412 Bower. — Studies in the Phytogeny of the Filicales. 
think that here, as in Blechnum and Scolopendrium > the simplest types 
have been condensed from an ancestry where the leaves were more freely 
branched. 
It will be best to start from those simpler and more regular types where 
the sori are disposed obliquely on either side of the midrib and overlap one 
another, their indusial flaps all facing acroscopically. This arrangement is 
characteristic of § Thamnopteris , Presl, and of §§ Eu-Asplenium. There is, 
however, a difference within these subgenera in the inclination and the over- 
lapping of the sori, according to the breadth of the leaf. Where, as in 
A. ( Thamnopteids ) nidus , L., the leaf is very broad and the sori long, they 
often stand out almost at right angles to the midrib, and are crowded so 
that the overlapping is very close. But in those species in which the pinnae 
are narrow and elongated, and especially at the acuminate apices of such 
leaves, the sori may be only very slightly inclined to the midrib, or even 
almost parallel with it, and may overlap one another very little or not at 
all. A middle position is seen in such a species as A. obtusatum , Forst. 
(PL XXXII, Fig. 32). 
Examples of the arrangement of the sori in narrow-leaved species 
are seen in Hooker’s Species Filicum, iii, PI. CXC-CXCV. In A. horri - 
rtum , Klf., and especially at the excurrent apex of the pinna, the position 
of the elongated sori is parallel to the midrib, and with the indusial flap 
directed towards it, just as in W oodwardia. This was particularly well seen 
in New Zealand specimens collected by T. F. Cheeseman, from which the 
drawing has been made (PI. XXXII, Fig. 33). Another good example is 
seen in A. serra , Langsd. & Fisch., collected by Purdie from Santa Martha 
(Fig. 34). If a comparison be made of such cases with Woodwardia , and 
especially with such a case as that shown by Mettenius for W. virginica 
(Fil. Hort. Lips., Taf. VI, Fig. 2), the similarity is unmistakable, while the 
oblique position and the overlapping of the sori are more pronounced in the 
latter than they are in the species of Asplenium quoted. 
But there remain to be considered those more complicated dispositions 
of the sori found in the section § Diplazium , Swartz. Here two sori are fre- 
quently placed back to back upon a single vein. A rather complicated and 
irregular example of this is shown in PI. XXXII, Fig. 35, in the case of A. 
(Dipl.) celtidifolium , Kze.,from material collected in Jamaica. The underlying 
principle of arrangement of the sori is foreshadowed by B. punctulatum , var. 
Krebsii (Fig. 28, c , d). Here accessory soral tracts are seen in the spaces 
between the branches of a main vein (marked x in figures), which spaces 
are usually without sori in Scolopendrium and have, for grounds explained 
above, been held to correspond to a suppressed pinnation. The presence of 
these sori may here be held to be a consequence of a less perfect suppression 
of an extra pinnation than that seen in Scolopendrium itself. These extra 
sori were noted and lettered (b) in Mettenius’s Fil. Hort. Lips., PI. V, Fig. 7. 
