THE POLYPODIES. 
199 
and in Wales. But from Scotland and Ireland 
it is almost entirely absent. It is, however, not 
an uncommon fern in the limestone districts where 
it grows. 
It is very much hardier in its constitution than 
the Oak Fern, and will sometimes thrive well 
when placed on the sunny or exposed part of a 
rockery, or in the most sunny part of a greenhouse. 
The soil which suits the other Polypodies will suit 
P olvpodium calcareum. But from its fondness for 
limestone it will be supposed that the presence of 
limestone in the soil is desirable. In cultivation, 
therefore, small pieces of limestone should be 
mixed with the soil in which it is grown. Like 
all the Polypodies it has a creeping rhizome, which 
travels half under the surface of the ground, its 
matted fibrous roots finding their way into the 
lower depths of the soil in which it grows, whilst 
from its upper surface grow the clusters of dark 
bluish-green fronds. 
