The correct answer is option 2 - Gram. Dumb-bell shaped guard cells are present in the stomata of Gram plants. Guard cells are specialized cells that surround the stomata, which are tiny openings on the surface of leaves that allow for gas exchange. The dumb-bell shape of the guard cells helps control the opening and closing of the stomata. When the guard cells are turgid, meaning they are filled with water, they swell and create an opening for gases to enter and exit the plant. When the guard cells become flaccid, the stomata close to reduce water loss through transpiration. While dumb-bell shaped guard cells are not present in the other options, it is important to note that stomata and guard cells are found in various plants to regulate gas exchange and water balance.