Question

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

• A. Tyloses in vessels
• B. Closure of stomata
• C. Flaccidity of bulliform cells
• D. Shrinkage of air spaces in spongy mesophyll

Answer 1

The correct option is C Flaccidity of bulliform cells

Bulliform cells are large, empty, colourless cells found in the adaxial epidermis of grasses.

These cells absorb water and become turgid due to which the leaf surface is exposed.

However, during dry weather, these cells become flaccid due to water loss. This causes the leaves to curl inward to minimise loss of water. Leaf rolling may augment stomatal closure.

Tyloses are balloon-­like extensions of parenchyma cells that protrude into the lumen of adjacent xylem vessels through a pit in the cell wall. Most commonly, tyloses are formed in older woody tissues, likely in response to injury. Gradually, they block the vessels and hence help prevent the spread of fungi and other such pathogens inside the plant.

Shrinkage of air spaces in spongy mesophyll tissue of leaves results in decrease in buoyancy of plants.