50 AN INTRODUCTION TO THE STUDY OF FOSSILS 



appearance of most of the fossil specimens but on comparison of 

 the internal anatomy when preserved, and on the fructification. 

 These internal molds are marked with longitudinal ribs and 

 furrows, and are jointed, as are the stems of the modern horse- 

 tails. The furrows correspond to the vascular bundles. 



The stems branched and 

 bore narrow, lance-shaped 

 leaves arranged in whorls at 

 the nodes, or joints, of the 

 stem. A single nerve passed 

 from end to end of the leaf. 

 Certain cones described under 

 various names when found 

 separately have been found 

 in connection w^ith a few 

 specimens of Calamites stems. 

 Calamites disappeared in 

 the Permian ; during the 

 Pennsylvanian it was an 

 abundant form in the coal 

 swamps of eastern North 

 America. 



(2) Annularia (Fig. 14), a 

 smaller plant with a stem of 

 two or three inches diameter, 

 and abundant in the Pennsylvanian of eastern North America, 

 is classed with Calamites as a near relative, if it is not actually 

 in some cases merely smaller branches of that form. 



1. What is the name of the only living genus of this order? 

 Describe its appearance. 



2. When in the past did this order include large forest trees ? 

 Name an example of such a tree. 



3. Sketch Calamites, (i) two joints, surface view, (2) cross 

 section. Label joint, leaf bases, position of vascular bundles. 



4. Sketch Annularia; label leaflet. What is its probable 

 relationship to Calamites ? What is its age ? 



Fig. 14. — The ancient horsetail, Annu- 

 laria longifolia Brongniart ( X §), from 

 Pennsylvania, showing seven whorls of 

 leaves. This flourished in the fresh- 

 water coal swamps of eastern North 

 America during the Pennsylvanian time. 

 (Redrawn from Lesquereux.) 



