376 



SOT ANT. 



Bpore cavity (Fig. 361, 0, r). By the contraction of this ring the ripe 

 sporangium is ruptured and the spores set free. In some cases, instead 

 of forming a ring, tlie elastic cells are arranged as a group at one side 

 or end of the sporangium. 



Six families or suborders of the Perns may be distinguished, if we 

 take into consideration the characters derived from the asexual genera- 

 tion. They have Leen arranged as follows :* 



1. Oleicheniacem. — Sporangia sessile, splitting vertically, furnished 

 with a complete horizontal ring. Sori composed of very few sporangia ; 

 receptacle not elevated (Fig. 263). Fronds with very distinct dichot- 

 omous branching. Genera two (Platyzmna smd Qleichenia) ; species 

 thirty, mostly confined to the southern hemisphere. 



2. SymenophyUaeem.—' 

 Sporangia sessile, split- 

 ting vertically, furnish- 

 ed with a complete 

 horizontal ring. Sori 

 composed of numerous 

 sporangia inserted on a 

 long filiform receptacle 

 (Fig. 264). Leaves of 

 filmy texture (usually of 

 a single layer of cells), 

 with pinnate branching. 

 Genera two (Hymeno- 

 phyllwm, and Trichoma^ 

 nes) ; species 150 to 200, 

 mostly confined to the 

 tropics. 



3. Gyatheacem. — Spo- 

 rangia nearly sessile, 

 splitting transversely, 



Fig. 262.— Development of the spores of Aspldivm 

 Filix-^mas. I., & mothnr-cell containing aniicleus^; 

 //., the same after the absorption or the nucleus ; 

 ///., the mother-cell, with two large clear nuclei — 

 eometimea a line of siparation is evident, as in the 

 figure ; /F., the mother-cell, with four clear nuclei, 

 wTiich appear after the absorption of the two in 

 ///. ,* V.J the four daughter-cells tj'oung spores) 

 which form from IV.; VI., VII., VIII., different 

 relative positions of the developing spores ; IX., the 

 perfect spore, x 550. — After Sachs. 



* The characters and arrangemont of the suborders of ferns are 

 taken from the article " Ferns," by W. T. T. Dyer and J. G. Baker, in 

 the " Encyclopaedia Britannica," ninth edition, Vol. IX., p. 104. For a 

 systematic account of the Ferns the student is referred to " Synopsis 

 Filicum : a Synopsis of all Known Ferns," by W. J. Hooker and J. G. 

 Baker, London, 1873 The student may profitably consult the lollowing 

 recently published American works, viz ," The Ferns of North America," 

 oy D. C. Eaton, the plates by J. H. Bmerton, now being issued in parts ; 

 "'Ferns of Kentucky " by John Williamson, 1878 ; " Ferns in Their 

 itibmes and Ours," by John Robinson, 1878 ; and " Ferns of the South- 

 west," by D. C. Eaton, in Lieut. Wheeler's " Report upon U. S. Geo- 

 graphical Surveys West of the One Hundredth Meridian," Vol. VI, 

 1878 ; Underwood's "Our Native Ferns," ]'881. 



