PELLIA. 31 F 



(6) The median thickened portion or midrib, passing on 

 either side into the thin lateral portions or wings. 



(c) At the anterior end of each branch the notch in 

 which lies the apical growing-point. 



(d) The unbranched rhizoids springing from the pro- 

 jecting underside of the midrib. 



In fertile plants, note, according to the time of year, 

 (e} The autheridial cavities, wart-like projections 

 scattered over the upper side of the midrib, each with .a 

 small pore at its apex slit the cavity open, to see the 

 small spherical anther idium which it contains. 



(/) The archegonial cavity near the anterior end of 

 a branch, forming a pocket open in front and extending 

 backwards into the tissue of the midrib, the opening of the 

 pocket protected by 



(g) A flap (involucre) of thallus-tissue projecting over 

 it from behind slit the cavity: open, to see the group of 

 hair-like archegonia springing from its closed posterior 

 end. 



(h) The sporogonium, which may be in one of the fol- 

 lowing stages (1) in process of development, enclosed in the 

 calyptra, (2) ripe and showing the dark -coloured spherical 

 capsule lying just within or slightly projecting from the 

 opening of the cavity, with the seta still very short, (3) 

 the ripe capsule carried up by elongation of the seta to a 

 height of as much as 8 or 10 cm., (4) the dehiscence of the 

 capsule by splitting of its wall into four valves which open 

 outwards and downwards, exposing the mop-like tuft of 

 elaters and spores, (5) collapse of the seta shortly after the 

 dispersal of the spores, and the persistence for some time 

 of the four capsule-valves and the tuft (elaterophore) of 

 fixed elaters. 



459. Structure of Thallus. (a) Cut transverse 

 sections of the thallus at different places. Some of 

 the sections should include antheridial cavities ( 460). 

 Note (1) the form of the section, with the midrib project- 

 ing below and thinning out to a single layer of cells at the 



