340 PALEONTOLOGY 



as the Hydropteridae are to the Eufilicinae, but they had 

 advanced much beyond merely being heterosporous, and 

 form the first division of the Spermaphyta. 



SPERMAPHYTA. The seed plants again fall into 

 two sub-grades, according to whether the seed is borne 

 on the surface of a sporophyll (Gymnosperms) or in a 

 closed ovary formed by the folding over of one or more 

 sporophylls (Angiosperms). The Gymnosperms include 

 the following five groups. 



1. Pteridospermeae. This extinct group is inter- 

 mediate between the eusporangiate ferns (Marattiales) 

 and the cycads. It is confined to the Upper Palaeozoic, 

 and best known from the fern-like leaves of the Coal 

 Measures. Only of recent years, by the piecing together 

 of evidence from the microscopical structure of petrifac- 

 tions with that from leaf-impressions, has it been possible 

 to discover its true position. Common leaf-genera are 

 Alethopteris and Neuropteris (Fig. 100, g, h), corresponding 

 to the stem genus Medullosa and the seed Trigonocarpmu ; 

 Sphenopteris, to the stem Lyginodendron and the seed 

 Lagenostoma. Other leaves probably belonging here are 

 Glossopteris (Permo-Carb.-Rhaetic, Fig. 100, *) with its 

 rhizome Vertebraria, and the allied Gangamopteris (Permo- 

 Carb.) 



2. Cycadophyta. The modern cycads are a group of 

 plants with palm-like foliage, but much more primitive 

 in their sporophylls than the palms (which are angio- 

 sperms). They are confined to tropical regions, but 

 extend all round the world. Their Mesozoic allies had 



