Diana Galarza, 16, center, and Angelica Lopez, 15, right, answer a customer's question about the hydroponically grown vegetables and herbs they are selling at the Union Square Farmers' Market in New York City, as part of a Cornell Cooperative Extension (CCE) project. The crops were grown by these and other students on the roof of the High School for Environmental Studies in Manhattan using the nutrient drip flow technique developed by Philson Warner, a resource educator for CCE in New York. Caroline Tse/Cornell Cooperative Extension