Describe modifications of stem with suitable example

Modifications of Stem : The stems are modified to perform different functions:
1.Underground stems of potato, ginger, turmeric are modified to store food in them. They also act as organs of perenation to tide over conditions unfavourable for growth.
2.Stem tendrils which develop from axillary buds, are slender and spirally coiled and help plants to climb such as in gourds (cucumber, pumpkins, watermelon) and grapevines.
3.Axillary buds of stems may also get modified into woody, straight and pointed thorns. Thorns are found in many plants such as Citrus, Bougainvillea. They protect plants from browsing animals.
4.Some plants of arid regions modify their stems into flattened (Opuntia), or fleshy cylindrical (Euphorbia) structures. They contain chlorophyll and carry out photosynthesis.