It’s not easy to get to the National Arboretum in Washington, D.C., without driving. But if you were determined to do so, you’d take the Metro from downtown, then transfer to the B2 bus. There’s no stop at the Arboretum itself, but if you ask the driver whether that bus goes by the institution, as I did, he might pull over anyway and yell back that this is where you have to get off. Either way, you still have to walk about a quarter of a mile down a quiet residential street before you come to the low stone pillars that mark the entrance to the living museum.

If you were determined to make such a trek now, your fuel-saving efforts would be rewarded with Power Plants — a new temporary exhibit that explores flora’s potential to revolutionize… More…