30 Wall-Rue 
the formation of another rachis, the base of this leaflet, contain- 
ing the part of the vein that enters the leaflet below the first fork- 
ing of that vein, becomes elongate and forms the part of the new 
rachis between its first leaflet and the old rachis. 
The part in general taken by the venation in the leaf-develop- 
ment will be more readily understood by studying Pl. I, Fig. 2. 
Many of the leaflets of the leaves of the older plants are more 
or less incised between the marginal veinlets. This incision, to 
which is due the peculiar toothed appearance seen so often in 
this fern’s leaves, is not to be confused with the incision described 
above, employed in the leaf-development. 
The plants bear sporangia when very young. The bifoliate 
leaf is sometimes fertile. 
A. ruta-muraria has been included in the genus Asplenium 
by nearly all pteridologists. Newman, however, in 1844, sepa- 
rated it from Asplenium, to form, together with A. septentrionale 
and A. germanicum, a genus which he named Amesium. But 
A. septentrionale had already stood as the type of a genus of 
Mirbel’s.* The affinity of A. ruta-muraria with A. septentrionale 
appears very marked, especially on comparing the leaf-devel- 
opment of the two species, and, taking into consideration the 
flabellate venation and other peculiarities which characterize 
these two species, they appear sufficiently distinct to warrant 
restoring Mirbel’s genus Belvisia and including A. ruta-muraria 
in it. 
* Belvisia Mirb. in Lam. & Mirb. Hist. Nat. Veg. 3: 405. 1802. 
