366 Bower . — Studies in the Phytogeny of the Fili cates. 
Blechnineae among themselves, for they are probably more nearly related 
to relatively primitive types than are the Asplenieae. 
There remains lastly to be mentioned in this connexion the genus 
Plagiogyria, which formed the subject of the first of the memoirs of this 
series (Ann. of Bot., xxiv, p. 423, April, 1910). Though separated by 
Mettenius as a distinct genus, the species included under that name were 
merged by Sir William Hooker in Lomaria , to which genus they had 
originally been assigned by Kunze. For reasons detailed in my paper 
quoted above, they are shown to constitute a substantive genus, which is 
relatively primitive in its characters, and may be held to be a ‘ synthetic ’ 
type. It shows relations downwards by various characters with the 
Simplices, but the question here will be rather its relations upwards. The 
similarity to certain Pterideae is striking, though the nearness of actual 
relation may be doubtful. But obviously, as the systematic history shows, 
the relation to ( Lomaria ) Blechnum seems to be a closer one, and it is 
apparent chiefly in the dimorphism of the leaves, and the position and mode 
of protection of the sori. 
Plagiogyria. 
Recognizing that there is probably some true relation between Plagio- 
gyria and Blechnum , it is necessary to be clear on the origin and nature of 
the marginal flap which covers the young sori, thus providing a habit- 
character upon which the comparison of these Ferns was originally based. 
Its general appearance was represented in my paper on Plagiogyria (Ann. 
of Bot., vol. xxiv, p. 423, Figs. 1, 2, 14, 15), but certain developmental 
details were there omitted. Transverse sections of the very young fertile 
pinnae of Pl. semicordata show that the lateral flap of the pinna is referable in 
origin wholly to a regular marginal segmentation (PI. XXII, Fig. 1 ,a). There 
is a single oval vascular strand initiated in the midrib of the pinna. As the 
pinna develops, single superficial cells grow out into the characteristic 
glandular hairs, whose terminal cells resemble closely those studied in 
detail by Gardiner and Ito in Blechnum (Ann. of Bot., vol. i, p. 27). As 
development proceeds, the margin of the pinna enters upon less regular 
segmentations, with a large increase in the number of anticlinal divisions 
(PI. XXII, Fig. 1, b). This is in preparation for its rapid extension, and the 
thinning out of its margin as a membranous protection, while the curvature 
is such that it folds over and protects the lower surface of the pinna. Here 
certain large and plasmatically rich superficial cells show great activity of 
growth, and provide after segmentation the mother-cells of the sporangia. 
Sections of a pinna as it approaches maturity show the final result in 
Plagiogyria (PI. XXII, Fig. i,c). The midrib is traversed by a single collateral 
vascular strand of oval form, sharply delimited by a brown-coloured endo- 
dermis. The adjoining tissue of the midrib is mechanically strengthened. 
