5] EVOLUTIONARY DEVELOPMENT AND PAST HISTORY 139 



suggest primitive Angiosperms. The Gnetales may perhaps have 

 sprung from the same stock ; but such fossils of them as are known 

 are relatively modern, and so the origin and relationships of this 

 group remain obscure (in Fig. 37 it is left near the Angiosperms). 

 The Mesozoic has often been called the era of Cycads, owing to 

 the presence in its deposits of some Cycads and of many more 



Fig. 33. — Pteridosperms (reconstructed). A, Lyginopteiis oldhaniia (after Berry) 

 (x about vo); B, Splieiinpteris tenuis, portion of leaf with seeds (after Halle) 



( X i). 



Cycad-like Gymnosperms (Cycadeoidales) which between them com- 

 prise the Cycadophytes. The living Cycads (an example is illus- 

 trated in Fig. 18, A) are apparently the relics of a once more important 

 and widespread group, whereas the Cycadeoidales have long been 

 extinct. By many authors the Cycadeoidales are kept as a separate 

 group, also called the Bennettitales, on account of their remarkable 

 reproductive structures that were apt to look more like flowers than 

 cones (a reconstructed example is shown in Fig. 34, A) ; others were 

 slender and branching but probablv never very big. The Cycado- 

 phytes presumably arose from pteridospermous ancestors during the 

 late Palaeozoic, the living Cycads supposedly representing the end 

 of a line that in most respects has changed little since the early 



