THE POLYPODIES. 
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4. THE LIMESTONE POLYPODY. 
Polypodium calcareum. 
Taller, darker in hue, and hardier than its rela- 
tive the Oak Fern, is the Limestone Polypody. 
From a height of six inches to a foot, and some- 
times more, it grows, generally preferring a lime- 
stone soil ; hence its name. The frond differs 
from that of the Oak Fern in not having the 
same arrangement of three distinct branches. Its 
colour, too, is very distinct, being a dark green, 
having, as we venture to think, a decidedly bluish 
tinge. The stem is usually about the same 
length as the leafy portion of the frond. The 
shape of the latter is triangular. The pair of 
branches at its base are considerably larger than 
the pair above it. The four branches are attached 
to the rachis, each by a short stem. But the 
branches — or rather they should be termed in this 
case the leaflets — above the two lowest pairs on 
the frond are closely attached to the rachis 
without the intervention of any stalk, and they 
gradually diminish in length, and finally blend 
