No abstract

Callus and plantlets derived from callus cultures of Nicotiana tabacum var. Wisc. #38 were grown on medium containing serial combinations of gibberellic acid (GA3) and the cytokinin 6‐(3‐methyl‐2‐butenylamino)purine (2iP). Increasing levels of both growth substances resulted in the production of greater amounts of both callus and shoot tissue. More buds were induced when the cytokinin level was increased, and this effect was counteracted by raising the GA3/2iP ratio. Furthermore, the size and form of the shoots depended on the GA3/2iP ratio. High ratios resulted in tall, spindly plants with narrow leaves while low ratios resulted in short shoots with rounded leaves.