120 EVOLUTION OF PLANTS 
In the higher types it becomes more and more indepen- 
dent through the developmént 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 prob 
