Light

"Follow me, young acolyte." The grand magus Yvere said. 

Even though Emery had no idea why the grand magus wanted to speak with him personally, he followed him without a second thought.

With gentle guidance, the grand magus led him to one part of Elder's respite place, a garden outside that received a lot of natural light and air.

In the next moment, he walked towards one corner and came to a complete halt right in front of a certain type of flower with some purple petals. The grand magus looked at Emery, while pointing to two saplings among them. 

"Can you grow the sapling with your best spell?" Asked the grand magus. Emery nodded and immediately proceeded to do what was asked.

He had the [Acell growth] spell to grow the sapling, but if he wanted to give his best, that would be the [Photosynthesis] spell. He just needed to control the spell, not to make drastic changes to its cell. Right after, the sapling grew to be 2 meters tall.