This paper provides information on the effects of toxic concentrations of cupric sulphate on the growth of lettuce (Lectuca sativa) seedlings. Root growth is completely inhibited at 5 x 10‐2M and germination stops altogether at 10‐1M. The relative inhibition of root growth is stronger than that of hypocotyl growth. Various metabolites and hormones are partially capable of relieving copper inhibition. Catalase, peroxidase and IAA‐oxidase activity shows increments directly proportional to the concentration of copper. It is obvious that growth is inversely proportional to enzyme activity. The increased level of these enzymes is probably due to an accelerated protein synthesis.

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