FILMY FERNS 



153 



The Ferns may be divided into eight families, as 

 follows : 



1. Hymenophyllacece. — These are the Bristle or Filmy 

 Ferns, of which about 200 species have been distin- 

 guished. They are as a rule extremely delicate, and 

 grow only in the presence of abundant moisture. The 

 blades of the fronds as a rule are only one cell thick, 

 but there are a few exceptions. This thinness of the 



Fig. 49. — ^Malb Fben. Poktion of Epidermis moM Undeb-Scrfacb 

 OF A Leaf, x 105. 



st, Stoma; n, nucleus of cell. 



leaves renders them pellucid, and gives them a filmy 

 appearance. Stomata are not present, except in the 

 New Zealand genus Loxsoma. The great majority of 

 the species are tropical; some of them occur as epiphytes 

 ■ — i.e., they grow upon other plants. Two species are 

 found in Britain — the Filmy Fern, Hymenophilum tun- 

 bridgense; and H. peltatum (Desv.). The former is of 

 frequent occurrence in moist, rocky, and shady situa- 



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