Peteridophytes 



149 



There are also a few hypnums found intermixed with 

 sphagnum on the surface of bogs, and as everyone 

 knows there are hosts of mosses in all moist places in 

 woods and by watersides. 



Fig. 61. Two floating leaves of the "water shamrock," Marsilea, in the midst 

 of a surface layer of duck-meat (Spirodela polyrhiza). 



Pteridophytes — ^Aquatic f emworts are few and of very 

 unusual types. There are at least two of them, how- 

 ever, that are locally dominant in our flora. Marsilea, 

 the so-called water shamrock or water fern, abounds on 



