UNSURPRISINGLY, Frank Keppler and Thomas Röckmann's February article on the discovery of methane emissions in plants elicited strong reactions. Although some correspondents seemed eager to jump to the exact global warming--denying conclusions Keppler and Röckmann had cautioned against, others expressed a more thoughtful attitude as to how this discovery might affect our understanding of global climate change. Readers were also drawn to the more cosmic implications of Christopher J. Conselice's overview of how scientists believe dark energy shapes the universe. Many were unsatisfied with our inability to detect such a force from anything but its effects and offered their own theories as to what dark energy might tangibly represent or how the universe could function without it.

DENTAL DELIMITATION
"License to Work" [News Scan], by Rodger Doyle, suggests that the reason the number of dentists in the U.S. has not grown substantially compared with other professions is restrictive licensing practices. Doyle has the cart before the horse. The license to practice dentistry is obtained after the completion of educational requirements and is typically passed by most dentists, although it sometimes calls for more than one attempt. The restriction on numbers is at the beginning of the road, where the educational system has not changed the number of dentists it is capable of training on average since the 1970s. This restriction is not caused by the licensing board but by the cutting of direct and indirect federal and state support for dental education (number of schools, class size, faculty numbers, student loans, and so on).