28 Wall-Rue 



Venation flabellate, free or with occasional areolae: 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. Linnaeus, Species Plantarum, 1 08 1. 1753. 



The leaf-blade of Belvisia ruta-muraria is at first simple 

 and more or less rounded, and somewhat truncate at base or 

 soon becoming so (PI. I, Figs, i a, 2 a, 3 a). It then develops 

 into a blade consistmg of a single leaflet-bearing rachis, in the 

 following way. 



A slight incision forms at the apex of the blade (Fig. 2 b), and 

 gradually deepens until the blade is cut into two leaflets (Fig. 3 

 cdc' d'). One of the two remains, temporarily, undivided (Figs. 

 3 c', 4 c'). The other becomes at base elongate and narrow, form- 

 ing the beginning of a rachis, and divides above into two leaflets 

 (Figs. 3 d', 4 a', 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 mto 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 



