2 Edwards D, Kerp H, Hass H (1998) Stomata in early land plants: an anatomical and ecophysiological approach. J Exp Bot 49: 255–278.
3 McElwain JC, Chaloner WG (1995) Stomatal density and index of fossil plants track at mospheric carbon dioxide in the Palaeozoic. Ann Bot 76: 389–395.