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 hve 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 



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

 common polypody {Poly podium vulgare), showing outer wall (ep), middle wall (ex), inner 

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

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

 E-F, after Kny. 



muddy bottom of streams arise the clover-like leaves that 

 float on the water (Fig. 59) ; and Sahinia (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 



-n 



k ^ 



\<a1^' 



f<ik'i^^^'((A\ 



I \ H' 



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 



