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标题：Ultrastructure and cytochemistry of Miocene angiosperm leaf tissues
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作者：Karl J. Niklas ; R. Malcolm Brown ; Richard Santos 等
期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1978
卷号：75
期号：7
页码：3263-3267
DOI：10.1073/pnas.75.7.3263
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Angiosperm leaf fossils (16.7-25 x 106 years by potassium/argon dating) referable to Zelkova were isolated from pyroclastic deposits in the Succor Creek Formation, Oregon. These fossils reveal a three-dimensional structure in mesophyll cell layers and vascular bundles, while transmission electron microscopy of fixed tissues reveals well-preserved chloroplasts with grana stacks and starch, as well as nuclei with condensed chromatin. Transmission electron microscopy indicates that cell walls retain a cellulosic microfibrillar architecture, while ultrastructural and cytochemical confirmation is presented for chloroplast starch and the presence of native cellulose. The preservation of cell walls and cytologic structures in fossil materials of this age indicates an unusually mild fossilization process attending the post-depositional maturation of associated sediments. The preservation observed appears to be associated with rapid physical dehydration coupled with endogenous fixation by organic acids (possibly tannins and/or chlorophyll derivatives).
关键词：angiosperm paleobotany ; cytology ; electron microscopy ; histochemistry ; evolution