230 BRYOPHYTA. [CH- 



On the germination of the spore there i? usually formed a fairly 

 distinct structure known as the protonema, from which the 

 Moss or Liverwort developes as a bud^. 



fMARCHANTIALES. 

 ANTHOCEEOTALES. 

 JUNGERMANNIALES. 



The vegetative plant-body possesses a different organisation 

 on the ventral and dorsal side ; it has the form of a thalloid 

 creeping plant (Thalloid Liverworts), or of a delicate stem with 

 thin appendages or leaves without a midrib (Foliose Liver- 

 worts). In most cases the body of the plant is made up of 

 parenchymatous tissue, showing but little internal differen- 

 tiation ; in one or two genera a few strengthening or mechanical 

 fibres occur among the thinner walled ground-tissue. On the 

 germination of the spore, a feebly developed protonema is 

 produced, which gives rise tp the Liverwort plant. Repro- 

 duction as in the group Bryophyta. 



The Liverworts have a very wide geographical distribution, 

 and are specially abundant in moist shady situations; they 

 grow on stones or damp soil, and occur as epiphytes on other 

 plants. Marchantia, Pellia, and Jungermannia are among the 

 better known British representatives of the class. 



Considering the soft nature of the body of recent Liver- 

 worts, it is not surprising that they are poorly represented in a 

 fossil state. In the absence of the sexual reproductive organs, 

 or of the sporophytes, which have scarcely ever been preserved, 

 exact identification is almost hopeless. The difficulties already 

 referred to in dealing with the algae, as regards the misleading 

 similarity between the form of the thallus and the bodies of 

 other plants, have to be faced in the case of the Liverworts. 

 Many of the thalloid Liverworts, if preserved in the form of a 

 cast or impression without internal structure or reproductive 

 organs, could hardly be distinguished from various genera of 

 algae in which the thallus has the form of a forked plate-like 



1 Sohifiner and Mtiller in Engler and Prautl (95), Campbell (95), Dixon and 

 Jameson (96) are among the best of modern writers on the Bryophyta. 



