Relationship of stomatal density and index of Salix cinerea to atmospheric carbon dioxide concentrations in the Holocene

The impact of different concentrations of ambient CO 2 on the stomatal density and index of Salix cinerea are investigated. Fossil leaves (AMS dated 9190 BP) and present-day material from the same site in south west Ireland are compared with nineteenth-century herbarium material from Ireland. Techniques for obtaining reliable counts of stomata and epidermal cells from hairy leaves with sunken stomata are reported. Stomatal density and index were both found to be inversely related to CO 2 concentration. The data also demonstrate the higher intra-specific variability of stomatal density over stomatal index. Analysis of the data indicates that similar investigations should be confined to single sites.