In a paper published online in advance in Science this week, investigators at the Salk Institute for Biological Studies in La Jolla, Calif., and elsewhere report on their examination of "spontaneously occurring variation in DNA methylation in Arabidopsis thaliana plants propagated by single-seed descent for 30 generations." The Salk-led team observed 114,287 CG single-methylation polymorphisms as well as 2,485 CG differentially methylated regions, "both of which show