The isoelectric peroxidase patterns of tobacco tissue cultures allow us to draw inferences to cell elongation and cell division because certain zones in acid pH ranges respond to the influence of auxines and gibberellins (promoting cell elongation) and others respond to the influence of cytokinins (promoting cell division). Stress, due to the absence of phosphate and presence of lead in the medium, causes characteristic changes in the intensity of these sensitive zones in peroxidase patterns. It may be deduced that the increase and decrease of these zones correspond to stimulation and inhibition of cell elongation and cell division, respectively. Cell elongation remains almost unaltered by lack of phosphate but is markedly inhibited by lead, while cell division is enhanced. However, stress brings about a reduction of dry weight. Reactions to stress can be observed earlier in patterns of peroxidase than in growth.