Joanne Silberner

From the front door of the glass-walled gift shop at the Alnwick Garden in the far northeast of England, the scene looks innocent enough. A sapphire green English lawn slopes gently downward, toward traditional, ornamental gardens of rose and bamboo. Across the small valley, water cascades down a terraced fountain.

But a hundred or so plantings kept behind bars in this castle's garden are more menacing — and have much to tell visitors about poison and the evolutionary roots of medicine.