The pattern of gemma/gemmaling ontogeny in the liverwort Cavicularia densa is described from its origin as a primordium within the gemma chamber to the formation of a juvenile gametophyte. Data were obtained from field-grown and axenically cultured plants using a combination of light and scanning electron microscopy techniques. The developmental pattern is characterized by the production of a discoid to ellipsoid, stalked gemma composed of distinct tiers of cells, the central rows of which terminate in latently generative margin cells which originate the occasion of plantlet formation. Gemmaling production results from a generative cell (either an adult apical cell, or a gemmaling initial that transitions into an adult apical cell) that arises from a lateral terminal cell subsequent to quadrant formation. Ultimately, the juvenile gametophyte typical of Cavicularia is produced through the activity of an adult cuneate apical cell. Throughout juvenile gametophyte production, subsequent repetitions of select combinations of primary division sequences along with cytological modifications may continue in the gemma proper. Comparisons with the pattern of receptacular gemma/gemmaling development in Blasia reveal that the fundamental pattern of ontogeny within the Blasiales composes the construction of a tiered gemma bearing latently, generative lateral margin cells and a quadrant system containing the production of a wedge-shaped generative cell responsible for gemmaling construction and ultimately the formation of a juvenile gametophyte through adult merophyte development.
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Vol. 110 • No. 3