TUBES that plants use to suck up water can actively divert it to the parts that need it most.
For hundreds of years, biologists assumed these dead-cell pipes, called xylem, passively let water run through. But as Maciej Zwieniecki and his colleagues at Harvard University will report in
In dry conditions, high ion concentrations in the water make hydrogels in the cell walls shrink, pulling open tiny channels to the major pipes. While most plants primarily control their water levels by opening and closing tiny pores in the leaves called stomata, this second system acts as fine-tuning.
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