Two tree facts, one embarrassing and one surprising:
What gives a tree mass, what is it made of? It is not the nutrients from the ground. Otherwise, there would be a hole under every tree. This was my first answer.
I should and did know the answer to this, but could not get there.
Then: There is no one theory on how water travels from the roots to the leaves. There are many, and disagreement on which one is right.
This one I assumed I had an answer for but did not. Since no one fully does.
In two tree facts, I learned how much I assume.