ABSTRACT
As we noted in the previous chapter, CO2 controls stomatal opening and closing. In addition, it may also control stomatal number (Lake et al. 2001). As we know from books on stomatal physiology (Meidner and Mans£eld 1968), a plant species is characterized by the number of stomata on the upper and lower surfaces of its leaves (Table 9.1). However, this number may not have been always constant due to changing CO2 concentrations in the atmosphere. In this chapter, using data from modern experiments and historical records, we look at the effect of elevated CO2 on stomatal density. Stomatal density is de£ned as the number of stomata per unit of interveinal leaf area (Salisbury 1927). The densities are different on the upper and lower surfaces of leaves, as shown in Table 9.1.
