PTERIDOPHYTES. 



157 



side and discharge a great miniber of green spores of a size large enough 

 to be well seen by a baud-glass. Tlie spores are aided in tlieir discharge 

 494 



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

 These are hygrometric : wlieu moist tliey are rolled 

 up over the spore ; when dry they straighten, 

 ai>d exhibit lively movements, closing over the 

 spore when breathed upon, and unrolling jiromptly 

 a momei>t after as they dry. (See Fig. 493-498.) 

 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. Tlie wood of a Feru-trunk is very dif- 

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

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



F;G. 493. Upper part of a .stem of a Horsetail, Equisetuin .sylvaticuiii. 494. Part 

 of the head or spike of spore-cases, with some of the latter taken off. 495. View 

 (more eiilargerl) of uniler side of the sliield-shaped body, bearing a circle of spore- 

 cases. 496. One of tlie latter detached and more magnified. 497. A spore with 

 the attached arms moistened. 498. Same when dry, the arms extended. 



Fig. 499. A Tree-Fern, Dick.sonia arboreseens, with a young one near its base. 

 In front a common herbaceous Fern (I'olypodiiiin vulgare) witli its creexnng stem 

 or rootstock. 



Flo. 500- A section of the trunk of a Tree-Fern 



