Filicales. 
243 
certain probably primitive characters, but that those characters that 
are especially Botryopteridean are not found in the Gleicheniaceae. 
Presumably therefore the latter arose from Primofilices allied to, 
but less specialized than the Botryopterideae. 
Protostely occurs both in Gleicheniaceae and Hymenophyllaceae 
and the writer believes that it is primitive in both cases. It is only 
the larger Hymenophyllaceae that resemble the Gleicheniaceae, 
and this is what we should expect if the filmy character of the 
fronds indicates reduction. But the simplest Gleicheniaceae 
appear to have diverged further than Trichomanes scandens from 
the exarch protostele which the writer regards as primitive, for 
their xylem is mesarch. Again, though the fronds of the more 
primitive members of both orders are dichotomous, those of the 
Gleicheniaceae are less primitive, inasmuch, as the angle of the 
dichotomy is occupied by a bud. Professor Bower has shown that 
the relative proportion that the two faces into which the oblique 
annulus of the Gleicheniaceae.divides the sporangium bear to one 
another varies considerably within the order and that every 
gradation between the two extremes is met with (7). This would 
make it probable, as Professor Bower claims, that the annulus is 
homologous throughout the annulate Leptosporangiatae (8). This 
probable homology of the annulus and the similar leptosporangiate 
origin of the sporangia suggest a certain, though a very remote 
relationship for the two orders. 
To the Schizaeaceae the Gleicheniaceae seem to bear a closer 
relationship than to the other orders hitherto discussed. The 
protosteles of the more primitive members of each order differ, it 
is true, in the position of the protoxylem; in this the mesarch 
Gleicheniaceae are, on the view advanced here, less primitive. 
But the dichotomy of the frond of Gleichenia, in which genus a bud 
is formed in the angle of the dichotomy, is exactly paralleled in the 
more primitive Schizaeaceae, and such branching of the frond is a 
rare feature. Professor Bower is of opinion that the cell or cells 
enclosed by the sub-apical annulus of the Schizaeaceae correspond 
to the face of the Gleicheniaceous sporangium that is directed 
obliquely away from the sorus. This face of the sporangium may 
in the Schizaeaceae be reduced to a single cell, but the view of 
the homology of the annulus in the two orders is strongly sup¬ 
ported by the variation of the relative size of the two faces of the 
sporangium within the genus Gleichenia. Such a theory is not, of 
course, tenable if we accept Potonie’s view that the Schizaeaceous 
