The structure and growth of the seedling, as described in the literature, is discussed for both monocotylar Dicotyledones and for Monocotyledones (several Apiaceae, Ranunculaceae and Gesneriaceae; species of Combretum, Peperomia, Cyclamen, Corydalis and Pinguicula, and also anomalous syncotylar examples of Impatiens, Butomus, Agave, Cordyline, Dioscorea, Pitcairnia and Costus). In all examples the single cotyledon appears to be derived, phylogenetically, from an ancestral pair which has fused, often with no remaining trace of their double origin, to give an apparatus which buries the unexpanded plumule and radicle deeply in the ground early in germination. No evidence for suppression of one of the ancestral pair of cotyledons was found in any species.
The syncotylar theory of the origin of monocotyledons of Sargant (1903) is supported and extended to apply to all known monocotylar species. The anomalous appearance of paired cotyledons in Agapanthus and Cyrtanthus apparently results from twinning, as known in Sinapis and Centranthus, not to atavistic reformation.