The gas that enters through the holes in leaves is carbon dioxide (CO2). These holes are called stomata.

Here's a bit more detail:

* Stomata are tiny pores on the surface of leaves, usually on the underside.

* Guard cells surround each stoma and control its opening and closing.

* Carbon dioxide is essential for photosynthesis, the process by which plants create their own food.

* Oxygen is a byproduct of photosynthesis and is released through the stomata.

Let me know if you'd like more information about stomata, photosynthesis, or any other plant processes!