SEED-BEARING FERNS 83 
stone cliffs, somewhat sheltered by brush, grew Sphen- 
omeris clavata (L.) Maxon, well named, for the sterile 
pinnae are wedge-shaped and the fertile club-shaped. 
Anemia adiantifolia (L.) Sw. and Asplenium dentatum 
L. grew in like places. 
Polypodium exiguum Hew. and Adiantum melano- 
leucum Willd. grew in shaded places on the limestone 
cliffs. A peculiar fern ally, suggesting Gnetwm in ap- 
pearance, Psilotum nudum (L.) Griseb., braved the sun 
on the open cliffs. 
Seed-bearing Ferns. 
By F. H. Know.ton, 
United States Geological Survey 
The prevailing belief of three centuries ago as regards 
the mysterious process supposed to surround reproduc- 
tion in ferns was well voiced by Shakespeare when he 
says: ‘We have the receipt of fern seed; we walk in- 
visible.” 
Now, since the compound microscope and an improved 
technique has put us in the possession of the intricate 
details of reproduction and development in the ferns, 
it is not much to be wondered that it then seemed so 
shrouded in mystery. But, complicated as the process 
is known to be, it is only a step in the history of the 
evolution of the great group of ferns. 
Until a few years ago we rested secure in the belief 
that the dominant types of living plants—the flowering 
plants—were dominant because they had developed the 
seed-bearing habit. Within the past dozen years, 
however, it has been demonstrated that in the oldest 
land flora of which we have any knowledge, namely, 
that which lived in early and middle Devonian time, 
there was a great group of plants, which, while still 
