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08 April 1994
Vol 264, Issue 5156

About The Cover

Scanning electron micrograph of stomatal rows from a modern limber pine needle (image width is ˜1 mm). The density of stomata (pores that permit a plant to exchange gases with the atmosphere) of needles from fossil pack rat middens decreased 17% during the last deglaciation, concomitant with a 30% increase in atmospheric CO2. See page 239. [Micrograph: Peter K. Van de Water, Department of Geosciences, and David Bentley, Division of Biotechnology, Arizona Technology Laboratory, University of Arizona, Tucson]