XLii] ATHYRIUM 145 



that Mettenius was writing in pre-Darwinian days. It does not now in any 

 way detract from the interest that Athyriuni possesses in pointing a probable 

 genetic relation with Aspidium, or more nearly with Dryopteris. Seen in the 

 light of more recent examination of soral structure, the extension of a special 

 vascular supply into the receptacle is a feature of some importance for 

 comparison: for all along the line from the Gleicheniaceae through the 

 Cyatheaceae to the Dryopterideae a special vascular supply passes into the 

 receptacle, and it is specially marked in the long stalk of the sorus of 

 Peranevia. Accordingly the presence of a special receptacular strand in 

 Athyrium, which is absent in Asplenimn, marks its nearer relation to 

 Dryopteris and to Perauciiia. 



Fig. 674. Atliyriuin dcciirtatiim (Ktze.) Presl. Part cif a pinna with pinnules 

 bearing sori. Those at the base of each pinnule are sometimes Dryopteroid, 

 sometimes they show variability leading to the Asplenioid type of the distal sori. 



The basal sorus of each pinnule frequently has, like Dryopteris, a kidney- 

 shaped indusium. This is seen in Athyrium filix-foemina {\^^ Roth: but the 

 sori borne distally on the pinnules have the one-sided Asplenioid form, with 

 the fimbriated indusium opening towards the mid-rib. They represent the 

 anadromic side of the horse-shoes. A species that has been specially quoted 

 by Mettenius, as bearing basal sori of the Dryopteroid type, is A. decjirtatuiii 

 (Ktze.) Presl. This was examined in a specimen in the British Museum 

 collected by B. Balansa, Paraguay, 1874: the variability was found as 

 described (Fig. 674). These examples will suffice to illustrate what may be 

 regarded as the conservatism of the basal sori. Here and there they may 

 also be of the Diplazioid type, as Luerssen has noted {Rab. Krypt. Fl. ill, 

 p. 131). Such facts appear strongly to support the Dryopteroid affinity of 

 the Asplenioid Ferns, and to indicate Athyri/un as the nearest point of 

 contact. That contact appears to be with those simpler types of the Dryo- 

 pteroids, which share with Athyrium the open venation and the highly cut 

 leaf-blade. 



As in the Aspidieae so also here the indusium is sometimes liable to 

 partial or complete abortion. This is seen in Athyrium alpestre (Hoppe) 

 Rylands, where the indusium is rudimentary even' in the young state, 

 consisting of hair-like rows of cells (Fig. 673, F, G, H). In the mature state 



Bill 10 



