368 



BOTANY OF THE LIVING PLANT 



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

 This is conspicuously the case in the Ricciaceae (Fig. 313), 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. 312. 



A, Ripe capsule of Aneiira pingiiis in longitudinal section. From the summit an 

 elaterophore hangs into the spore-cavity, in which are many spores and detached 

 elaters. Magnified. (After Goebel.) 



B, Capsule of PelUa calycina, burst, and emptied, showing the valves of the wall 

 recurved, and an elaterophore rising from the base, bearing many threads. (After 

 Goebel.) 



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 such facts from the Bryophyta with those relating to 

 the Pteridophyta, it is apparent that both are " amphibians," in the 

 sense that they cannot complete their life-cycle without the presence 

 of externa] fluid water. This tends to. restrict them to moist situations, 

 where their sexual propagation by motile spermatozoids can be carried 



