230 PLANT-LIFE 



with Ferns, are now, after some brilliant researches, 

 proved to have been plants that bore seeds, therein 

 differing from Ferns, which, of course, are reproduced 

 by means of spores. As their name implies, the Pterido- 

 sperms were a group of Fernlike seed-plants; in foliage 

 they resembled Ferns, but the seeds they bore approxi- 

 mated very closely to those produced by Cycads (p. 178). 

 A notable feature of the entire group was that both 

 seeds and male organs, which produced pollen, were 

 borne on leaves in all details identical with ordinary 

 foliage leaves. Thus the sporophylls differed from those 

 of Cycads, which are arranged in conelike flowers. The 

 well-known fossil genera, Alethopteris, Neuropteris, and 

 Sphenopteris, erstwhile classed with Ferns, are now 

 recognized as Pteridosperms. The curious combination 

 of Fern and Cycad characters in this Palaeozoic plant 

 group suggests that in pre-Devonian times a group of 

 simple plants existed, from which the Pteridosperms and 

 Ferns were developed. The Pteridosperms themselves 

 were probably not in a settled condition, but in a state 

 of flux, and might be characterized as a series of experi- 

 ments in plant-life which may have found issue in the 

 Cycad flora important in Mesozoic times, and, later still, 

 in the true Flowering plants. From the vast number 

 of their fossil remains, which are particularly abundant 

 in the Coal Measures, it seems that the Pteridosperms 

 formed one of the leading plant groups in Palaeozoic 

 times. It is possible that the group lingered into early 

 Mesozoic times, since when it has been extinct. The 

 evidence indicates that it reached its most flourishing 

 condition in the Carboniferous Period, and that in 

 Permian times it gradually dwindled. 



