleshy and rounded due to storage of food called as bulbil.
b. When it falls off it produces new plant and help in vegetative propagation.
