268 STUDIES IN FOSSIL BOTANY 



the estimates of the systematists the Ferns constituted 

 almost exactly half of the total number of species 

 known from the Carboniferous rocks. Now, however, 

 the position has completely changed, so much so that 

 Professor Zeiller, speaking of the Lower Carboniferous 

 Flora, says that the Ferns, " though they were probably 

 not entirely absent, occupied an altogether subordinate 

 rank." * The ground for this radical change of view 

 is to be found in the recognition of a new class of 

 seed-bearing plants, the Pteridosperms, to which, as it 

 now appears, the majority of the supposed Palaeozoic 

 Ferns really belonged. This class coincides in part 

 with the Cycadofilices dealt with in the first edition of 

 this book, but has proved to be much more extensive, 

 and also more remote from the Ferns, than was realised 

 at that time. 



The reduction in the number of the true Ferns 

 becomes more marked, the earlier the period to which 

 we go back. " The Westphalian 2 Flora," according 

 to Professor Zeiller, " is already less rich in true Ferns 

 than the Stephanian, 8 and one might almost raise the 

 question whether in the epochs of the Culm 4 and 

 Devonian, Ferns really existed." The Pteridosperms, 

 in fact, appear to be actually older than the majority 

 of the known Ferns, though certain groups of the 

 latter, such as the Botryopterideae, to be subsequently 

 described, are doubtless of great antiquity. 



From the characters of the frond alone (the part 



1 Zeiller, " Une nouvelle Classe de Gymnospermes : Les Pteridospermes," 

 Rev. Ginerale des Sciences, i6 me annee, 1905. 



2 Middle and Lower Coal-measures. 



3 Upper Coal-measures. 



4 Lower Carboniferous. 



