In grasses, certain adaxial epidermal cells along the veins modify themselves into large empty colourless cells. These cells are called

Step-by-step solution

In grasses and some other monocots cetain adaxial cells becomes large and colourless known as bulliform cells. When these cells absorbs water and are turgid, the leaf surface is exposed and when they are flaccid due to water stress, they make the leaves curl inward to minimize water loss.