28 Wall-Rue 
Venation flabellate, free or with occasional areola: veins 
repeatedly forked. 
Sori short-oblong to linear, borne on veins near and opening 
toward centres of ultimate segments of leaf: indusia whitish, 
delicately membranous, ciliate-erose. 
Spores ovoid-bean-shaped, minutely roughened. 
Habitat. Seams, pockets, and ledges of calcareous rock: 
usually exposed to the sun or in partial shade. Growing in tufts. 
Range. Vermont, southern Ontario, and Michigan, south to 
Alabama and Missouri. 
Asplenium ruta-muraria. Linneus, Species Plantarum, 1081. 1753. 
Tue leaf-blade of Belvisia ruta-muraria is at first simple 
and more or less rounded, and somewhat truncate at base or 
soon becoming so (Pl. I, Figs. 1a, 2a, 3a). It then develops 
into a blade consisting of a single leaflet-bearing rachis, in the 
following way. 
A slight incision forms at the apex of the blade (Fig. 2 6), and 
gradually deepens until the blade is cut into two leaflets (Fig. 3 
cdc’d’). One of the two remains, temporarily, undivided (Figs. 
3c’,4c’). The other becomes at base elongate and narrow, form- 
ing the beginning of a rachis, and divides above into two leaflets 
(Figs. 3d’, 4a’, 5 dd’), as the simple leaf-blade divided. The rest 
is repetition: one of every two leaflets formed remaining undi- 
vided, and the other becoming transformed at base into an exten- 
sion of the rachis and dividing above into two leaflets. Which of 
the two leaflets remains undivided depends in each case upon 
which of the two in the preceding case remained undivided: if 
the left leaflet in the one case, the right leaflet remains undivided 
