Bower . — Studies in the Phytogeny of the Filicales . 371 
It was necessary to make these points of terminology clear at the outset 
for purposes of lucid description. But the comparative discussion of the 
facts now to be detailed will be deferred to a later page. The description 
of the numerous species on which observations have been made will be so 
arranged that those species in which the structure of the fertile pinnae is the 
simplest, and which accordingly conform most nearly to the type seen in 
Plagiogyria or in Matteuccia intermedia , will be taken first, and from these 
the description will proceed to those which show a higher complexity. 
i. The Sorus of Blechnum and its Relation to the ‘Flange'. 
(A) Blechnum discolor (Forst), Keys. 
This is a large upright species which may become subdendroid in habit. 
Runners may arise from the base of the plant, which, like the main axis, 
show a dictyostelic structure essentially similar to that seen in B. tabulare 
(see below). The leaf-trace comes off from the sides of the foliar gap in 
the form of two equal strands, which are distinct in origin from the first, 
as in Matteuccia. Higher up in the petiole of the fertile leaf, branching 
of the strands may occur, and the system settles down as a group of three, 
the lateral strands showing the usual adaxial hooks. The fertile pinna is 
similar in position and character to that of Plagiogyria , and like it is supplied 
by a single strand in the midrib (PI. XXII, Fig. 3, /, g, h). From this 
lateral strands arise supplying the lateral expansions, and these are them- 
selves curved strongly downwards as in Plagiogyria and Matteuccia , so as 
to protect the sori borne upon the lower surface. The lateral expansions 
show considerable irregularity of outline as seen in the transverse section ; 
in this they resemble what has been seen in Plagiogyria , though here the 
irregularity is more marked. It is seen in Fig. 3,g,k. Passing outwards 
laterally from the midrib, the thickness of the flap is seven or eight layers 
of cells. It then widens out to a considerably increased thickness at the 
point of greatest curvature, narrowing again where the sorus is inserted, and 
finally thinning out to a single layer where the margin is membranous or 
‘ indusioid \ The effect of this on the external appearance of the whole 
pinna is to give it roughly a four-angled form, with one of the flat sides 
facing upwards, and marked by longitudinal ridges, which, as they project 
alternately more and less strongly, form rows of rounded bosses. This is 
a form which is pretty general for the fertile pinnae of the section Lomaria , 
to which the simpler species belong. 
The sori appear as linear masses of sporangia, seated laterally in the 
concavity of the lower surface, and are usually continuous. The receptacle 
is supplied by veins which run out obliquely from the midrib of the pinna. 
As they reach the receptacle, each widens out laterally in a fan-like manner, 
so as to meet the next, and thus a continuous vascular 4 commissure * is 
