Almost all American vegetables were brought here by immigrants. By now some have spent many generations with one family on one plot of land. They have become heirlooms—living heirlooms that adapt in an elegant way to their own microclimate. Imagine, for example, that your great-grandfather ate a particularly huge, particularly sweet tomato of a variety pollinated by the wind and insects. He saved the seeds to plant the following year. He and his children and grandchildren repeated this process for a hundred years or so. The result? More big, sweet tomatoes and fewer small, bitter ones—and heirloom seeds worth saving.