THE POLYPODIES. 197 



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 



