Growth and selection of Arabidopsis guard cells on epidermal peels. (A) Rosette of a plant after 19-d growth at the stage from which epidermal peels were taken for impalements. Plants were grown in individual flower pots, covered with a polyester mesh. True leaves are numbered in order of their appearance. Scale bar, 1 cm. (B, C) Epidermal peels taken from plants grown under long- and short-day periods, respectively. Note the higher density of stomata and the smaller size of the epidermal cells in (B). Scale bars, 30 μm. Arrows in (B) indicate examples of guard cell pairs favoured for impalement (D) Stomatal densities of plants grown under long-day (LD) and short-day (SD) (n = 46). The significance level is indicated with asterisks (P < 0.01).