Thanks to a tip from a recent Craig Mod essay - HERE is a superb essay by Annie Dillard from The Atlantic magazine.
A short excerpt:
Down at the root end of things, blind growth reaches astonishing proportions. So far as I know, only one real experiment has ever been performed to determine the extent and rate of root growth, and when you read the figures, you see why. I have run into various accounts of this experiment, and the only thing they don't reveal is how many lab assistants were blinded for life.
The experimenters studied a single grass plant, winter rye. They let it grow in a greenhouse for four months; then they gingerly spirited away the soil—under microscopes, I imagine—and counted and measured all the roots and root hairs. In four months the plant had set forth 378 miles of roots—that's about three miles a day—in 14 million distinct roots. This is mighty impressive, but when they get down to the root hairs, I boggle completely. In those same four months the rye plant created 14 billion root hairs, and those little things placed end to end just about wouldn't quit. In a single cubic inch of soil, the length of the root hairs totaled 6000 miles.