THE LIMESTONE POLYPODY. 93 
the base, and with a few scattered deciduous scales upwards 
when young, minutely glandular, pale watery-green, dulled by the 
glandulosity of the surface; lateral to the caudex, adherent, dis- 
tinct. Rachis glandulose, the part forming a stalk to the lower 
pinne much shorter and distinctly smaller than that between the 
first and second pairs of pinne. 
Fronds six to eighteen inches in height, including the stipes, 
which is usually more than half, sometimes two-thirds at least, of the 
length: erect, of a firm herbaceous texture, deep dull grayish-green, 
glandulose, elongately deltoid-pentangular, the pentagonal outline, 
however, less manifest than in P. Dryopteris, in consequence of the 
less comparative length of the stalks of the lower pinn®. The 
fronds are not truly ternate, though the larger size of the lower 
pinne gives them a subternate appearance; they are bipinnate, 
with the lowest pair of pinn; subbipinnate or sometimes bipinnate 
on the posterior side, which is the most developed. 
Pinne variable, opposite below, the lower largest pair sometimes 
each six inches long, obliquely triangular, stalked, often bipinnate ; 
the next pair stalked or sessile, pinnato-pinnatifid ; the upper ones 
all sessile, pinnate or pinnatifid, becoming gradually less divided 
towards the apex. Pinnules of the lower pair larger on the 
posterior side, those of the other pinn® nearly equal; those of each 
succeeding pair resembling the smaller ones of the pair next below 
them. Pinnulets or lobulets oblong, obtuse, entire or crenated. 
Venation of the lower posterior pinnules consisting of a stout costa 
or midvein, with a flexuose vein running up the centre of each 
lobulet; this is alternately branched, the venules extending to the 
margin, simple, or very commonly forked, the venule if simple, and 
the anterior veinlet if divided, bearing a sorus near to the margin. 
Or, the vein extending up the lobulet may be regarded as a midvein ; 
its branches, sometimes simple and soriferous, as veins; and the 
branches of these, of which the anterior is mostly fertile, as venules. 
Fructification on the back of the frond, scattered over its whole 
surface. Sori small, circular, consisting of numerous crowded 
spore-cases, entirely without indusia, arranged in a linear sub- 
marginal series along each side of the lobulets; or about the sinus, 
in a series between the midrib and margin, when the lobules are 

