Select the correct pair.

To identify the correct pair, let us analyze each of the options in detail:

1. Large colorless empty cells in the epidermis of grass leaves - Subsidiary cells
Incorrect: Large, empty, and colorless cells found in the upper epidermis of grass leaves are called bulliform cells (or motor cells). They help the leaves roll or unroll to control water loss. Subsidiary cells are specialized epidermal cells that lie adjacent to the guard cells of stomata.

2. In dicot leaves, vascular bundles are surrounded by large thick-walled cells - Conjunctive tissue
Incorrect: In dicot leaves, the vascular bundles are surrounded by a layer of large, thick-walled cells known as the bundle sheath. Conjunctive tissue is the parenchymatous tissue that lies between the xylem and phloem in roots (specifically in the stele of roots).

3. Cells of medullary rays that form part of cambial ring - Interfascicular cambium
Correct: During secondary growth in dicot stems, the parenchymatous cells of the medullary rays located between the vascular bundles (adjoining the intrafascicular cambium) become meristematic. These cells form the interfascicular cambium. Together with the intrafascicular cambium inside the vascular bundles, they form a complete, continuous ring of vascular cambium.

4. Loose parenchyma cells rupturing the epidermis and forming a lens-shaped opening in bark - Spongy parenchyma
Incorrect: In woody trees, the phellogen (cory cambium) cuts off closely arranged parenchymatous cells on the outer side, which soon rupture the epidermis to form lens-shaped openings called lenticels (which facilitate gaseous exchange). Spongy parenchyma refers to the loosely arranged photosynthetic cells with air cavities located in the mesophyll of a leaf.

Therefore, the only correctly matched pair is: Cells of medullary rays that form part of cambial ring - Interfascicular cambium.