THE FILMY FERNS. 287 



2. THE ONE-SIDED FILMY FERN. 



Hymenophyllum unilateral. 



THE two Filmy Ferns resemble each other closely 

 in many important respects. But Unilateral, 

 or Wilsoni, as it is also called, is chiefly dis- 

 tinguished from Tunbridgense by having the leafy 

 filaments on the primary branches of the fronds 

 produced on the upper surface only of the branches, 

 instead of on both sides, above and beneath, which 

 is the case in the Tunbridge Filmy Fern. In 

 Unilateral, as in Tunbridgense, what corresponds 

 in ordinary ferns to the leaflets of the fronds are 

 branched veins, with filmy, semi-transparent, wing- 

 like borders. The distinction between the two 

 ferns is somewhat slight. But both are found 

 growing under the same conditions, often in com- 

 pany, their thin wire-like rhizomes densely inter- 

 lacing with each other, and with the roots of the 

 mosses which cover the moist rocky surfaces of the 

 habitats of the Hymenophyllums. 



When the natural conditions under which the 

 Filmy Ferns grow can be imitated in the fern 

 garden, then these beautiful little pellucid-leaved 



