Figure 1.

Gas exchange for photosynthesis and respiration takes place by way of small stoma pores on the surface of plant leaves. (a,b) Stoma apertures are approximately circular with radius a, and a boundary layer of thickness h separates the pores from the bulk atmosphere. The pore-to-pore distance is d = ρ^−1/2, where ρ is the stomatal density. (c) The action of guard cells allows for opening and closing of the pore in response to environmental cues. When fully open pores are often circular in shape with radius approximately one-sixth of the total stoma complex length. Panels (d–h) illustrate the diversity of stoma size and density. (d) Swillingtonia denticulata (image modified from [1]), (e) Aglaophyton major (image modified from [2]) (f) Citrus reticulata, (g) Gossypium hirsutum and (h) Nephrolepis exaltata.