In making his point, Pollan focuses on the relationship between humans and four specific plants: apples, tulips, marijuana, and potatoes. He uses the history of John Chapman (Johnny Appleseed) to illustrate how both the apple's sweetness and its role in the production of alcoholic cider made it appealing to settlers moving west, thus greatly expanding the plant's range. He also explains how human manipulation of the plant has weakened it, so that "modern apples require more pesticide than any other food crop." The tulipomania of 17th-century Holland is a backdrop for his examination of the role the tulip's beauty played in wildly influencing human behavior to both the benefit and detriment of the plant (the markings that made the tulip so attractive to the Dutch were actually caused by a virus). His excellent discussion of the potato combines a history of the plant with a prime example of how biotechnology is changing our relationship to nature. As part of his research, Pollan visited the Monsanto company headquarters and planted some of their NewLeaf brand potatoes in his garden--seeds that had been genetically engineered to produce their own insecticide. Though they worked as advertised, he made some startling discoveries, primarily that the NewLeaf plants themselves are registered as a pesticide by the EPA and that federal law prohibits anyone from reaping more than one crop per seed packet. And in a interesting aside, he explains how a global desire for consistently perfect French fries contributes to both damaging monoculture and the genetic engineering necessary to support it.