INTRODUCTION 497 



fossils? It will be shown in detail" below that at least three types, which 

 may reasonably be held to have been true Ferns, were represented in the 

 Primary rocks, viz. the Botryopterideae, the Pecopterids of the group 

 Cyatheites of Goeppert, 1 and also certain forms allied to some of the 

 lowest Leptosporangiates, though there is some room for doubt how 

 nearly they coincided with these. 



On the question of detailed proof of the homosporous nature of these 

 plants the reply for a given case has been supplied by Scott. He has 

 found in the sporangia of Stauropteris Oldhamia, a fossil referred to the 

 Botryopterideae, that the spores may germinate within the sporangium, 

 just as they may be found to do in Todea, Trichomanes, and some other 

 living homosporous Ferns. This leaves little room for doubt that the 

 mode of reproduction of Stauropteris Oldhamia was essentially that of a 

 true Fern. 2 But it is not to be expected that such evidence will be 

 available in every case : nor indeed should it be considered necessary. 

 The fact that such proof is accessible, even in a single instance, comes 

 as a wholesome corrective to that tendency, which followed on the first 

 discovery of Pteridosperms, to regard all Palaeozoic Ferns as potential 

 Seed-Plants. The converse will, however, be the more natural position 

 for those who view the new facts calmly, viz. to hold all Fern-like fossils 

 as true Ferns until their character as Pteridosperms is proved. The 

 question is mainly one of the state of advancement reached by any given 

 fossil, for it may be presumed that the Pteridosperms sprang ultimately 

 from a homosporous Fern-like ancestry. The onus probandi lies with 

 those who are disposed to accord to any given fossil the more advanced 

 position, however readily others will accept the proof as it becomes 

 available. On this footing the Pecopterids, as limited above, together 

 with the Botryopterids, and some others, may for the present be held 

 to be Palaeozoic Ferns of the homosporous type, of which the life-history 

 was in all probability essentially the same as that seen in modern 

 Ferns. The early existence of homosporous Ferns, which evolutionary 

 theory would suggest, or even demand, appears on the basis of Palaeo- 

 phytological evidence to be beyond any reasonable doubt. But they 

 are now recognised as bulking less largely in the early Flora than was 

 once believed to be the case. 



According to the arrangement and succession of development of their 

 sporangia the homosporous Ferns have been divided into three series : 3 

 the Simplices, in which the sporangia of a sorus are produced simultaneously : 

 the Gradatae, in which there is a definite succession in time and space 

 in their production : and the Mixtae, in which there is a succession in 

 time, but no regular succession in space. These three types appeared 

 successively in geological time : the Simplices were the characteristic Ferns 

 of the primary rocks, though many of that type still survive : the Mixtae 



1 Syst. Filic. Foss., 1836, p. 319. -New Phytologist, vol. v., p. 170. 



3 "Studies," iv., Phil. Trans., Vol. 192 (1899), p. 122. 



2 I 



