CH. XLi] ASPIDIEAE 121 



B. Intertnediate: the petiole receives 2-3 strands, two stronger are adaxial, but fissions 

 upwards give finally 4-6 strands. 



Polystichtnn lonchitis (L.) Roth. Holly Fern. 

 Polystichum aadeattan (L.) Schott. Prickly Shield Fern. 



C. Relatively coinplex : the petiole receives 5-1 1 strands, the two adaxial being larger. 



Dtyopteris filix-mas (L.) Schott. Male Shield Fern. 

 Dryopteris sphiulosa (Mull.) O. Ktze. Prickly Shield Fern. 

 Such data have been elaborately tabulated by Luerssen for the German Ferns of this 

 affinity, as a help to diagnosis of the species. It may, however, be a question how far this 

 can be reliable, since all Ferns pass in their ontogeny onwards from the simple protostele 

 and undivided leaf-trace, and so the anatomical diagnosis can only apply to the adult state. 

 What does appear from such results is, that all may be regarded as elaborations of structure 

 based upon the simplest type. A: and that the circumstances which have been operative 

 in producing the results observed are the habit— creeping and lax or upright and compact 

 — and the actual size of the part examined. 



Of the genera which are associated by Diels in this very comprehensive 

 group, a number bearing kidney-shaped indusia are clearly related to 

 Dryopteris {Nephrodinin). This remark applies particularly to such genera 

 as Luerssenia Kuhn, Fadyenia Hook., Mesochlaena R. Br., and Didymochlaena 

 Desv. (Vol. I, Fig. 236, G, M). Others have a fully circular form of indusium, 

 as in Aspidium and PolysticJiiiin (Fig. 236, i\^: others again, owing to absence 

 of an indusium, have been ranked as Polypodium, for instance the native 

 Beech Fern (styled P. Phegopteris L.), and the Oak Fern (styled P. Dryo- 

 pteris L.), both now included in the genus Dryopteris. Others again are held 

 to be of this same affinity, though their sporophylls appear to be Acrostichoid, 

 with the sori spreading over the originally vacant leaf-surface. As a sub- 

 stantive genus of this nature, but recognised as of Dryopteroid affinity is 

 the widely spread Polybotrya Humb. & Bonpl. It thus appears that the 

 sorus of those Ferns which are held as Dryopteroid is variable in its character, 

 but comparison indicates that they may all be traced in origin to a central 

 type, with superficial sori, such as that represented in essential features by 

 Dryopteris filix-mas. 



There are, however, other Ferns which have been grouped by Diels with 

 the Aspidieae, with which the relationship may be held as open to doubt : 

 the most notable of these is Dipteris. This genus has been already assigned 

 a distinct position of its own in Vol. Ii, Chapter XXXIV, on the basis of its 

 palaeontological history, which traces the Dipterids back as such to Mesozoic 

 times. They constitute a distinct phylum of their own, with which should 

 probably be ranked also Neocheiropteris; this genus also will accordingly be 

 removed from the position among the Aspidieae assigned to it by Diels. 

 There is again considerable doubt as to the propriety of placing Deparia 

 among the Aspidieae: this question will be taken up later. The remaining 



