Toxicity levels of mercury, lead, copper, and zinc in tissue culture systems of cauliflower, lettuce, potato, and carrot

Explanted tissues of cauliflower, carrot, potato, and lettuce have been grown in media containing Zn, Cu, Hg, and Pb. Toxicity levels have been established for each of these elements and a considerable uniformity was noted. Lettuce tissue responds occasionally to high levels of Zn by making extraordinarily prolific growth, a matter that has yet to be explained.