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-mother-cells, 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 (Zc, 
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. 
