Aquatic plaiits. 
Le long-pet oled, 4-foliolate ; rootstock slen- 
der creeping. 24. Marsii.ia. 
Leaves line ir rigid ; stem corm-like ; plants small ; 
sporangia axillary. 25. Isok iks. 
Leaves minute or rudimentary. 
Pkints robust, rush-like ; s':em liollow-jo:nt3d, simple 
or with verticilLite branches. 26. Eqjjisetum. 
Plants small, moss-like, erect, cr trailing. 
Spores uniform. 27. LvcoponiUM. 
Spores of two k'nds. 28, Ski.aginella. 
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