“Muscles” powered by changing humidity apparently help wild wheat seeds reach good places to sprout. Each pointy-tipped seed bears two long, bristly appendages called awns. Scientists at the Max Planck Institute of Colloids and Interfaces in Golm, Germany, found that cellulose fibrils make them expand with humidity, pushing the appendages together, and contract with dryness, pulling them apart. This flexing acts like the swimming stroke of a frog's legs, the researchers say, to propel the seeds along and into the ground. They suggest in the May 11 Science that wheat is optimized for the daily cycle of humidity seen during the dry period (which occurs after the seeds ripen) in the Fertile Crescent, where the crop originated.