MANUAL OF NATURAL HISTORY. 525 



I. ORDER.— Filicals (Filicales). 



Vascular; spore-cases marginal or dorsal, 1 -celled, 

 usually surrounded by an elastic ring ; spores of 

 only one kind. 



1. Family. — Dancea-worts (Danseaceae). Occasion- 



ally arboriform ; spore-cases exannulate, ap- 

 pearing sunk within, or seated upon the back 

 of the leaflets, conjoined more or less by their 

 inner faces, opening irregularly by a central 

 cleft. Tropical species in both hemispheres. 



2. Family. — Ferns (Polypodiacese). Herbaceous, 



shrubby, or aborescent ; spore-cases on the 

 back or edge of the fronds, pedicellate or ses- 

 sile, distinct, annulate, bursting irregularly. 

 Inhabit especially moist, insular situations, 

 and are very abundant in tropical islands ; 

 less numerous on continents. Some, as JVe- 

 phrodium Filix-mas, have been used in 

 medicine. 



3. Family. — Adder' s-tongues (Ophioglossacese). 



Herbaceous; spore-cases exannulate, distinct, 

 2-valved, collected into a spike formed out of 

 the sides of an altered frond. Principally 

 select tropical, insular situations, but occur 

 also in temperate regions. 



II. ORDER. — Lycopodals (Lycopodales). 



Vascular ; spore-cases axillary or radical, 1- or 

 many-celled ; spores of two kinds. 

 1. Family. — Pepper-worts (Marsileacese). Herba- 



