120 EVOLUTION OF PLANTS 



In the higher types it becomes more and more indepen- 

 dent through the development of green assimilative 

 tissues. This reaches its highest expression in- Antho- 

 ceros and the Musci. 



The latter group is probably the most modern and 

 specialized one. This is indicated both by the greater 

 number of species and their wider distribution, as well 

 as by a much more stereotyped structure. These have 

 probably arisen from liverworts resembling Anthoceros, 

 and it is not likely that they have given rise to any 

 higher forms, but represent the end of their own special 

 line of development. 



In the evolution of the sporophyte there has been 

 little external differentiation, the most highly special- 

 ized forms being found in the Musci, where the sporo- 

 phyte shows a foot seta and capsule ; but there are no 

 leaves or other appendicular organs, although the pecul- 

 iar apophysis found in a few mosses perhaps approaches 

 this condition. 



In Anthoceros, although the external differentiation 

 is very slight, there is one respect in which it stands 

 alone, i.e. the unlimited growth of the sporophyte. 

 This, in connection with the highly developed assimila- 

 tive tissue, makes the sporophyte of this plant the near- 

 est approach to the entirely independent sporophyte of 

 the ferns. Were the foot of the sporophyte in Antho- 

 ceros prolonged into a root penetrating the earth, it 

 would become quite independent of the gametophyte, 

 and were a special assimilate organ or leaf developed, a 

 condition directly comparable to the sporophyte of the 

 lower Pteridophytes or ferns would result. It is prot> 



