Every day an oak tree moves hundreds of gallons of water up from the soil and out, in evaporated form, through its leaves. “Mechanically, it’s a pretty substantial feat,” says Professor Missy Holbrook. “They do it very quietly, with no moving parts, but you’d be hard-pressed yourself to get that much water out of the soil and into the atmosphere.” Learning how plants move water has implications for agricultural productivity, but also for problems in engineering. For several years, Holbrook and her colleagues have studied the long-distance transport of water, as well as sugar, in plants. Some might think of the parallel tubes that transport water and sugar – the xylem and phloem, respectively – as a sort of king’s highway along which the water and sugar travel on mules to their destination. Holbrook conceives of that “road” as highly interactive with the traveling fluids – something of a “smart” road – and including not just mules but clever messengers – ions disguised as royal envoys, and pressure signals as child spies. Plants are brilliant, in this sense: They’ve found mechanical and chemical solutions to problems that so far can’t be reproduced in a lab.