12 HOW TO KNOW THE FERNS 



barren ones by the production of a special branch 

 which bears the fructification. The sporangia 

 are large. 



The next order of the Vascular Cryptogams 

 is of comparatively small importance as far as 

 the present study is concerned. It is known as 

 the Rhizocarpece (Pepperworts). The order is 

 divided into two families as follows : 



1. Salviniacea. The only two genera are 

 Salvinia and Azolla ; the latter has been 

 already mentioned. 



2. Marsiliacece. The British example is the 

 Pillwort (Pilularia globulifera). 



The Club Mosses have been divided into six 

 families. Two of these the Lepidodendracece 

 and the Sigillariacece are only represented by 

 fossils ; and one, Psilotacece, has no British 

 representatives. The remaining families all 

 include one or more species which are indigenous 

 to our islands. 



1. Lycopodiacece. These are the Club Mosses 

 proper. Several species of the genus Lyco- 

 podium are British. The Common Club Moss 

 (Lycopodium clavatum) is often abundant on high 

 moors. 



2. Selaginellacea. A large family containing 

 three or four hundred species, only one of which, 

 however, is British ; this is Selaginella spinosa. 



3. Isoetacece. A family of aquatic Club 

 Mosses. The British species is Isoetes lacustris, 

 a plant which is sometimes common in the 

 northern lakes. 



With this brief survey of the Vascular Crypto- 

 gams one may naturally pass to a somewhat 

 more detailed consideration of the life histories 

 of these interesting plants than it has been 

 possible to give in an opening chapter. 



