THE FERN ALLIES. 5 



ORDERS AND FAMILIES OF THE NORTH AMERICAN 



PTERIDOPHVTA. 

 SERIES I, —FERNS. 



Order i. — Ophioglossales. 



Family i. — Opkioglossacca:. 

 Order 2. — Filicales. 



Family i . — Hymenophyllacea. 



Family 2. — Osmimdacca\ 



Family 3. — Schizaacece. 



Family 4. — Ccraiopteridacea. 



Family 5. — PolypodiacecE. 



SERIES II. — FERN ALLIES. 



Order i. — Salvixiales. 



Family i, — MarsiliacecE. 



Family 2. — Salviniac'ece. 

 Order 2, — Equisetales. 



Fajiiily i. — Equisetaces, 

 Order 3. — Lycopodiales. 



Family i. — Lycopodiacece. 



Family 1. — Psilotacece. 



Family 3. — SclaginellacecE. 

 Order 4. — Isoetales. 



Fa III ily i . — I so eta cea. 



Like the ferns, the fern allies are reproduced by spores, 

 which, germinating-, forin. prothallia upon which the 

 reproductive organs, the antheridia and archegonia, are 

 borne. From the union of the contents of archegonia 

 and antheridia, new plants are produced. The pro- 

 thallia, however, are often quite unlike the familiar 

 green, heart-shaped prothallia of the fern. Some are 

 colourless, tuber-like, and develop underground instead of 

 upon the surface in the usual way, and in some that 

 develop above ground the prothallia are not heart- 

 shaped and the antheridia and archegonia are on sepa- 

 rate prothallia. The process of fertilization is essentially 



