PHYLETIC DELAY IN REDUCTION 77 
reduction, follows on nuclear fusion, while in Rfopalodia these events 
precede nuclear fusion. Such cases seem to point to a probability that 
the problem of reduction was solved independently and in different ways 
in different lines of descent. 
Nevertheless the term sporophyte has been adopted as applicable 
collectively to the non-sexual phase which intervenes between sexual fusion 
and reduction in those plants in which it occurs. But, following the above 
reasoning, it must not be understood to convey necessarily any community 
of descent for all the bodies which it covers. It seems probable that the 
establishment of the sporophyte, whether by a process of intercalation or 
otherwise, has taken place independently in several distinct phyla: thus 
the sporophyte-stage in them, though in some more lax sense it may be 
styled “homologous,” is not to be held as ‘“homogenetic”; nevertheless, 
useful analogies may be drawn between the corresponding phases in 
distinct phyletic lines. 
But, on the other hand, comparison within groups that are held to be 
akin gives strong reason for recognising that there has been a shifting of 
position of the event of chromosome-reduction in certain lines of descent, 
and that the balance of the generations has thus been altered in the 
evolutionary course. For instance, it seems probable that in the Uredineae 
there has been a deferring of the event of reduction after sexuality, with the 
result that the binuclear phase has attained considerable dimensions ; the 
same seems probable also for the Ascomycetous Fungi, though along a quite 
distinct line. A similar intercalation has been suggested in the Florideae. 
Such conclusions can only become cogent when the cytological details are 
known in a large number of related forms, But the most familiar, and at 
the same time the most prominent and permanent example is that of the 
Archegoniatae: in these there is a strong comparative basis for the belief 
that the sporophyte stage has been intercalated, or in any case greatly 
extended, in consequence of the deferring of the event of chromosome- 
reduction. It may be a question whether the post-sexual stage in the 
life-history of certain green Algae represents any phyletic predecessor of the 
sporophyte of the Archegoniatae : it is quite probable that it did not. But 
this much is clear, that it occupies the same position in the life-cycle, and 
it gives at least the suggestion how the Archegoniate sporophyte may 
have originated. According to the antithetic theory as applied to the 
Archegoniatae, the complications of post-sexual nuclear reduction, involv- 
ing, as they are seen to do, at least four nucleated cells, supplied the 
starting-point for a diploid somatic expansion. That is the theory which 
is adopted here as reflecting the probable mode of origin of the. alternation 
in the Archegoniate series. But it is only right to acknowledge that it 
is not fully demonstrated either by the cytological facts, or by comparison 
with the alternation in the Thallophytes. The latter can only supply 
suggestive analogies so long as the actual phyletic origin of the Archegoniatae 
remains as obscure as it now is. It becomes, accordingly, an object of all 
