The large empty colourless cells seen on the upper epidermis in grasses which facilitate the curling of leaves to minimise water loss are

Step-by-step solution

In grasses, certain adaxial epidermal cells along the veins modify themselves into large, empty, colourless cells known as bulliform cells. When the bulliform cells in the leaves absorb water and become turgid, the leaf surface is exposed. When they become flaccid due to water stress, they cause the leaves to curl inwards to minimise water loss. Guard cells regulate the opening and closing of stomata. Subsidiary cells are specialised epidermal cells surrounding the guard cells. Mesophyll cells are the primary sites