Floral morphology and the development of gamethophytes in Eucalyptus melliodora A. Cunn

Abstract

Flower buds are first recognizable in late December at the commencement of new growth, and the deciduous bracts enclosing each cyme are shed about 3 weeks later. The buds increase rapidly in size, but anthesis does not occur until the end of September and the seeds are not shed from the capsules until the following August. The development of the double operculum and the floral parts is traced. Archesporal tissue is differentiated in the anthers in late February but ovule primordia are not formed until the end of March, by which time the stamens have reached their full size and anther wall formation is well advanced. In each bud events in the anthers and ovules are broadly comparable, but variation in the stages of development occurs between buds on the same branch. Meiosis takes place during the winter months, and embryo sac development follows the Polygonum type. The components of the egg apparatus undergo a threefold increase in size after their formation and, whereas the egg contains little cytoplasm, the synergids become densely cytoplasmic and laterally hooked. The pollen grains are two-celled when they are shed through the slits at the apices of the anthers. A comparison is made of the embryology of E. melliodora and that of species cultivated in Italy and the Black Sea area of the Soviet Union.