The sky darkened, heavy rain began to fall. Gutters overflowed, downspouts spluttered, drains gurgled, busy streets emptied. An umbrella provided some top-down protection from the ferocious cloudburst, but soon it was drenching us from the feet upwards, as raindrops ricocheted from the pavement. We needed to find shelter, quickly.
We took cover in the entrance to Durham’s covered market, and while we waited for the storm to pass there was time to ponder a delightful botanical accident. Water, streaming down the wall from a leaking drainpipe, had created ideal conditions for three species of fern to take root in the wet stonework: strap-shaped leaves of hart’s-tongue, dainty rows of leaflets of maidenhair spleenwort and the intricate fractal fronds of black spleenwort. They must have arrived as airborne spores, invisible to the naked eye, and germinated in moisture from the defective drainpipe. Eventually, fronds unfurled and roots penetrated limey mortar, where an accidental fern garden now flourishes on the pavement edge, as at home in this shady corner of a town centre as it might be beside a Pennine waterfall.
