Further Studies Concerning Stomatal Diffusion

Abstract

Diffusion through single- and multipore membranes was measured by sealing special metal membranes over vials of water and determining losses gravimetrically. Diffusion through single pores in thin membranes was directly proportional to pore diameter. Pores 2.5-80[mu] were used, with spacing varying from 10 to as many as 160 pore diamters. With a spacing of 10 diamters uniform evaporation of 70-80% of a free water surface was obtained through pores 5-80ji in diameter, spaced 50-80^. Diffusion through individual 5[mu] pores was reduced 98% by the interference of the surrounding pores. When pores 2.5-20[mu] were uniformly spaced at 200[mu], the smallest pores, with an area 1.6% of the largest, carried 35% as much diffusion, the result of the diameter effect and of decreased interference in pores now 80 diameters apart. Wind increased diffusion by increasing the gradient, but did not change the basic responses of small (<100[mu]) pores when diffusion shells were present below the pores. When the membranes were placed directly on wet filter paper, wind increased diffusion to diameter proportionality in multipore membranes.