Fig. 10. Comparison of metabolic limitation in three species having low Ψ_w. The limitations are entirely metabolic because in Fucus vesiculosus no stomata are present and photosynthesis occurs in the tissue surface (from Kawamitsu et al., 2000), while in the leaves of Primula palinuri and Helianthus annuus the epidermis is peeled away and the stomata have been removed [from Dietz and Heber (1983) and this paper].