THE BRYOPHYTA 



115 



Fig. 51). The former constitute the wall of the anther- 

 idium, which remains one cell in thickness ; the central 

 cells undergo a 

 great number of 

 divisions, giving 

 rise to a small- 

 celled tissue,which , 

 when mature, is 

 entirely composed 

 of the mother-cells 



f ,-, , FIG. 51. Transverse section through the 



midrib of the thallus of Pellia, showing a 



zoids (Fi^. 52). young antheridium. an, antheridium ; o, 

 .._. . , ,, opening of the sheath surrounding the 



During the cell- antheridium. Magnified 80. (R. S.) 



division rapid 



growth of the whole organ goes on, and in the mean 

 time a wall of cells grows up around the antheridium, 



keeping pace with 

 its development, and 

 ultimately closing 

 it in, except for a 

 narrow opening at 

 the top (Figs. 51 

 and 52). 



This is the usual 

 course of anther- 

 idial development 

 in the Liverworts ; 

 the sheath, how- 

 ever, is not con- 

 stantly present. 



FIG. 52. Part of a similar section showing a There is also a 



nearly ripe antheridium. st, stalk of fairlv 

 anthc'ridium ; o, opening of sheath. Mag- * 



nified 80. (R. S. \ ment 



agree - 

 with the 



