describe modification of stem

Modification for food storage: The underground stems of potato, ginger, turmeric, zamikand, Colocasia, etc. are modified for food storage. Such modifications are the tools of perenation to tide over unfavourable conditions.
Modifications for climbing: In some plants, stem tendrils develop form axillary buds. These are slender and spirally coiled structures. A tendril helps the plant to climb to a support, e.g. cucumber, pumpkin, grapevine, etc.
Modification for defence: In some plants, the axillary buds are modified into woody, straight and pointed thorns. Such thorns protect the plant from browsing animals, e.g. Citrus, Bougainvillea.
Modification for photosynthesis: In some plants of arid regions, the stems are modified into flattened or fleshy cylindrical structures. The flattened structure can be seen in Opuntia and the cylindrical structure can be seen in Euphorbia. Such structures contain chlorophyll and photosynthesis happens in them.
Modification for vegetative propagation: Stems are modified for vegetative propagation in many plants, e.g. grass, berry, dahlia, etc.