Apogamy in Ferns. 183 
with the premeiotic (unreduced) complement of chromosomes. In such 
a case there is no obstacle in the way of understanding that a sporophyte 
would naturally arise from the gametophyte by true apogamy, since the 
sporophytic number of chromosomes are already present. Such a view 
of the case would be further strengthened by a study of the polydactyla 
varieties of Lastrea. In them the prothallium is formed in the normal 
manner after meiosis, and the prothallial cells hence possess the postmeiotic 
(reduced) number of chromosomes. The embryo, it is true, is not the 
result of union of normal gametes, but nevertheless a nuclear fusion is 
concerned in its formation, and thus the full complement of sporophytic 
chromosomes is effected. 
Of course the aposporous prothallium of the Athyrium type presents 
its own difficulties, but they may be surmounted if we admit that the 
special potentialities of the duplicate number of chromosomes may be 
reduced to latency. If, however, we admit, as indeed the facts seem to com- 
pel us to do, that not only is the formation of the gametophyte independent 
of reduction, but a sporophyte may arise directly from a gametophyte 
which has itself arisen after meiosis , i. e. without a restoration of the normal 
sporophytic duplication of chromosomes, we implicitly give up the position 
that alternation of generations is necessarily bound up with the periodic 
alternation in the number of the chromosomes. That is, we admit that 
there is no common physiological basis for the two processes. 
We confess, however, that such a course seems to us to be the only one 
that is consistent with the facts. Of course it might be argued that, as in 
the variety polydactyla of Wills there is already evidence of a tendency 
towards reduction in number within the group of varieties, the var. cristata 
apospora only represents an extreme case. But apart from the improbability 
of such an explanation, having regard to the actual facts, we meet with 
great difficulties as soon as we refer to what is known about the origin 
of the variety. The nucleus of the spore which first found its way into the 
Wardian case must have only possessed the postmeiotic number of chromo- 
somes, that is, only half the number of those of the sporophyte which 
produced it. Consequently up to this point, and on the formation of the 
prothallium by its germination, the character of each of the gametophytes 
of the three varieties of Lastrea must have resembled each other. The 
divergence began in the formation of the embryo. For whereas in the two 
polydactyla varieties the premeiotic number of the young sporophyte was 
provided for by a fusion of prothallial nuclei, this process was omitted 
in the variety cristata apospora , and thus no mechanism was utilized to 
ensure that doubling of the typical gametophytic number of chromosomes 
that so commonly is associated with the production of the sporophyte. 
We shall defer the discussion as to the bearing of these conclusions on 
the question of alternation of generations to a later page. 
