Young floral buds, with sepal primardia only, of both the normal and the male-sterile stamenless-2 (sl\2 /sl\2 ) mutant, were cultured sucessfully on a defined medium. In about 4 weeks, on a relatively simple medium, normal in vitro flower development was obtained in both lines. The medium consisted of Murashige and Skoog's basic salts, White' s vitamins and glycine and sucrose, and was supplemented with benzyl aminopurine (BAP) alone or with both BAP and gibberellic acid (GA\3).
In the normal buds, the initiation and development of the in vitro grown floral organs was comparable to those grown in vivo, although the organs in culture wre slightly shorter at maturity than those developed on the plant. The stamens from the in vitro developed flowers invariably contained microspores and pollen grains. The carpels showed normal development and also contained numerous ovules. Of the various components in the growth medium, BAP was considered by far the most important in the normal development of flower buds in vitro. The presence of GA\3 was not essential for the initiation and development of floral organs, but it did have a promotory effect.
The floral buds of sl\2/sl\2 had a more complex nutrient requirement for the in vitro growth than the normal buds. For example, the concentration of GA\3 needed for sl\2/sl\2 buds was higher than that for normal buds. The in vitro grown sl\2/sl\2 flowers also compared well with those grown in vivo. Some of the flowers also developed external ovules, typical of the sterile stamens of the stamenless-2 mutant. The pistils developed short styles and the ovaries had numerous ovules.
The effects of other cytokinins, gibberellic acid alone, pH, and different concentrations of sucrose, on the in vitro flower development of these two genetically different lines, have also been studied and the results of these experiments will be discussed in detail elsewhere.