Last year I met a woman who had just moved into a house with an extraordinary tree, she said—one that grew lemons, limes, and oranges. On the same tree? A backyard citrus bounty is standard practice in Southern California, but generally a yard might have one or two trees with different fruits. You have grapefruits, but no lemons, so you meet your neighbor by asking to pluck some of his. This woman's fruit claim was incredibly exciting, but then she seemed to disappear, and with it my chance to see her tree.