Country diary: this is the season for fern sex

Durham city: Minute male capsules on the prothallus burst open, releasing sperm with whiplash tails that swim frantically towards the egg cells

Since humans first began to pile stone upon stone to build walls, and later learned to stabilise them with mortar, plants have taken root in the crevices. They are often ephemeral opportunists, growing from seeds distributed by birds, but for some spleenwort ferns that naturally colonised bare limestone cliffs the crumbly alkaline cement of the manmade alternative offers almost unlimited opportunities.