Ozone: depression of frond multiplication and floral production in duckweed.

Plants of Lemna perpusilla #6746 grown in an environment charged daily with a low concentration of ozone over 2 weeks were slower to begin multiplying, had a significantly lower rate of frond doubling, and required longer to produce fewer flowers than control plants. Treated plants produced smaller, slightly yellow fronds but had no symptoms of acute injury. Control plants produced four times as many fronds and six times as many flowers as plants continuously exposed to ozone (0.1 part per million).