476 



BOTANY OF THE LIVING PLANT 



On the other hand, certain Liverworts have very simple sporogonia. 

 This is conspicuously the case in the Ricciaceae (Fig. 372), where it is 

 spherical, with no distinction of apex and base, and no elaters. The 

 sporogonial wall is one layer thick, and is disorganised at ripeness. 



Fig. 372. 



Ricciocarpits natans. Young sporogonia still surrounded by the archegonial 

 wall. The younger ( x 666) shows the wall of the sporogonium shaded, surrounding 

 the sporogenous cells. In the older ( x 560), these are separated as the free 

 spore-mother-cells. (After Garber.) 



The spores are scattered on decay of the thallus. This is the simplest 

 condition of the sporophyte known in Archegoniate Plants. It is a 

 familiar subject of comparative discussion whether the simplicity 

 that Riccia shows is really primitive or the result of reduction from 

 some more complex type. 



Comparing the facts from the Mosses and Liverworts it is apparent 

 that both are " amphibians " in the sense that they live on exposed 

 land-surfaces, but cannot complete their life-cycle without the 

 presence of external liquid water. This tends to restrict them to 

 moist situations. In any organism with a life-cycle punctuated by 

 the two stages of the spore and the zygote, there are two possibilities 

 of somatic expansion, viz. in the diploid sporophyte and in the haploid 



