Invincibly Established

“Some twenty years ago an acorn dropped Into a rocky ledge where limestone showed A few white teeth and where the forest stopped Before the red slash of a quarry road. It had no business to be hatching there, A skinny leg of green life on the bare, Inhospitable ledge.  A week, no doubt, Would see it shrivel up and starve itself, A pinch of failure in a cup of stone. But there it stands today upon its shelf,  Its talons in the rock! I freely own The whole thing baffles me, and I...