Hello, My dad has a beautiful woodland garden and many of his hostas have small dark dots on top of the leaves. They are raised, not in the leaf so to speak. They feel like running fingers over braille. I’m wondering if you know what they might be, and if they are harmful? The garden is thriving this year with the cooler temps and ample rainfall earlier this season. I should mention most of the hostas with these dots are under silver maple trees.