BKYOPHYTES 



95 



Sporophyte. — The fertilized egg (fig. 220) produces the sporophyte 

 (called sporogonium in the bryophytes), which when mature is a spherical 

 body, consisting of a wall layer of sterile cells investing a mass of spo- 

 rogenous cells (figs. 221- 

 226). In producing this 

 body the egg by succes- 

 sive divisions usually 

 first becomes a sphere 

 of eight cells (octants). 

 Then periclinal (parallel 

 with the surface) walls 

 cut ofT an outer layer of 

 cells (amphitkeciiim) that 

 forms the wall of the 

 sporophyte. The group 

 of inner cells is the 

 endothecium, which by 

 successive divisions pro- 

 duces a mass of sporog- 

 enous tissue. The cells 

 produced by the last 

 divisions of the sporog- 

 enous tissue are the spore 

 mother cells, each of 

 which produces a tetrad 

 of spores (fig. 226), dur- 

 ing which process the 

 reduction in the number 

 of chromosomes occurs. 

 The mature sporophyte, 

 therefore, is simply a 

 spore case. The venter 

 of the archegonium 

 grows also, forming a 

 special investing struc- 

 ture, the calyptra (fig. 

 225). Finally the wall layer of the sporophyte and the layers of the 

 calyptra become disorganized, and the spores are free in the archegonial 

 chamber. The spores upon germination produce the gametophyte body. 



Figs. 205-211. — Riccia: development of the an- 

 theridium; 205, first division of the superficial initial 

 cell, the protruding cell to give rise to the antheridium ; 



206, first transverse division of the antheridial cell; 



207, further transverse divisions; 208, the beginning of 

 vertical walls; 209, completion of periclinal walls sepa- 

 rating the wall of the antheridium from the spermatog- 

 enous cells; 210, an almost mature antheridium, show- 

 ing the short stalk, the wall, and the mass of cubical 

 spermatogenous cells in conspicuous blocks; 211, a 

 sperm, showing the biciliate bryophytic type (body of 

 sperm black ; adjacent light mass is cytoplasm dragged 

 out of the mother cell) . 



