If he wasn't wrong, then plants took in raw mana from the atmosphere, then processed it, before it was released as the lights. The humans probably absorbed this processed mana during their sleep or rest, and used it to replenish their own mana when it was depleted.
This was just a conjecture, of course. Reeve didn't know how the plants could take in raw mana and process it before releasing it in an elemental form … like fire for example.
"Good, it seems some of you have managed to sense it", said the professor, his gaze looking at Reeve, who was busy wondering how mana really worked.
After what seemed like an eternity, but in reality, was only five or so minutes, all the students were glowing with either a brown glow, or a green one. The professor seemed satisfied, judging by the smirk on his face.
He spoke, "Now that you can sense mana flow, the next step is to channel the mana into the mana veins in your hands. In order to cast a spell, you should be able to channel the mana into whatever medium you want to use to cast the spell. For example …"
Before waiting to see if the students had understood anything, the professor raised his right hand, and then slammed it on the ground in front of him. Instantly, a wall made of stone rose up between the professor and the students. The stone wall was less than two meters tall. In fact, it was the size of the average adult.
"This spell is called Stone Wall. It's the most basic defensive spell which you're supposed to master during this semester. In order to pass my class, you should be able to make a wall covering two meters in length and height!"
As usual, the pattern among the students repeated itself. It started with gasps, followed by murmurings, and then ended in complete silence.
Reeve, as usual, was seeing things. He thought he was hallucinating, as he normally does, when he saw the lights coming from the professor's hand, forming a brown rune inside the professor's palm. When the professor slammed his hand onto the ground, there was a slight glow, followed by a stone wall rising from the ground.
"Now, to cast this spell, you need to know the rune for the spell. When you know the rune, you channel mana into your palm, where the rune will be, and then touch the ground. The amount of mana you channel into the rune will determine the length and width of the wall. Now, here's what the rune looks like", the professor explained, taking a notebook and pen.
He began by drawing the rune that Reeve had seen. When he had finished, he passed the drawing to all the students.
Someone raised their hands, and after the professor nodded, they asked, "How come we didn't see the rune when you raised your hand?"
"That's because I concealed it. Advanced mages can conceal the runes, so that the person they are fighting doesn't guess what sort of spell they're trying to cast. Imagine if someone wants to cast a fireball for example. If you know the rune, then you will know what the weaknesses of the spell will be, which in turn allows you to prepare against the spell. However, if someone just cast the spell without anyone seeing the rune, they won't be able to tell what kind of spell is being cast, until the spell has materialized. Do you understand?"
The student looked confused, which prompted the professor to let out a light sigh. He continued, "Anyway, I concealed the rune out of habit. What I need you to do, is to form the rune I gave you using your will. Close your eyes again, and then visualize the drawing in your palm."
All the students, including Reeve, closed their eyes and did as they were told. Of course, nothing worth noting happened.
"While you're visualizing the drawing in your head, try to imagine the rune already drawn on your palm", there was a pause, before the professor continued, "Now, I want you to try to move the mana into the direction of your palm. It might take some time, but be patient. If you're feeling a little light headed, stop immediately!"
Reeve could see a light brown rune on his palm, like a tattoo imprinted there. After hearing the professor telling them to move their mana, Reeve focusing on trying to direct the mana flowing inside his body towards his palm. Initially, the mana was too faint, but right now, it started flowing like a mighty river into the veins in his hands. Reeve didn't know how he was doing it, but he could hear the faint roar of a mighty river.
The tattoo of the rune in his palm began to glow, and without waiting for anyone to tell him, he hurriedly slammed into the ground in front of him. He was afraid of losing control, as the mana was moving too fast.
As he slammed the ground, he expected to see a giant wall of stone rising up. However, contrary to his expectations, a small wall, less than thirty centimeters in both length and height, rose up into the air. Reeve could not hide his excitement! He was finally able to learn a magic spell!
Of course, the rising of the small stone wall attracted gazes from not just the students, but the professor as well.
"Oh… It seems someone has managed to grasp the concept on the first try!" announced the professor, which Reeve thought was unnecessary, since everyone could see it for themselves.
There were all sorts of gazes directed at Reeve at this moment. In these gazes, there was jealousy, envy and even hostility. However, Reeve tried his best to ignore these gazes.
"You've wasted a lot of mana in casting this spell, which is why it's only this small. However, with practice, you should be able to cast a wall which is much wider", spoke the professor. He continued, "Everyone else, continue trying to cast the spell!"