Mechanical Support and orient the leaves in a manner that they are exposed to maximum sunlight and for efficient gaseous exchange during photosynthesis and respiration. They also bear flowers and fruits.
Conduct water and minerals from to leaves and manufactured food from leaves to different parts of the plant. The stem conducts water and minerals from the root to the leaf.
Food storage – underground modified stems, it serves as a storehouse of food material, stems store food and water in plants e.g., potato, ginger, onion etc.
Water storage – In many fleshy stems of cacti and euphorbias water is stored in sufficient quantity that is used by the plant in extreme dry conditions.
Photosynthesis – the young green stems and the modified stems of many cacti and other fleshy plants manufacture food material in the presence of sun light with the help of chloroplasts present in them.
Protection – Several modified stems into thorns protect the plants from grazing animals e.g., citrus.
Perennation – Several modified underground food laden stems also serve as perennating organs, e.g., potato, ginger, onion etc.
Vegetative propagation – Several aerial, sub-aerial and underground modifications of the stem help in vegetative propagation, e.g., runner of doob grass, sucker of mint and setts of sugarcane.
Climbing – Tendrils or hooks are modified branches or buds. They coil around the support and help the plant to climb e.g., grape vine.