Anatomy Of Flowering Plants - Epidermal Tissue System

The epidermal tissue system bears several specialised cells, and NCERT describes the stomatal apparatus in detail. Each stoma is bordered by two bean-shaped guard cells in dicots, and these guard cells regulate the opening and closing of the pore by changing their turgidity; when they absorb water and become turgid, the pore opens, and when they lose water, the pore closes. Subsidiary cells are specialised epidermal cells that may surround the guard cells and assist them, but they are not the cells that directly bound and operate the pore. Bulliform cells are large empty cells in the upper epidermis of grass leaves that help in rolling and unrolling leaves to reduce water loss, unrelated to stomatal opening. Companion cells are phloem elements associated with sieve tubes for loading sugars, not part of the epidermis. As stated in NCERT Class 11, Chapter 6 (Anatomy of Flowering Plants), guard cells regulate the stomatal aperture. A functional check confirms that turgor-driven control of the pore belongs specifically to the guard cells.