1. _Foerstia._ These fossils may be the earliest known occurrence of bryophytes, although some authors have referred them to the brown algae. After Dawson. 2. _Psilophyton._ A primitive vascular plant. After Dawson. 3. _Lepidodendron._ After Hirmer. 4. _Sigillaria._ After Hirmer. 5. _Calamites._ After Hirmer. 6. _Sphenophyllum._ After Fuller and Tippo. 7. _Equisetum._ The only living genus of scouring rushes. After Fuller and Tippo. 8. _Megaphyton._ An ancient true fern. After Hirmer. 9. Modern tropical tree fern. After Fuller and Tippo. 10. _Medullosa._ An ancient seed fern. After Stewart. 11. _Williamsonia._ An extinct cycad-like tree. After Sahni. 12. _Cycas._ A modern cycad. After Chamberlain. 13. _Baiera._ A fossil leaf genus of ginkgo, whose only living representative is the species _Ginkgo biloba_, saved from extinction by careful cultivation in China. Several specimens of this “living fossil” were presented to this country by the Chinese and are now flourishing on many college campuses, including that of the University of Illinois. After Mägdefrau. 14. _Cordaites._ After Grand Eury. 15. _Lebachia._ A “transition conifer,” forerunner of present day conifers. After Mägdefrau. 16. _Pinus._ Modern pine. After Mägdefrau. 17. _Acer._ Common maple, an angiosperm whose leaves are also found among Tertiary fossils. After Mägdefrau. 18. _Rosa._ The prairie rose, an angiosperm. 19. _Campsis._ Trumpet vine, an angiosperm. [Illustration: _Geologic Time Chart_]