Ultra-thin sections of the mesporesBanksisporites pinguis(Harris, 1935) Dettmann, 1961 from the Upper Keuper,Nathorstisporites hopliticustext not clearing, 1958 from the Lias, as well asMargaritatisporites text not clearrbanaeformis(Harris, 1961) n.comb.,Horstisporites text not clearndalli(Harris, 1961) n.comb. andIstisporites murrayitext not clearIarris, 1961) n.comb. from the Dogger of Denmark were text not cleardied by transmission electron microscopy. In all of text not clearese megaspores two different sporoderm layers are pretext not clearrved in the fossil state. The inner layer (exine) is very text not clearin (0.3#x2013;2.0 #x3BC;m) and reveals a lamellated structure text not clearrmed by sporonine plates or bands. The outer layer text not clearerine) is thicker by far (10#x2013;70 #x3BC;m) and shows diftext not clearent kinds of fine structure formed by sporonine text not clearreads. In addition to the sculptural details of the spore text not clearrfaces the sporoderm fine structure represents valuable text not clearonomic characters. Microspores were ultra-thin sectext not clearned together with the megaspores ofMargaritatisporites text not clearbanaeformisandNathorstisporites hopliticus. There is text not clearne evidence that, in both cases, megaspore and microtext not clearre are derived from the same species. As a general text not clearnd the ratio of perine to exine thickness in the sporotext not clearms of megaspores decreases with ascending level of text not clearnt evolution.
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