Hydroponic Lettuce Rows in a Greenhouse

The word hydroponics was coined in the 1930s from the Greek words for water and work. Plants grown this way get their food from water flowing past the roots instead of from soil. In this hydroponic lettuce jigsaw puzzle, leafy heads sit in neat holes along white channels in a greenhouse, with water splashing from a return pipe at the end. Green streaks of algae on the plastic show the system has been running for a while.