Bower . — Studies in the Phytogeny of the Filicales. 41 1 
petal succession may be seen in the early stages, the sorus becomes later 
distinctly ‘ mixed ’ in character. A comparison of these earlier stages of the 
double sorus of Scolopendrium with those of var. Krebsii leaves no doubt 
that the two are very closely allied. 
Transverse sections of the stem of S. vidgare show that the vascular 
arrangement is essentially that of the Blechnoid type, with a dictyostele 
(Text-fig. 18). The root-steles come off in the same way from the middle 
of the meristeles of the axis just below the leaf-gaps, but each may divide in 
its course through the cortex, so as to supply several roots instead of only 
one. Above the point of departure of the root-stele, the foliar gap opens 
and gives off from each margin a strap-shaped vascular strand ; the pair of 
these constitutes the leaf-trace. These arrangements coincide with those of 
the simple Blechnoid Ferns. Proceeding up the leaf-stalk, the pair of leaf- 
trace strands may fuse together to form the com- 
plex X-shaped structure known as characteristic 
of this genus and of Asplenium (Russow, Vergl. 
Unters., p. 100, Taf. X, Fig. 16 ; Luerssen, Rab. 
Krypt.-Flora, iii, p. 120). Lastly, the young parts 
are densely covered by ramenta, which bear at 
their apex a large mucilage gland, similar in 
character to the well-known mucilage glands of 
Blechnum . All of these characters together 
strongly support the near relationship of Scolo- 
pendrium to Blechnum , and especially to some of 
the less specialized types of that affinity; while 
the peculiar soral features are explained through var. Krebsii , as derived 
from the simpler Blechnoid type by its becoming sinuous and ultimately 
disintegrated in relation to increased assimilating area. 
Text-fig. 18. Transverse 
section of the stock of Scolo- 
pendrium vulgare , Sm. x 3. 
Asplenium . 
The relations between Scolopendrium and Asplenium have always been 
recognized as very close, and the varieties of B. punctulatum , and of other 
Blechnoid derivatives, offer strong evidence that this large genus has sprung 
from a Blechnoid source. The genus is, however, so large and so variable 
in form that it is not possible at present to treat it fully. I shall hope to 
return to this on some future occasion. It includes some hundreds of 
species and has been subdivided variously by systematists, some including 
all those species in a single genus, others dividing them among as many as ten 
distinct genera. But whatever the systematic arrangement may be, there is 
general agreement that the whole body of species form a very natural 
group. Some are simple in the outline of the leaf, others run into high 
degrees of branching, and this character has been used by most writers as 
one of the bases of their systematic arrangement. There is some reason to 
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