270 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1921. 



SECTION OF PALEOBOTANY (FOSSIL PLANTS), EAST WING, FIRST FLOOR, 



NORTH SIDE. 



The exhibition of fossil plants is divided into (1) a biological 

 and (2) a stratigraphic series. Entering this hall from the rotunda 

 (pi. 2, fig. 2), the large upright cases occupying the east end of the 

 hall will be noted to contain the characteristic fossil plants of each 

 geologic formation, beginning with the oldest pre-Cambrian rocks, 

 in which possible plant remains are represented by graphite, and 

 continuing through successively younger and younger formations 

 until the present time. In this series perhaps the most interesting, 

 or at least most unique, is the case devoted to the oldest known life 

 consisting of the remains of algae or seaweeds. These were discov- 

 ered by Dr. Charles D. Walcott in sedimentary rocks preceding the 

 Paleozoic, hitherto believed to be devoid of life, and proved to be 

 the secretions of calcareous seaweeds growing into coral-like plant 

 masses which, by repetition in successive beds, formed thousands of 

 feet of limestone. Thin sections of some of these remains have indi- 

 cated the presence of bacteria at this early date in geologic history. 



The stratigraphic series also contains an exceptionally fine lot of 

 large examples of Coal Measures plants, which contributed so much 

 to the formation of coal beds. Among the large objects forming a 

 part of this series is the base of a trunk and roots of the Carboniferous 

 tree Lepidodendron, one of the ancestors of the present day ground 

 pines or clubmosses. This specimen from the Coal Measures of Penn- 

 sylvania, shows especially well the spreading roots, which were really 

 underground stems adapted to growth in swampj^ places. On the 

 wall at the west end of the hall is a portion of the trunk of this club- 

 moss extending to the ceiling and showing the diamond-shaped scars 

 left by the fallen leaves. These clubmosses often grew to height of 

 100 feet or more. The logs and sections of tree trunks next to this 

 clubmoss stump are of a silicified conifer tree from the Fossil Forest 

 near Holbrook, Ariz. In these trunks the woody matter has been 

 wholly replaced by silica in the form of chalcedony, jasper, and opal. 



In the wall cases along the south side of the hall the exhibits are 

 arranged in biologic order, starting at the far east end with the sim- 

 plest forms of seaweeds and continuing from left to right, like the 

 pages of a book, until the highest forms of flowering plants, like 

 those of to-day are reached. Above these cases are large drawings 

 showing restorations of the landscape of each geological period. 



The amount of material available for exhibition is so large that 

 only a small portion of the more showy specimens can be shown in 

 the space assigned. Thus, for example, the very important Carbonif- 

 erous clubmosses have to be restricted to a single case, in which the 

 space is only sufficient to illustrate with specimens the anatomy of 



