SECTION 17.] 



PTERIPOPHYTES. 



157 



side and discharge a great number of green spores of a size Urge enough 

 to be well seen by a hand-glass. The spores arc aided in their discharge 



494 



v.. 



and dissemination by four club-shaped threads attached to one part of them. 

 These are hygrometric : when moist they arc rolled 

 up over the spore ; when dry they straighten, 

 and exhibit lively movements, closing over the 

 spore when breathed upon, and unrolling promptly 

 a moment after as they dry. (See Fig. 493-493.) 

 4S6. Ferns, or Filices, a most attractive family 

 of plants, are very numerous and varied, in warm 

 and equable climates some rise into forest-trees, 

 with habit of Palms; but most of them are peren- 

 nial herbs. The wood of a Fern-trunk is very dif- 

 ferent, however, from that of a palm, or of any exogenous stem either. A 

 section is represented in Fiu r . 500. The curved plates of wood each ter- 



500 



Fig. 498. Upper part of a stem of a Horsetail, Eqnisetum aylvaticum. t'.'t. Part 

 of the head <>r Bpike of spore-cases, with s.mu- of the latter taken off. !!'.'•. View 

 (more enlarged) of under Bide of the Bhield-shaped body, bearing a circle of spore- 

 cases . 496. One <>f tin- latter detached and more magnified. l!'7. A --pore with 

 the attached arms moistened. 198. Same when dry, the anus extended. 



Fio. i 1 .''.'. A Tree-Fern, Dicksonia arboresoens, with a yonng one near it- base. 

 In front a common herbaceous Pern (Polypodium vulgare) with its creeping stem 

 or root stock. 



Fl(». 500. A section oi the trunk ut a Tree-Fern. 



