ANTHOCEROTALES 271 
with the facts. These suggest rather the influence of nutritive factors 
acting on the young embryo while still enclosed in the tissue of the 
gametophyte. 
The characters of progress achieved by the more complex Antho- 
cerotales, in advance of the Jungermanniales, appear accordingly to be 
these: (1) a continued intercalary growth at the base, originating from 
the seta, and giving an unlimited sequence of spore-production; (2) 
provision for the nourishment and ultimate dispersal of the spores by 
means of the columella; (3) relegation of spore-development to a more 
superficial source, as the sterilisation at the centre becomes established ; 
and (4) development of an assimilatory apparatus for self-nourishment 
from the tissues of the capsular wall. All these advances are readily 
intelligible on biological grounds, and are due either directly to steri- 
lisation of fertile cells, or to secondary modifications in tissues already 
sterile in the simpler types. The theory of progressive sterilisation has. 
already been traced in its application to the sporogonia of other 
Liverworts, as elucidating the origin of the protective capsular wall, 
the seta, the elaters, and elaterophores. It is now seen that the origin 
of the sporogonium of the Anthocerotales, though the most advanced of 
all the Hepaticae, falls naturally within the lines of a theory of progressive 
sterilisation, which starts from relatively simple post-sexual cell-divisions. 
