Stems are also modified to perform different functions. Underground stems of potato, ginger, turmeric, zaminkand, Colocasia are modified to store food. They act as organs of perenation to tide during conditions unfavourable for growth. In plants like watermelon, pumpkins, grapevines stem tendrils developed from axillary buds, are slender and spirally coiled and help the plants to climb. Axillary buds of stems may also get modified into woody, straight and pointed thorns. Thorns are found in many plants such as Citrus, Bougainvillea etc. Thorns protect plants from browsing animals. Some plants modify their stems into flattened (Opuntia), or fleshy cylindrical (Euphorbia) structures. They contain chlorophyll and carry out photosynthesis. Underground stems of some plants such as grass and strawberry spread to new niches and form new plants when older parts die. In plants like mint and jasmine a slender lateral branch arises from the base of the main axis and after growing aerially for some time they grow downwards to touch the ground. A lateral branch with short internodes and each node bearing a rosette of leaves and a tuft of roots is found in aquatic plants like Pistia and Eichhornia. In banana, pineapple and Chrysanthemum, the lateral branches originate from the basal and underground portion of the main stem, grow horizontally beneath the soil and then come out obliquely upward giving rise to leafy shoots.