94 



A TEXT-BOOK OF BOTANY. 



(3) There is also a group of ferns known as WATER FERNS 

 which are aquatic in habit ; that is, they live in marshy places or 

 float on water. As representatives of this group may be men- 

 tioned Marsila, from whose slender rhizome that is buried in the 



FlG. 57. Some fern spores. A, B, C, different views of the bilateral spores of the 

 common polypody (Polypodium vulgare), showing outer wall (ep), middle wall (ex), inner 

 wall (end) and line of dehiscence (dl); D, a tetrahedral spore of the royal fern (Osrnunda 

 regalis); E, F, spores of Ceratopteris thalictroides seen in two views. A-D, after Sa.debeck; 

 E-F, after Kny. 



muddy bottom of streams arise the clover-like leaves that 

 float on the \vater (Fig. 59) ; and Salvinia (Fig. 58), which is a 

 small floating plant that develops two kinds of leaves, one which 

 float on the surface of the water and are more or less oblong, and 



FIG. 58. A water fern (Salvinia natans). A, a plant seen from side and showing 

 floating leaves at top attached to the horizontal stem, root-like finely divided leaves beneath, 

 and a cluster of globose sporocarps; B, a view from above showing especially the character 

 of the upper leaves; C, young plant developing from a megaspore (msp). A and B, after 

 Bischoff; C, after Pringsheim. 



another which are filiform, branching, root-like, and submerged. 

 The water ferns are further distinguished by the production of 

 megaspores and microspores. 



(4) The ADDER'S TONGUE FAMILY, to which Ophioglossum 



