52 



AN INTRODUCTION TO THE STUDY OF FOSSILS 



three dots on the lower edge of the scar itself is the severed end 

 of the vascular bundle which formerly passed out through 

 the stem into the leaf, the other two representing strands of 



■par. 



B 



Fig. 15. — The ancient club-moss, Lepidodendron modiilatum Lesquereux, from the 

 coal horizon of Pennsylvania; Pennsylvanian in age. A, surface characters of a 

 small part of a trunk ( X 5). ^, a single leaf-cushion ; natural size. I.e., leaf-cush- 

 ion, — the entire rhombic area except the leaf scar {l.s.) and the base of the ligule 

 {lig.); I.S., scar left by the fall of the leaf; lig., ligule; par., lateral strands of 

 leaf tissue (the parichnos), supposedly here respiratory in function; v.b., vascular 

 bundles, the main tubes for the transfer of sap to leaf and manufactured material 

 back to trunk. (.1 from Lesquereux.) 



leaf tissue. The small triangular dot above the scar has been 

 shown to mark the position of the ligule, a leaf-like organ present 

 in Selaginella and Isoetes, living allies of Lepidodendron. 



Our knowledge of Lepidodendron is based upon fossilized 

 remains of all of its parts. The large trunks have been fcund 

 abundantly in England in such a good state of preservation that 



