The Biology of . . . Flowers

The floor of the Silver Terrace Nursery in the San Francisco Flower Mart is crowded with buckets of long-stemmed roses. They come in more than 40 shades, a glorious sunset’s worth of reds, pinks, oranges, browns, yellows, and whites. And then, like a poke in the eye, there’s electric blue, the sort of color you’d see on a marching band uniform or a high school prom dress.