2g2 
INTRODUCTION TO 
Polypodium; or else, if we choose to dismember Poly- 
podium, to create an independent and distinct genus for 
each of the independent lines of descent. 
The immediate application of this argument is in the 
limits which I am giving to the family Polvpodiaceae. 
In all recent fern works, Cyatheaceae, Matoniaceae and 
Polypodiaceae are treated as distinct families. To the 
naturalness of this treatment, Dicksonia, with the habit 
and sporangia of Cyathea, but with the undoubted affinity 
of Dicksonia to Dennstaedtia , has afforded a serious 
stumbling-block, which has been passed over or around 
by different writers by assigning different and varying 
limits to Dicksonia, and treating it as more or less distinct 
from the Cyatheaceae. Recent studies, chiefly in England, 
have shown an unquestionable, even if not very close, 
relation, between Cyathea and such Polypodiaceae as 
Peranema and Diacalpe. I am personally satisfied that 
Monachosonmi belongs in the same general group, and 
that the more primitive species of Dryopteris are not 
very remotely related to it. It has long been understood 
by many pteridologists, that primitive Athyrium is hardly 
distinguishable from Dryopteris . The line between 
Cyathea and the Polypodiaceae has, therefore, been 
breaking down. 
Other study in England has convinced me that 
Matonia, or the ancient group of which it is a survivor, 
represents the ancestry of a number of other genera 
recognized as Polypodiaceous such as Dipteris, Cheiro- 
pleuria and Platycerium. 
Independent of Cyathea and its relatives, and of the 
Matoniaceae and their descendants, we have in the 
Polypodiaceae several clear-cut series of descendants of 
Dennstaedtia , or of ancient ferns now best represented by 
Dennstaedtia. These series cross the old tribal lines of 
the Polypodiaceae, sometimes with but little regard for 
