Assertion (A): In grasses, bulliform cells make the leaves curl inwards during water stress.

Reason (R): Bulliform cells are large, empty, colourless cells that become turgid under water stress to minimize water loss.

A is true, but R is false.

The correct answer is Option (3) - A is true, but R is false.

In grasses, certain adaxial epidermal cells along the veins modify themselves into large, empty, colourless cells. These are called bulliform cells. When the bulliform cells in the leaves have absorbed water and are turgid, the leaf surface is exposed. When they are flaccid due to water stress, they make the leaves curl inwards to minimise water loss. The parallel venation in monocot leaves is reflected in the near similar sizes of vascular bundles (except in main veins) as seen in vertical sections of the leaves.