Grass leaves curl inwards during very dry weather. Select the most appropriate reason from the following:

Q. Grass leaves curl inwards during very dry weather. Select the most appropriate reason from the following:

1. Tyloses in vessels
2. Closure of stomata
3. Flaccidity of bulliform cells
4. Shrinkage of air spaces in the spongy mesophyll

Answer: Flaccidity of bulliform cells

Bulliform cells are large, bubble-shaped epidermal cells that occur in groups on the upper surface of the leaves of many monocots.These cells are present on the adaxial or the upper surface of the leaf. They are generally present near the mid vein. These cells are large, empty and colourless.

Bulliform cells are the cell distributed between the epidermal cells of the leaf. They are responsible for the storage of water. Bulliform cells help in rolling of leaves to prevent loss of water through transpiration during stress conditions. Hence they regulate transpiration process.

During drought, the loss of water through vacuoles induces the reduced bulliform cells to allow the leaves of many grass species to close as the two edges of the grass blade fold up toward each other. Once adequate water is available, these cells enlarge and the leaves are forced open again.