POLYPODIUM. 149 



creeping stem, which often forms densely matted tufts. 

 They are quite smooth, and of a bright light green colour, 

 supported by stipes which are usually about twice as long as 

 the leafy part, and are slender, brittle, and dark -coloured. 

 The outline is almost pentagonal, the frond being divided 

 into three branches, each of which is of a triangular form. 

 One peculiarity about this species, which is in a slight degree 

 shared by its near ally, P. calcareum, is the deflexion of the 

 rachis at the point where the lateral branches of the frond 

 take their rise, but this feature is greatly more obvious in 

 P. Dryopteris. The fronds are divided thus : each branch 

 is pinnate at the base, and pinnatifid towards its point ; the 

 pinnae are also pinnate at their base, then pinnatifid, becom- 

 ing acute and nearly entire at the point ; the pinnules and 

 ultimate lobes are oblong and obtuse. The pair of pinnules 

 at the base of each pinna, close to the principal rachis, are 

 placed so that when the pinnae are exactly opposite they 

 stand in the form of a cross ; the two towards the apex of 

 the branch being smaller than the opposite pair, and more 

 nearly parallel with the rachis. 



The pinnules or lobes have a rather tortuous midvein, 

 from which the venules branch out alternately, being, in 

 those of moderate size, simple, with a sorus near their ex- 



