Ovule Ontogeny and Its Relation to Seed-Coat Structure in some Species of Polygala (Polygalaceae)

The ovule primordia of Polygala are trizonate. The inner integument is two layered and of dermal origin. The outer integument can be two- to multilayered. The changeover from a subdermally initiated outer integument to a mainly dermal outer integument is clearly demonstrated. In P. chamaebuxus, the outer integument is mainly of subdermal origin, whereas in P. vulgaris the subdermal contribution to the outer integument is delayed and restricted to the antiraphal side. The differences in ontogeny are reflected in the seed-coat structure. The exostome aril arises from the dermal apex of the outer integument and is completely of dermal origin.