Contrary to what one might believe, Ferris didn't immediately understand another Law as soon as he arrived here. He probably also didn't have much experience with plants, which was why he was also taking a long time to understand any Laws related to them.
Gravis looked at all the plants surrounding him and observed them based on their position, not their kind. Gravis wanted to understand a lot of Laws anyway. Concentrating on only a single kind might actually be harder than looking at all of them. By now, Gravis knew very well that a lot of knowledge about one topic might cross into another. Trying to understand the whole thing would be better than understanding only a part of it.
Due to that, Gravis started the long track of understanding Laws.
Two years passed.
"Hey, Gravis! I managed to understand a Law!" Ferris said as he arrived besides Gravis.