Over 1,000 herbarium specimens of the cinnamon fern Osmunda cinnamomea L. from Maryland, New Jersey, and Pennsylvania were assessed for symptoms of foliar ozone injury interveinal bronze necrotic lesions of the pinnules. (Ozone-injury symptomology is based on control-fumigation of live O. cinnamomea plants.) Herbarium sheet inventory included: locale (State and County), collection date (year and Julian day), presence or absence of ozone injury, and percent area of pinnule damaged. (Morphometric analysis of two pinnules sampled from each herbarium sheet was used to obtain estimates of percent area of pinnule damage.) From these data two measures of ozone injury were obtained: (1) % incidence of injury (i.e. number of specimen with necrotic lesions/total number of specimens/ local/decade) and (2) degree of ozone injury, expressed as % area of pinnule damaged. Based on this assessment a decade-by-decade history of ozone pollution from 1850-1990 is constructed. Herbarium specimens from the 19th century show little to no signs of ozone injury (i.e., both % incidence of injury and degree of ozone injury are less than 1%). Thereafter, an irregular but overall progressive increase in the % incidence of injury is detected. The pattern generated is somewhat reflective of historic and economic events of the 20th Century the invention of the internal-combustion engine and the automobile and the First World War, the Depression of the 1930s, the Second World War, the ending of the Second World War with the un-rationing of gasoline, the economic and industrial expansion of the 1950s and 60s, and the Clean Air Acts of the 1960s and 70s. There is a high positive regression correlation of percent area of pinnule-damage as of function of the growing season and no correlation of % pinnule area damage as a function of annual chronology (i.e., average % pinnule area damage/specimen did not change over the years). These findings demonstrate the value of herbarium specimens in the construction of environmental histories.

Key words: environmental history, herbarium specimens, Osmunda cinnamomea, ozone pollution