Table 1.

Change in the extent of opening or closure of stomata in epidermal peels of V. faba on O₃ exposure (1.0 μl·liter⁻¹ for up to 3 hr)

Time, hr	Stomatal opening: Mean widths, μm ± SE		Stomatal closure: Mean widths; μm, ± SE
	O3	Air	O3	Air
0	0.5  ±  0.2*	0.5  ±  0.2*	8.1  ±  0.5*	8.1  ±  0.5*
1	−		7.3  ±  0.7	8.1  ±  0.4
1.5	6.4  ±  0.6	7.4  ±  0.7	−	−
2	−	−	6.3  ±  0.6	7.1  ±  0.6
3	8.4  ±  0.5†	10.6  ±  0.6	6.1  ±  0.6	7.0  ±  0.6

Ten stomatal apertures were measured on three epidermal peels for each treatment/time point in each of the six replicates of both opening and closure experiments (total n = 180). 

^*The 0-hr time point represents a set of peels measured before the initiation of treatments. 

^† Significant difference (P < 0.01) between O₃ and air treatment.