Pollen’s energy-efficient water conservation

The outer layer of a pollen-grain wall generally includes apertures through which the grain can gain or lose water. When in an arid environment, pollen grains avoid becoming dangerously dry by undergoing a process called harmomegathy—the grain’s apertures are effectively sealed until the pollen lands in a wetter location. For more than a century, scientists have known that wall structure helps determine the form that a pollen grain assumes after harmomegathy. Now Harvard University’s Jacques Dumais, former Harvard student Eleni Katifori, and colleagues have presented the first quantitative model of the process and confirmed it with electron micrographs such as shown here (the scale bars represent 20 µm). The model incorporates the classic result that stretching a surface costs a lot of energy; instead of stretching, the grain surface bends as the wall folds onto itself to avoid further desiccation. The lily grain in panel a, for example, has an...