Abstract
The red coloration which appears on the leaves of dock plants (R. crispus) after exposure to smog or ozone has been shown to be due to the appearance of an anthocyanin. The leaves of untreated plants do not contain detectable anthocyanin. Furthermore, chlorosis does not occur in treated plants. The anthocyanin was isolated from the leaves of smog treated plants, purified, and identified only as a cyanidin glucoside.