240 DR. A. C. SEWARD : HOOKER LECTURE, 1922. 
northern floras. If the early Mesozoic Ferns came froin Paleozoic ancestors 
it is much more probable that they were the descendants of plants which 
formed part of the rich northern flora. 
Whatever may have been the main trend of migration, and wherever the 
ancestral homes may have been, such Ferns as Gleichenia, Dipteris, and 
Matonia are impressive examples of constancy in a changing world ; in the 
course of their wanderings from one part of the earth to another they have 
suffered but little change since the days which preceded the mysterious rise 
to ascendancy of the Flowering plants. 
Continental areas repeatedly shifted and land and sea changed places : it 
needs no geological knowledge to grasp the fact that the rocks accessible to 
investigation cannot give us all the clues we seek. Parts of old continents 
remain ; others are beyond our reach. 
“In some green island of the sea, 
Where now the sliadowy coral grows 
In pride and pomp and empery 
The courts of old Atlantis rose." 
Mr. G. M. Trevelyan, contrasting our very imperfect knowledge of 
Shakespeare himself and what we know of his works, says—“ For however 
many thousands of years descendants may last, neither we nor our remotest 
descendants will ever see into the Mermaid Tavern. Its doors are closed, its 
windows shuttered, Time Past has got the key, and our scholars can only 
sweep the doorstep.” There is consolation in the fact that among the 
sweepings there is still treasure to be found. 
EXPLANATION OF THE PLATES. 
PLATE 16. 
Map A. Distribution of Gleicheniacex. 
PLATE 17. 
Map B. Distribution of Ferns of the Dipteris-Matonia alliance. 
PLATE 18. 
Mar C. Distribution of Schizæaceæ. 
PLATE 19. 
Map D. Distribution of Marattiacez. 
