Such internal reservoirs help cacti thrive where other plants would instantly wilt. But the saguaro species (Carnegiea gigantea), native to the Sonoran Desert in the United States and Mexico, hides another evolutionary trick. To capture it in action, a park biologist named Don Swann had arrived with an extra-long, custom-made telescoping pole and camera mount system that he extended toward the giant’s crown. Then he snapped several digital photos, the latest in a set of images he’d been taking for several weeks. Later that afternoon, Swann reviewed the time-lapse series and pointed out that “something miraculous” was happening.