408 Bower . — Shi dies in the Phytogeny of the Filicales . 
to the state already noted in B. boreale (Fig. 23). The usual point for the 
interruptions of the fusion-sorus to appear is towards the anadromic end of 
the arch. Several intermediate conditions are shown in Fig. 28, e\ in one 
case the vascular commissure is complete but the indusial flap is interrupted ; 
in another, the indusial flap is still continuous but the commissure interrupted, 
with an isolated tracheide lying in the gap. In a third, both flap and com- 
missure are interrupted. In such cases, while the vein-endings run outwards 
towards the margin, a process of storage xylem of the commissure underlies 
the detached ends of the receptacle. More advanced states of interruption 
of the fusion-sorus are seen in Fig. 28, c , d. These show how the detached 
portions may be extended outwards towards the margin of the widening 
pinna, finally taking an arrangement in pairs, with the indusial flaps facing 
one another. 
Two other complications are apt to be introduced which are important 
for comparison with derivative forms, and they are shown in their simplest 
terms in Fig. 28, c, d. The first of these is the formation of secondary 
branches of the veins, which lie in the space between the forks of the 
primary veins. Frequently these run out to the margin of the pinna without 
any sorus attached to them. But this is not always so. At the points 
marked x in Fig. 28, c } d , there are one or two small supernumerary sori 
attached to such branches ; in the more elaborate types, and especially 
towards the base of the pinnae, these appear more regularly. They must 
be held to be new formations, and not directly derivative from the 
disintegration of the fusion-sori, like the rest. It will be seen that the 
former of these innovations becomes a regular feature in Scolopendrium. 
The latter is important for comparison with certain types of Asplenium . 
It is necessary first to put the phenomena thus seen in B. punctulatzim y 
var. Krebsii , into relation with questions of pinnation, as illustrated in 
B. longifolium. It will be noted on comparison of the drawings, and 
especially their basal parts, that the margins of the pinnae of B. Krebsii are 
sinuous, also that indentations of the margin lie peripherally to the pairs 
of sori ; the convexities are obliquely opposite to the spaces between the 
forks of the primary veins, and accordingly they subtend morphologically 
the primary veins themselves. So far, then, as there is any indication of 
a further pinnation, each of the pinnae (as marked by the convexity of the 
margin) is served by one of the primary veins. The correctness of this 
conclusion is indicated by a comparison with the distal end of the pinnae of 
B. Fraseri (PI. XXIX, Fig. 21). There, a pinnule subtends and is traversed 
by each primary vein, though the fusion-sorus does not there show the 
archings and interruptions seen in B. Krebsii . 
In order to maintain the comparison on the one hand with Blechnum 
and on the other with Scolopendrium , the development of the sorus of the 
var. Krebsii has also been traced. The initial steps accord with those of 
