Gametophyte development in Trifolium pratense L

Abstract

Development of the male and female gametophytes is traced in detail, and departures from the normal sequence of events are found at several points. Among these are pollen abortion, failure of the archesporial cell to develop in the ovule, and collapse of the embryo sac during its development. The formation of two embryo sacs per ovule is of relatively common occurrence, and this is followed by the breakdown of one or both of them. In addition, either the egg apparatus degenerates before fertilization or the nucellar plug may fail to disintegrate and so form a barrier to the passage of the pollen tube through the micropyle. The occurrence of an ovule in which an embryo sac was developing apomictically suggests that a breeding programme based on selection for somatic apospory, rather than high seed yield from sexually reproducing plants, would probably produce a strain of red clover which could maintain itself in pastures.