210 CLASS CRYPTOGAM! A. 



Their composition presents a fine lace-like net-work, 

 or labyrinth of veins or vessels. The fructification, with- 

 out any proper visible flowers, is seen commonly to 

 occupy the under surface of the frond, in the form of 

 round or oblong dots, or marginal lines, turning brown 

 on attaining maturity. These mere dust-like spots 

 and lines, when examined through a good micros- 

 cope, are found to consist of dense clusters (botanical- 

 ly termed sori), of minute, flattish, circular capsules, 

 at first entire, but afterwards bursting elastically and 

 irregularly through the contractions of the jointed ring 

 by which each o! them is respectively surrounded. 

 They contained seed or spone, as it is called, differing 

 from ordinary seed, is like an impalpable powder, as 

 light commonly as the air, and wafted abroad to any 

 height or distance, so that it is not surprising to per- 

 ceive Ferns growing high on the trunks of trees, or 

 on the summits of lofty and ruined buildings. That 

 they are not more common, may be accounted for, in 

 the absence of tbe great degree of requisite moisture 

 and shade necessary to their germination and growth. 



The Ferns present two very distinct divisions of 

 kindred genera : namely, those which produce their 

 sori on the under side of the fronds, and have cap- 

 sules surrounded with the articulated ring ; and oth- 

 ers, such as the Osmunda, which have rather conspic- 

 uous, bivalvular capsules, like two cups edge to edge, 

 without the jointed ring, and collected together, either 

 on a separate independent frond, or on distinct parts 

 ef one. 



The common Polypody (Polypodium vidga re) often 

 green throughout the winter, and growing on the shelv- 

 ings of moist shady rocks, will afford a familiar example, 

 of the true or dorsiferous Ferns ; that is, such as have 

 die fruit on the under side of the frond, and furnished 

 with the jointed ring. In this genus, the sori (or 



