Innovations in organismal botany - a tribute to the pioneering studies of Donald A. Eggert
Taylor, Edith , Ryberg, Patricia .
Donald A. Eggert's contributions to the study of fossil phloem structure and evolution.
Phloem tissue is rarely preserved in the fossil record, even in deposits of permineralized or petrified plants. Although several authors had noted the presence of phloem and described the cellular preservation earlier, Donald Eggert was the first to do detailed and modern studies on this tissue and to describe primary versus secondary phloem. Eggert, along with his students, published only three papers on the subject, one each on lycopsid, sphenophyte, and calamite phloem, but he inspired other researchers to take a closer look at phloem in fossil plants, especially in seed plants, and showed that it is possible to infer physiology based on the anatomy of the cells and tissue. His work on the root phloem of the calamite, Astromyelon (with Marion L. Wilson), remains one of the few known examples of secondary phloem produced by a vascular cambium in a pteridophyte and as such, raises interesting questions about the growth and development of these extinct plants. Following Eggert's work in the mid to late 1970s, other researchers have detailed phloem in fossil plants, beginning with Middle Devonian progymnosperms and extending to Cretaceous conifers and bennettitaleans. In the secondary phloem, it appears that the basic cell types and cellular arrangements found in extant seed plants were established early. The bifacial cambium and secondary phloem constructed of sieve cells, phloem parenchyma, and fibers first appear in the aneurophytalean progymnosperms. In the Paleozoic pteridosperms, the same cell types occur, and some examples exhibit repeating tangential rows of alternating cell types, as seen in some modern conifers. Overall, secondary phloem in seed plants appears to be a remarkably conservative tissue through time, perhaps related to the exacting physiological requirements of phloem loading, unloading, and transport.
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1 - University Of Kansas, Department Of Ecology & Evolutionary Biology, 1200 Sunnyside Ave., Lawrence, KS, 66045, USA
Presentation Type: Symposium or Colloquium Presentation
Location: Lindell D/Chase Park Plaza
Date: Tuesday, July 12th, 2011
Time: 3:30 PM