TOUGH ROOTS Dead as a stone? No. These roots live. Quickened by pulsing sun, a tough tree vibrates outer warmth, relays inner strength, feels the tug of stubborn roots. Unflinching under the lash of storms, a tree remembers it held fast when ice catapulted from far north in lightning hails of thunder. Isolated in back acres, concrete cities, stubborn roots stone-contained resist, no matter what machines stutter angrily overhead with great teeth.         Jean McCallion