146 HISTORY OP BRITISH FERNS. 



four distinct kinds, with some variations of the common 

 sort; some of these have the fronds persistent, and so 

 become evergreen, while in others they last but from spring 

 to autumn. 



The Polypodies derive their name Polypodinm, which 

 literally means, many-footed, from the branching of their 

 creeping stems, the tubercular protuberances on which, in 

 the earlier stages of development, have some supposed re- 

 semblance to those on the feelers of Polypes. 



POLYPODIUM CALCAREUM, Smith. The Limestone Poly- 

 pody. (Plate III. fig. 1.) 



This Pern is known from P. Dryopteris to which it is 

 so nearly related that some botanists do not consider it dis- 

 tinct by having its fronds less decidedly, though somewhat 

 three-branched, and by having its surface covered with small 

 stalked glands, which give a mealy appearance to every part 

 of the fronds. To us these two plants appear quite dis- 

 tinct, for, in addition to the points of difference already re- 

 ferred to, the fronds of this are of a dull deep green, more 

 rigid, and without the marked deflexure of the rachis so 

 obvious in its ally ; and the young fronds, instead of being 

 rolled up in three little balls, have their pinnae all rolled up 

 separately. The glandular surface of the whole frond is 



