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Apogamy in Ferns. 
probable that such an instance may turn up amongst these plants. If so, 
the spores on germination might give rise to prothallia consisting of 
premeiotic cells, and it would then be fairly safe to assume that any 
sporophytes formed on them would likewise be apogamously produced. 
We have purposely refrained from discussing those cases of apogamy 
in which nothing is known as to cytological details, as, for example, 
Balanophora , Ficus , Gnetum , Allium , and many others. For the assigning 
of these to their proper places can only be carried out when they have been 
reinvestigated from the point of view of their nuclear structure. 
Alternation of Generations. 
It is perhaps impossible, in dealing with the cytological aspect of 
apospory and apogamy, to avoid reference to questions involving views 
as to the nature of alternation of generations in the archegoniate 
plants. Within recent years a certain amount of cytological evidence 
has been woven into the fabric of theory, with the result that a conviction 
seems to have been formed in the minds of some botanists that the 
antithetic theory is in some way bound up with the periodic change in 
the number of the chromosomes. Consequently the facts that have now 
come to light, proving that gametophyte may rise directly from sporophyte, 
and sporophyte from gametophyte, without any such change on the part 
of the chromosomes, have been looked on as sapping the foundations 
on which the antithetic theory rests ; and, pro tanto , as supporting the 
views of those who advocate the theory of homologous alternation. As 
a matter of fact, it appears to us that they tend neither to destroy the one 
nor uphold the other. 
The periodic change in the number of chromosomes is primarily related 
to sexual fusion. Sexuality is a condition of meiosis, and meiosis in 
its turn renders the continuance of the sexual act a possibility ; at least 
this is a fair statement of the matter so far as our present knowledge 
is concerned. Just as sexuality is the common property of all the animals 
and plants alike (with sundry exceptions that in no way invalidate the 
general position), so also is meiosis. And the details of the mitoses 
included in the meiotic phase are extraordinarily similar in the two 
kingdoms . 1 Thus one would hardly be guilty of exaggeration in stating 
that, just as the fundamental importance of sexuality is rightly gauged from 
its almost universal occurrence, so also is that of the intimately related 
meiotic phase, regularly intercalated as it is in the life-cycle of every 
sexually reproducing animal and plant. 
1 Farmer and Moore, On the Essential Similarities existing between Heterotype Nuclear 
Divisions in Animals and Plants. Anat. Anzeiger, 1895. 
