654 GENERAL COMPARISON OF THE FILICALES 
the overlap represents those which are in course of transition, or are 
believed to have recently passed from the one state to the other. With 
these explanations the scheme may be taken as representing the con- 
clusions arrived at in the preceding pages. 
Of the Simplices the Marattiaceae stand somewhat isolated from modern 
Ferns, both anatomically and sorally. They are approached most nearly 
by the Gleicheniaceae in point of the sorus, but in anatomy and in habit 
they stand widely apart from them. Their stock probably never progressed 
beyond its present state. If they had any near relation with other living 
Ferns it must have been very far back. 
The other very ancient family, the Botryopterideae, shows obvious 
relations with the Osmundaceae, both in type of shoot, in anatomy of 
the earlier species, and in sporangial characters. There appears to be 
an anatomical resemblance, on the other hand, to the Hymenophyllaceae, 
which extends to the external characters of the shoot also; but the sorus 
of the Hymenophyllaceae is widely apart, having passed to the basipetal 
type. It is perhaps in relation to their consequent increase in number 
that reduction of size of the sporangium is here shown, and especially 
illustrated in Z7tchomanes. None of these three related families appear to 
have progressed further than their living representatives: they are held 
to be blind branches of descent. 
The Schizaeaceae appear as an isolated family, though nearest to the 
Gleicheniaceae: their solitary marginal sporangia show analogies of structure, 
but not of position, with those of Glerchenia on the one hand and of 
Osmunda on the other: it is, however, probable that their monangial 
sorus is a result of reduction from a radiate type, such as is seen in 
some species of Gleichenia. Anatomically also their simpler types approach 
Gleichenia, but the upright genera, Anezmia and Mohria, appear to have 
progressed along a line eof their own to a dictyostelic structure. The 
Schizaeaceae also appear to have been a blind branch. 
The Gleicheniaceae are somewhat isolated, from the fact that they 
show cross characters: their sori compare most nearly in position and 
structure with those of the Marattiaceae, but their type of shoot and their 
anatomy correspond rather with the Schizaeaceae. Thus among the Ferns 
which show their primitive character by their large spore-output per 
sporangium, including the Simplices and the Hymenophyllaceae, there 
appear to be several fairly distinct lines: it is possible to link these 
together by hypothesis as to a common ancestry, but there is no distinct 
evidence of their common descent from any known Fern-type. This is 
indicated in the scheme by the convergent but disconnected lines, the 
longer lines of the Botryopterideae and Marattiaceae indicating their 
priority in the fossil record. 
From the Simplices, though with uncertainty as to their definite 
reference to any exact origin, at least two other main lines in addition 
to the Hymenophyllaceae appear to have proceeded to the basipetal type 
