剑桥词典on a leaf , one of a pair of cells positioned around each stoma (= a small hole in the surface ) that open it to release gases or close it to prevent water from being lost 植物的保衛細胞（保衛細胞組成環狀，搆成了葉子的氣孔，能控制氣流的進出，阻止水分流失。） 返回 guard cell