20C POLYPODIUM CACCAREUM. 
POLYPO'DIUM CALCA'REUM. 
THIS, by modern botanists, was confounded with P. 
dryopteris ; but, though much resembling, there is no 
reasonable doubt of their being two distinct species. 
Root dark brown, but stouter and less widely creeping 
tban that of P. dryopteris. Its rootlets are almost black, 
scattered, and wiry. The stem of each frond is firm and 
stiff, varying in height from six to eighteen inches, and 
nearly two-thirds of its length being without leaflets. 
The stalks of the two lower leaflets are so much more 
stout tban the stalks of those above them, that some 
botanists consider them as two branches, and call it a 
three-branched Fern. The unleafleted portion of the 
stem is stout, pale, very scaly, and bearing numerous 
small, stalked glands. These glands are found also on 
the leaflets, and give the whole plant a mealy aspect. 
The general outline of the frond is nearly equilateral 
triangular. Leaflets opposite ; the lower ones, in very 
luxuriant specimens, have leafits alternate and deeply 
cut (pinnatifid). The upper leaflets are only deeply cut, 
or lobed ; but the edges of both leafits and lobes are 
scolloped and fringed with very small, stalked glands. 
Each leafit and lobe has a wavy mid-vein, from which 
proceed very regularly, in pairs, lateral or side-veins; 
these side-veins are also very regularly forked, and on 
the upper branch of each fork, about midway between 
the edge of the leafit or lobe and its mid-vein, is a 
circular mass of fructification. The masses become 
