Answer:
What has roots that nobody sees and is taller than trees. Up up up it goes and yet never grows?
I begin your sentences.
I will disappear every time you say my name. What am I?
Turns me on my backs and open up my stomach. You will be the wisest of men though at start a lummox.
I go up when the rain comes down. What am I?
Whoever made me don't want me. Whoever bought me don't need me. Whoever use me don't know me.