430 



MOSSES AND FERNS 



CHAP. 



in the older prothallia similar but much shorter and broader 

 lobes arise alternately from either side of the growing apex. 



The development of the archegonium is intimately asso- 

 ciated with the formation of the lobes. The archegonium 

 mother cell is formed close to the base of the young lobe upon 

 the ventral side. By subsequent growth of the tissue between 

 it and the apical meristem, it is subsequently forced to the 

 upper side, but its origin is ventral, as in the Ferns. The 

 lobe at whose base it is borne grows for some time by a 



Fig. 223. — Development of the archegonium. A, Optical section of the very young archegonial 

 meristem, X225; B-E, longitudinal sections of young archegonia, X450; c, neck canal cell; v, 

 ventral canal cell ; 0, egg. 



definite apical cell, which is very evident in horizontal sections 

 (Fig. 224, C). 



The development of the archegonium most nearly resembles 

 that of the eusporangiate Ferns. Usually, but not always, no 

 basal cell is formed, and the first division in the inner ceil 

 separates the neck canal cell from the central cell. Both neck 

 and ventral canal cells (Fig. 223, E) equal in breadth the 

 central cell, and in this respect are most like the Marattiaceae. 

 The neck canal cell later grows up between the neck cells, but 

 there is usually a space between its summit and the terminal 

 neck cells, which here are much longer than the others. It 



