fas) 
group as a whole. Their structure clearly indicates that they were 
inhabitants of bogs and wet places. 
6. Ferns and Seed Ferns 
The ferns and seed-ferns are shown together, not because they 
are closely related but because they are similar in superficial ap- 
pearance and have been confused until recent years. Lveryone at 
all familiar with museum exhibitions, or with the roofing shales of 
coal mines, knows that the most abundant fossils are beautiful 
impressions of large fern-like fronds, and until recently the Car- 
honiferous was looked upon as the age of ferns. The discovery 
that many of the more common fern-like plants (Sphenopteris, 
Neuroptcris, Alethopteris, etc.), instead of being ferns, produced 
large complex seeds was one of the outstanding paleobotanical dis- 
coveries of the early years of the present century. Thus a large 
number of supposed Paleozoic ferns have been replaced by seed- 
ferns (Pteridosperms, or Pteridospermophyta). 
Although the true ferns in the older rocks have become much 
shrunken in numbers they are by no means absent, but the simi- 
larity in fohage between ferns and seed-ferns is so great that, 
without the complete evidence of petrified material, it is scarcely 
possible to decide the true status of many genera. Thus 4rchacop- 
teris, shown in the lower left hand corner, is of uncertain affinity. 
paar 
It is based entirely upon the world wide occurrence of impressions 
of large fronds, and thus is in striking contrast with the small 
leaves of all the groups that have been mentioned thus far. It 
appears in the upper Devonian and continues into the lower Car- 
boniferous, showing considerable variation in the details of its 
organization. Its leaves (fronds) were large, occasionally a meter 
in length, bipinnate, with stipules at the base of the leafstalk. 
Sterile pinnules were cuneate or obovate, with entire or variously 
toothed or laciniate margins and dichotomously flabellate veins. 
The fertile (spore-bearing) pinnules, borne on the same fronds 
with the sterile pinnules, had their blades greatly reduced and car- 
ried sessile or short-stalked, large, oval sporangia in groups of twos 
or threes. The sporangia are usually regarded as having no thick- 
ened ring (annus), and consequently Archaeopteris was formerly 
considered to have been a true fern of the tropical fern Order, 
