62 ALTERNATING GENERATIONS 



show normally the regular succession of events as described, viz. the 

 haploid gametophyte leading through sexuality to the diploid sporophyte, 

 which, again, through reduction or meiosis in the spore-mothepcells, leads 

 back to the haploid prothallus. The constancy of this is too great 

 to allow its recognition as the " normal " to be seriously disturbed by 

 the occasional irregularities described irregularities which bear all the 

 characters of late, individual, and probably non-permanent aberrations. 

 Their existence is suggestive on certain points, but it cannot be held to 

 invalidate the view that the cycle as above stated existed in all probability 

 throughout the earlier phases of descent of the Archegoniatae. 



Accordingly the cytological distinction of the two generations may be 

 upheld as the normal condition for the Archegoniatae. Further, the opinion 

 of Farmer may be accepted, that the new facts relating to apogamy and 

 apospory leave the question of alternation where it was : they tend neither 

 to destroy the one theory of its origin nor to uphold the other (I.e., 

 p. 193). Moreover, the facts of the normal chromosome-difference may be 

 held to accord with either of the theories of alternation, the homologous 

 or the antithetic : they are not finally distinctive for either, and a decision 

 must remain still in doubt until the actual history of the genesis of the 

 diploid phase in the Archegoniatae can be traced. Towards forming a 

 just opinion on this question it is desirable not only to compare the 

 Archegoniatae among themselves, but also to take into consideration 

 the life-cycles of the Thallophytes ; for these plants often show a simpler 

 mode of life, and have always been held to afford suggestions as to the 

 probable origin of the more complex land-vegetation. This will be the 

 subject of the next chapter. 



