Bower. — Studies in the Phytogeny of the Filicales. 367 
The wing of the pinna, on leaving the midrib, is composed of five cell-layers. 
In passing towards the margin it may be seen to dilate, sometimes by 
increase in number of layers, at other points by simple enlargement of its 
cells. These dilatations are not constant in position, and an examination 
of numerous transverse sections shows that they may vary in position and 
extent in the individual pinna. In the case shown in PL XXII, Fig. 1, c } 
there are two dilatations, the one nearer the midrib than the insertion of the 
sporangia being due to the increase in number of Layers, the other nearer to 
the margin than the sorus being due to dilatation of the individual cells. It 
is important to note these dilatations and the way in which they are produced, 
and their irregularity, as they are similar in nature to features which appear 
in Blechnum. In both cases they may produce swellings on the convex 
surface of the pinna, at or near to the point of its greatest curvature. The 
margin has developed in accordance with the segmentation already seen in 
(PI. XXII, Fig. i, b). It consists usually of three layers of cells, as against 
five or six of the rest of the wing. 
There can be no doubt from its mode of origin, as well as from its 
structure, that here the indusium-like flap is nothing more than the result 
of outgrowth and thinning of the margin of the pinna, which has thus 
become specialized for protective purposes. It may be a question whether 
or not this similarity to Blechnum is an index of phyletic relation, or only 
a parallel development, and the same question may arise also as regards the 
Pterideae. As bearing on this it may be noted that the vascular condition 
of the axis and of the leaf-trace in Plagiogyria is of a more primitive type 
than that of Blechnum , while the origin of the vascular supply to the roots 
lies laterally from the point of origin of the leaf-trace, not directly opposite 
it, as is so very constant a feature in the-Blechnoid series. These divergent 
features indicate some degree of aloofness of Plagiogyria from Blechnum , 
and the more primitive position of the former, which the sporangial 
characters bear out ; as also does the absence of flattened scales from the 
surfaces of axis and leaf. Nevertheless there is an underlying similarity 
that justifies the comparison with Blechnum recognized by the early 
Pteridologists, and so constantly maintained by them. 
Matteuccia intermedia , C. Chr. 
It has been pointed out above how, from the time of Willdenow and 
other early writers, a relation had been recognized between Onoclea and 
Struthiopteris on the one hand and Blechnum on the other. There is 
a general similarity of habit, both types including upright and creeping 
forms with relatively simple pinnation. Sorally, the obvious objection would 
seem to be in the presence of a ‘ true ’ indusium in the former, and its 
absence in the latter. But apart from this, both show dimorphism of their 
leaves, while the sori are essentially superficial, borne on the branching 
