FRUCTIFICATION OF FERNS. 



377 



Fig. 189. 



it upon the Glass Stage-plate, or to hold it in the Stage-Forceps, 

 and to throw an adequate light upon it by the Side-condenser. It 

 usually presents itself in the form of isolated spots on the under 

 surface of the frond, termed Sort, as in the common Polypodium 

 (Fig. 189) and in the Aspidium (Fig. 190) ; but sometimes these 

 ' sori ' are elongated into bands, as in the common Scolopendrum 

 (Hart's-tongue) : and these bands may coalesce with each other, 

 so as almost to cover the surface of 

 the frond with a network, as in 

 Hcemionitis (Fig. 190) ; or they may 

 form merely a single band along its 

 borders, as in the common Pteris 

 (brake-fern). The Sori are sometimes 

 1 naked ' on the under surface of the 

 fronds ; but they are frequently covered 

 with a delicate membrane termed the 

 Indusium, which may either form a 

 sort of cap upon the summit of each 

 sorus, as in Aspidium (Fig. 191), or a 

 long fold, as in Scolopendrum and 

 Pteris; or a sort of cup, as in De- 

 paria (Fig. 192). Each of these sori, 

 when sufficiently magnified, is found 

 to be made up of a multitude of Cap- 

 sules or Thecce (Figs. 191, 192), which 

 are sometimes closely attached to the 

 surface of the frond, but more com- 

 monly spring from it by a pedicle or 

 footstalk. The wall of the Theca 

 is composed of flattened cells, applied 

 to each other by their edges ; but there 

 is generally one row of these thicker 

 and larger than the rest, which springs 

 from the pedicle, and is continued over 

 the summit of the capsule, so as to 

 form a projecting Ring, which is known 

 as the Annulus. This Ring has an 

 elasticity superior to that of all the 

 rest of the capsular wall, causing it to 

 split across when mature, so that the 



contained spores may escape ; and in many instances carrying the 

 two halves of the Capsule widely apart from each other (Fig. 192), 

 the fissure extending to such a depth as to separate them completely. 

 It will frequently happen that specimens of Fern-fructification 

 gathered for the Microscope will be found to have all the Capsules 

 burst and the Spores dispersed, whilst in others less advanced the 

 Capsules may all be closed; others, however, may often be met with 

 in which some of the Capsules are.closed and others are open ; and 



Leaflet of Polypodium, 

 with Sori. 



