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,! 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 Zodea, 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.? 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 proband 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: 
the Stmplices, 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 Afzxfae, in which there is a succession in 
time, but no regular succession in space. These three types appeared 
successively in geological time: the Simpdlices were the characteristic Ferns 
of the primary rocks, though many of that type still survive: the A/ixtae 
1 Syst. Filic. Foss., 1836, p. 319. 2New Phytologist, vol. v., p. 170. 
3 Studies,” iv., Phzl. Zrans., Vol. 192 (1899), p. 122. 
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