ORIGIN AND DEVELOPMENT OF FLORAL BUDS IN TOBACCO EXPLANTS.

Initiation and formation of floral buds was studied on explants of Nicotiana tabacum. During the first stage of development (0 to 4 d), protrusions are formed at the basal side of the explant as a result of cell divisions in both sub-epidermal and epidermal cell layers. The second stage (4 to 7 d) is characterized by the formation of tracheary centres inside the protrusions followed by the formation of floral primordia at the surface of the protrusions. These primordia result from both epidermal and sub-epidermal cell divisions. In the final stage (7 to 15 d), flower primordia develop into flower buds and tracheary elements grow into the buds. Polarity present in cells of freshly cut explants is lost within a few days after the onset of the experiment. After 4 to 7 d, a new polarity axis has differentiated inside the protrusion. This axis runs from the tracheary structure inside the protrusion to the flower primordium at the periphery.