Electron Microscopy of Mesozoic Megaspores from Denmark

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Abstract
Ultra-thin sections of the mespores Banksisporites pinguis (Harris, 1935) Dettmann, 1961 from the Upper Keuper, Nathorstisporites hopliticus [text not clear]ing, 1958 from the Lias, as well as Margaritatisporites [text not clear]rbanaeformis (Harris, 1961) n.comb., Horstisporites [text not clear]ndalli (Harris, 1961) n.comb. and Istisporites murrayi [text not clear]Iarris, 1961) n.comb. from the Dogger of Denmark were [text not clear]died by transmission electron microscopy. In all of [text not clear]ese megaspores two different sporoderm layers are pre[text not clear]rved in the fossil state. The inner layer (exine) is very [text not clear]in (0.3–2.0 μm) and reveals a lamellated structure [text not clear]rmed by sporonine plates or bands. The outer layer [text not clear]erine) is thicker by far (10–70 μm) and shows dif[text not clear]ent kinds of fine structure formed by sporonine [text not clear]reads. In addition to the sculptural details of the spore [text not clear]rfaces the sporoderm fine structure represents valuable [text not clear]onomic characters. Microspores were ultra-thin sec[text not clear]ned together with the megaspores of Margaritatisporites [text not clear]banaeformis and Nathorstisporites hopliticus. There is [text not clear]ne evidence that, in both cases, megaspore and micro[text not clear]re are derived from the same species. As a general [text not clear]nd the ratio of perine to exine thickness in the sporo[text not clear]ms of megaspores decreases with ascending level of [text not clear]nt evolution.