222 DR. A. C. SEWARD: 
forms from different geological periods tends to reduce to a minimum the 
idea of time and gives a false impression of rapid change. 
“ Thus ignorant of man and of the ages 
That he calls ancient, ignorant of all 
The sons who follow as their grandsires led, 
Stands Nature ever young— 
Or rather she proceeds, but so long 
A course she seems to stand.” 
I propose to pass in review the following families :—the Gleicheniaceæ, 
the Matonineæ, the Dipteridinæ, the Schizæaceæ, the Marattiaceæ. It must 
be frankly acknowledged that I am travelling over a familiar road ; my 
object is rather to bring together some of the facts already published both by 
other palæobotanists and by myself than to attempt to add much that is new. 
Palæozoic forms are excluded partly because of the difficulty of precise 
statement on their affihity, but chiefly because it is not until the Mesozoic era 
that existing types become clearly defined. Before dealing with these 
families brief reference will be made to the genus Onoelea, a member of the 
Polypodiaceæ which is probably the most modern though by far the richest in 
genera of all fern families. 
Onoclea sensibilis *, the only species of Onoclea recognised by some authors, 
is characterised by dimorphic fronds, the sterile leaves having linear pinnæ 
entire or lobed and with anastomosing veins, the fertile leaves bearing 
pinnate branches almost devoid of laminæ with small infolded lobes 
enclosing sori. This Fern ranges from Florida to Newfoundland and to 
Nebraska in the west ; it occurs also in the far east of Asia. Fossil leaves, 
some of them indistinguishable from those of the recent plant, are recorded 
from Upper Cretaceous rocks in Colorado, Dakota, Montana, and in other parts 
of the United States ; precisely similar specimens occur in Lower Tertiary 
strata in Western Greenland and in the Island of Mull. The recent 
discovery of well-preserved spores by Mr. Edwards of the British Museum 
on some of the Mull material confirms the identification ef the sterile and 
fertile fronds. A well-known paper by Asa Gray first demonstrated the 
resemblance between the existing vegetation of the Eastern region of North 
America and that of Japan, a resemblance which it is generally believed 
extended to Europe in pre-Glacial times. Hooker in his classic paper on 
Arctic floras accepts Darwin’s hypothesis, based on opinions first advanced by 
Edward Forbes, that from cireumpolar land plants migrated to the South 
along divergent lines as the oncoming Glacial period caused a lowering of 
temperature. The work of Mr. and Mrs. Clement Reid on the later 
Tertiary floras of Western Europe has afforded striking testimony of the 
* Photographs of recent and fossil Ferns were shown on the screen in illustration of the 
lecture, 
