“…Concerns have been raised regarding this method's reliability (Ko Èrner, 1988;Poole et al, 1996), and it is the purpose of this paper to address these concerns via an extensive analysis of the literature. Analysis includes stomatal responses from fossil observations as well as short-term (experimental, natural CO 2 springs, altitudinal transects, and herbaria) observations, as responses from the latter category are often used to generate standard curves for estimating CO 2 from fossil observations (van der Burgh et al, 1993;Ku Èrschner, 1996;Ku Èrschner et al, 1996;Rundgren and Beerling, 1999;Wagner et al, 1999). Speci®cally, the utility of stomatal indices will be examined, an approach not analyzed in previous reviews Chaloner, 1992, 1994;Woodward and Kelly, 1995).…”