Bulliform cells are bubble shaped epidermal cells, generally they are large in size.
They are found in groups above the surface of leaves in many monocots.
Bulliform cells are large , empty and colourless present near the mid vein of the leaf.
In Monocot leaves bulliform cells can be seen within the upper epidermis.
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Functions of bulliform cells:
When there is plentiful water, leaves absorb water and bulge and shrink ,when there is scarcity of water, leaves start curling which prevents the loss of water occurring through evaporation.
When conditions are unfavourable for leaves, bulliform cells roll leaves to prevent water loss through transpiration.
Bulliform cells have control over the transpiration process. They also unfurl the leaves in appropriate conditions.
Bulliform cells are generally found in grasses.
Final Answer
Hence , bulliform cells are large bubble shaped cells, present on the adaxial (top) surface of the leaf. They help the leaves to survive in unfavourable or stressful conditions by curling or rolling of leaves.