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: (i) 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. 



