THE BRYOPHYTA: MUSCI, THE MOSSES 



421 



From a superficial cell on the top of the receptacle a stalk cell is cut off 

 below, whilst the upper cell divides by three oblique walls, producing a 

 tetrahedral cell, with its apex projecting downwards and its spherical base 



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Fig. 404. — Mnium hornum. Apex of antheridium 

 showing the operculum by which the antheridium 

 opens. {After Lorch.) 



Involucral leaves • 



Paraphyses 



Archegonium 



Fig. 405. — Mnium hornum. Vertical section 

 through archegonial head showing archegonia, 

 paraphyses and involucral bracts. Note that 

 the axial conducting strand in the stem 

 terminates just below the gametoecium. 



