296 MORPHOLOG V. 



large size which many of them attain. They occur chiefly in tropical moun- 

 tainous regions, many of them palm-like and imposing because of the large 

 trunks and leaves. Dicksonia, Cyathea, Cibotium, i\lsophila, are some of 

 the most conspicuous genera. 



Family Parkeriacecc. — There is a single species in this family (Ccra- 

 topteris thalictroides), abundant in the tropics and extending into Florida. 

 It is aquatic. 



Family Polypodiacc(F. — This family includes the larger numVicr of living 

 ferns and manv genera and species are found in North America. E.xam- 

 ples, Polypodium, Pteridium (=Pteris), Adiantum, etc. 



603. Order Hydropterales (or Salviniales). — The members of this order 

 are peculiar, aquatic ferns, some floating on the water (Azolla, Salvinia), 

 while others are anchored to the soil by roots (Marsilia, Pilularia). They 

 are known as water ferns. The sporangia are of two kinds, one containing 

 large spores (macrospores) and the other small spores (microspores). They 

 are therefore heterosporous ferns. 



Family Salviniacea^. — There are t\\'0 genera, Salvinia and Azolla. 

 Family Marsiliacea. — Two genera, Marsilia and Pilularia. In this family 

 the sporangia are enclosed in a sporocarp, whic h forms a pod-like structure. 

 CLASS EQUISETINEiE.* 



604. Order Equisetales. — The single order contains a single family, 

 Equisetacere, among the living forms, and but a single genus, Ef)uisetum. 

 There are about twenty-four species, with fourteen in the United States (see 



Chapter XXIX). 



CLASS LYCOPODIINE.ffi.f 



606. Order Lycopodiales. — The hrst two families of this order include 

 the homosporous L}'copodiine;e, while the Selaginellaceic are heterosporous. 



Family Lycopodiacecp. — There are two genera. Lvcopodium (club 

 moss) includes many species, most of them tropical, but a number in tem- 

 perate and subarctic regions. The gametophyte of many species is tuber- 

 ous, lacks chlorophyll, and in some there lives an endophytic fungus. Phyl- 

 loglossum with one species is found in .Au.stralia. 



Family Psilolacea'. — There are two genera. Psilotum chielh' in the 

 tropics has one species (P. triquelrum) in the region of Idnrida, 



Family Schigincllacecc. — These include the little club mosses, with one 

 genus, Selaginella (see Chapter XXX). 



CLASS ISOETINE.ffi:. 



606. Order Isoetales, with one famil\- Isoctace:e ami one genus Tsoetes 

 (see Chapter X.XXI). There are about hfty species, with aliout si.xteen in 

 the United States. 



* As class ]\quisetales in luigler and Prantl. 

 t As class Lycopodiales in Enpler and Prantl. 



