Observations on Carboniferous seeds of Mitrospermum, Conostoma and Lagenostoma

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Abstract
Synopsis: Mitrospermum bulbosum sp. nov. is described from a single specimen found in the Lower Carboniferous Cementstone Group of Berwickshire. It is a platyspermic seed about 14 mm diameter. The nucellus is free from the integument laterally and contains a single megaspore above which is a pollen chamber and well-developed apical beak. The integument is cordate at the base around a bulbous chalazal region with two membranous wings which terminate above as two flat lobes having a V-shaped sinus between. At the base of this sinus is the micropyle which surrounds the apex of the nucellar beak.Mitrospermum compressum Arber has been re-investigated from 21 specimens and evidence adduced to show that the micropylar canal expands upwards and opens between two short apical lobes.Conostoma oblongum Will, has been re-investigated from 20 specimens. It possesses four integumental bundles; sometimes there are two basal lobes but no integumental flanges; no free apical lobes have been seen and the seed was sessile, not having a wide pedicel.A specimen of Lagenostoma ovoides Will, with a mature prothallus is briefly described from longitudinal sections. At the upper end the prothallus has three archegonia and a circular trough surrounding the ‘tent-pole’.