434 BICKNELL: FERNS AND 
species, the Osmundaceae, three species, and the Polypodiaceae, 
eighteen members, including three commonly regarded as strongly 
marked varieties and one hybrid. 
When discussing the introduced plants it was remarked that 
they included some sixty North American species that were not 
indigenous on Nantucket. Some forty of these are common 
plants of the New England mainland and seventeen are of the west 
and north. Not more than two or three immigrant native species 
have come to Nantucket by way of the south, and these seem to 
be little at home and have not spread from their original stations. 
Here is perhaps a hint that plants of southern conformities may 
léss readily adapt themselves on Nantucket than do species from 
the north and west, as if the present climatic conditions of the 
island might not be encouraging to the advance of more southern 
types. Should this indeed be true it would seem to reveal that 
those southern affinities now in such clear aspect in the flora of 
the island are to be referred back to influences not the same as 
those of today. And there would be accordance in this with those 
now well understood evidences of an extensive flora of southern 
derivation belonging to the New England seaboard of Tertiary 
time, a flora lost to our later day with these broad coastal tracts 
that now lie beneath the sea.* Yet not wholly lost. We find 
it still, much of it, we may believe, in the less disturbed flora of 
our more southern coastal plain, and we find its remnants persisting 
as the merest fringe along the withdrawn more northern coast- 
lines of the present day. And isolated on Nantucket it has been 
preserved to us in that assemblage of southward ranging plants, 
now a primary element in the general composition of the flora. 
Thus, understanding the far back origin of this relationship, 
we may the more readily believe that Nantucket’s possession of 
southern plants may be little attributable to influences operative 
at the present day. 
There is other evidence than the general absence of immigrant 
southern plants on the island that would seem to denote conditions 
less favorable to more southern than to more northern plants. 

* See Fernald, loc. cit. Also, The geographic affinities of the vascular floras of 
New England, the Maritime Provinces and Newfoundland. Am. Jour. Bot. 5: 
219-236. pl. 12-14. 1918. 

