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 



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



ot the spermato- midrib of the thallus of Pellia ^ sho wing a 



zoids (Fig, 52). young antheridium. an, antheridium ; o, 

 T, . ,, ,, 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 f a i r 1 v P l O q P qrrrpp 



antheridram ; 0, opening of sheath. Mag- taH V clc ' a g ie 



nified 80. (R. S.l llient with the 



