by Harper & Row, $18.95. Mr. Hobhouse discusses “five plants that transformed mankind,” namely quinine, sugarcane, cotton, tea, and the potato. He concentrates on the commercial, and therefore ultimately the political, results of the widespread use of these substances and finds all of them more or less—mostly more—pernicious. His reasoning is generally persuasive, testy enough to provoke and maintain interest, and occasionally speculative to the point of fantasy. Anyone who suggests that without the arrival of Irish fleeing the potato famine, the United States would have remained solidly Northern European and Protestant has to be dreaming..