26 FERNS IN THEIR HOMES AND OURS. 



or termination of a vein, &c. These genera are 

 again united into orders, based upon the form of 

 the spore-case and the position of the ring of cells 

 which is found upon most sporangia. Hooker 

 (" Synopsis Filicum"), the authority most frequent- 

 ly quoted, has five orders, or sub-orders, as, accord- 

 ing to his mode of dividing, they become. Aside 

 from the Opkioglossums, they run thus : 



(Ring horizontal) I. Gleicheniaceae (2 gen., 24 sp.) 



(Ring vertical) II. Polypodiacese (13 tribes) (59 gen., 2,098 sp.) 



(Ring at one side) III. Osmundaceae (2 gen., 10 sp.) 



(Ring apical) IV. Schizaeaceae (5 gen., 60 sp.) 



(No ring) V. Marattiaceae (4 gen., 20 sp.) 



This very unequal division gives the Polypodiacece 

 five-sixths of all the genera and twenty-six twenty- 

 sevenths of all the species. Hooker and Baker 

 also divide the genera into tribes, and in the large 

 genera distribute the species among sections or 

 sub-genera. 



Smith, in the " Historia Filicum," divides the 

 ferns thus : I. Eremobrya, those ferns whose fronds 

 are articulated along a creeping stem, and break 

 off, leaving a scar, like the leaves of deciduous trees 

 in autumn (example, Polypodium) ; II. Desmobrya, 

 ferns whose fronds remain attached, and are pro- 

 duced from a crown (Aspidiuni) ; and, III. Scapho- 

 brya, fronds terminal, rising from between two 

 appendages, and articulated with the caudex (Ma- 

 rattid). Those sections he then subdivides into 



