142 MORPHOLOGY. 



313. Embryo. — In the plants which we have selected thus far for study, 

 the egg, immediately after fecundation, we recollect, passed into a resting 

 state, and was enclosed by a thick protecting wall. But in riccia, and in the 

 other plants of the group which we are now studying, this is not the case. 



Fig. 172. Fig. 173. 



Archegonium of riccia, showing neck, Young embryo (sporogoni- 



venter, and the egg; archegonium is partly um) of riccia,within the venter 



surrounded by the tissue of the thallus. of the archegonium ; the latter 



(Riccia crystallina.) has now two layers of cells. 



(Riccia crystallina. j 



The egg, on the other hand, after acquiring a thin wall, swells up and fills 

 the cavity of the venter. Then it divides by a cross wall into two cells. 

 These two grow, and divide again, and so on until there is formed a quite 

 large mass of cells rounded in form and still contained in the venter of the 

 archegonium, which itself increases in size by the growth of the cells of the 

 wall. 



313. Sporogonium of riccia. — The fruit of riccia, which is 

 developed from the fertiUzed egg in the archegonium, forms a 

 rounded capsule still enclosed in the venter of the archegonium, 

 which grows also to provide space for it. Therefore a section 

 through the plant at this time, as described for the study 

 of the archegonium, should show this capsule. The capsule 

 then is a rounded mass of cells developed from the egg. A sin- 

 gle outer layer of cells forms the wall, and therefore is sterile. 



