168 IX. ASPLENIUM. 
numerous, terminal, and adherent to the caudex, deep 
green, from one to six inches in length, growing up in 
May and June, and continuing green through the winter. 
The stipes is smooth and slender, more than half the 
length of the frond, green except at the base, where it is 
blackish-purple. The frond is more or less triangular in 
outline, usually bipinnate, but sometimes in young or 
imperfect specimens, only pinnate. Very young seedling 
plants have the fronds simple and kidney-shaped, and in the 
next stage pinnate, with a single pair of roundish reniforrn 
pinnae. The pinnae of ordinary mature plants as well as 
the pinnules are alternate. The pinnules are rhomboidal, 
roundish ovate, or obovate with the base wedge-shaped, 
sometimes cuueate with the apex truncate; the upper 
margin is always irregularly toothed or notched, the 
wedge-shaped base entire. The ultimate divisions of the 
fronds, whether pinnae or pinnules, are without a dis- 
tinct mid-vein, but a series of veins arise from the base, 
becoming in their progress branched, and spreading out- 
wards, the number of branches or venules usually corres- 
ponding with that of the marginal teeth. On the inner 
side of these venules the sori are produced, several on a 
pinnule ; they are linear-elongate, covered by long nar- 
row membranous indusia, which have their margin ir- 
regularly jagged or sinuated, and are soon obliterated by 
the spore-cases, which become confluent, and usually at 
length cover the entire under surface. The fructification 
is mature in August. 
A very common species, found in the fissures of rocks, 
and more abundantly on old walls, exhibiting a predi- 
lection for brick walls. It is generally distributed over 
Europe, and is said to be not uncommon in some parts 
of North America. This fern was formerly reputed to 
possess pectoral qualities. The cuneate-truncate form 
above mentioned, somewhat resembles A. Germanicum, 
and is sometimes mistaken for it. 
Th Wall Rue grows better in fragments of old brick 
