16 . 
THE LIMESTONE POLYPODY. 
Polypodium caleareum. 
Plate 7, Fig. 5, Page 253. 
The Limestone Polypody is much hardier and more robust 
than Dryopteris. Its botanical name of Caleareum is exactly 
adapted to the character of this Fern, which loves to grow 
in moist crevices amidst limestone rocks, or on soils in 
limestone districts. It does not seek the same deep shade as 
Dryoptt ris, and its fronds, from their less delicate texture 
and colouring, can better withstand the effects of sunshine 
than the golden green fronds of the ‘Oak Fern;’ yet the 
shadier the nook on earth-bank or rockery, the more finely 
developed will be the fronds of Caleareum, and the deeper 
will be their tinge of green. 
Description. — There is some resemblance between Cal- 
carevm and Dryopteris, in so far only, however, as the 
general shape of the frond is concerned ; but there are 
several unmistakable points of difference. In the first place, 
Caleareum is a larger plant, growing from eight or nine 
inches in height to a maximum of eighteen inches and more. 
The stipes of the frond — though like that of Dryopteris, 
usually longer than the leafy portion — is stouter on account 
of the more vigorous development of the plant. The colour 
of the frond, which is triangular in shape, is not a 
golden green, but a kind of bluish green, having an appear- 
ance sometimes as of a bluish powder scattered over green 
