6o AN INTRODUCTION TO THE STUDY OF FOSSILS 



from the slenderness of its stem in proportion to its length and 

 from the presence of spines on stems and leaves. 



Fragments of the stems and leaves of this plant occur very 

 abundantly and in well-preserved condition in the calcareous 

 nodules or coal balls of the English Carboniferous coal deposits 

 mentioned above. 



The plant has very nearly the stem structure of a cycad, but 

 a fern-like leaf. Highly organized seeds have been found in a 

 definite connection with this leaf, which shows that Lyginoden- 

 dron, instead of being a fern as was formerly supposed, was a 

 seed-plant. It was still, however, a very primitive seed-plant 

 for both seeds and pollen sacs were borne on slightly altered 

 portions of the ordinary leaf. Lyginodsndron is thus seen to 

 be a noteworthy example of synthetic types, that is, of forms that 

 combine characters which afterward separate and distinguish 

 separate orders. 



1. What is the chief distinguishing characteristic of the 

 Spermatophyta ? How is this indicated in the name itself ? 



2. Describe the formation of the sporophyte and the game- 

 tophyte stages in the spermatophytes. 



3. Into what subdivisions are the spermatophytes divided ? 



4. What is the difference between a gymnosperm and an angio- 

 sperm ? Show that this difference is indicated in the derivation 

 of the name. Name three common living gymnosperms. 



5. Into what orders are the gymnosperms divided ? 



6. What are the Cycadofilicales ? In what respect do they 

 resemble ferns ? How are they like cycads ? When were 

 they most abundant ? Name an example. 



7. Sketch a Neuropteris pinnule. How is it known that 

 this is not a fern ? 



8. For what is Mazon Creek famous ? 



9^ In what respect is Lyginodendron a synthetic type ? 



Order B, Cycadales 



Family i, Cycadeoidece. — This extinct family of trees or 

 shrubs resembled the living cycads in general outer appearance. 



