Eric Schlosser's writing is marked by the kind of dry, data-filled sentences that kill novels. So it's a good thing he specializes in sobering investigative exposes like 2001's Big Mac-bashing ''Fast Food Nation.'' In his follow-up, Reefer Madness, he sics his dogged investigative yen and fact-wielding pen on three underground economies: pot, migrant workers, and porn. On pot, his litany of official misinformation, unjust persecutions, and draconian laws amounts to a dull, albeit convincing, pro-legalization manifesto. There's more color in his depiction of the laborers in California's strawberry farms, but in the end it too feels like a powerful piece of advocacy. Only in the heftier final section, which views the business of American pornography through the tale of unheralded magnate Reuben Sturman, does Schlosser paint a complete picture, with the nuance and ambiguity of a novel.