THE FERN ALLIES. 5 



ORDERS AND FAMILIES OF THE NORTH AMERICAN 

 PTERIDOPHYTA. 



SERIES I. FERNS. 



ORDER i. OPHIOGLOSSALES. 



Family I. Ophioglossacetc. 

 ORDER 2. FILICALES. 



Family i . Hymenopkyllacece. 



Family 2. Osmundacece. 



Fa m ily 3 . Sell izcea cece. 



Family 4. Ccratopteridacece. 



Family 5. Polypodiacece. 



SERIES II. FERN ALLIES. 



ORDER i. SALVINIALES. 



Family i . Marsiliacece. 



Family 2. Salviniacece. 

 ORDER 2. EQUISETALES. 



Family i. Equisetacece, 

 ORDER 3. LYCOPODIALES. 



Fa mily \ . Lycopodia cece. 



Family 2. Psilotacece. 



Family 3. Selaginellacece. 

 ORDER 4. ISOETALES. 



Fa m ily i . Isocta cece. 



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

 which, germinating, form 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 



