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R. Ruggles Gates. 
formed in some instances and only a nucleus in others. In every 
case this ventral canal cell or nucleus is only a reminiscence which 
continues to reappear as a terminal stage although in its origin it 
dates back at least to the Liverworts. But it appears to be finally 
eliminated in the Taxodineae. The cases just cited, however, do not 
involve recapitulation so far as the individual ontogeny is concerned. 
They are only seen to be closely related to such phenomena from a 
comparative phylogenetic point of view. 
Such a reduction series Coulter (1915) no doubt justly con¬ 
siders to represent the expression of an orthogenetic tendency, 
though whether it is the result of climatic differentiation is not so 
clear. The series derives its interest from the fact that the higher 
Gymnosperms, in which the archegonium is quite eliminated, must 
have had ancestors in which that reduction gradually took place. 
From our present point of view, the explanation cannot be found 
in a series of successive nuclear variations or mutations, for these 
would make themselves felt in other parts of the organism, affecting 
many characters in a correlated fashion. Though the argument 
is by no means conclusive as regards this matter, yet it seems 
most reasonable to consider these as organismal characters and to 
explain the shortening of the gametophyte generation in the same way 
that recapitulatory characters find their explanation. The direction 
in which that explanation is to be sought will be discussed below. 
Another support for this view may be found in the fact that 
the chromosome number is remarkably uniform throughout the 
Gymnosperms, being, with few exceptions, 24. If the evolution of 
the Gymnosperms had taken place largely through mutations, i.e. t 
through changes arising in the germinal chromatin, one would expect 
it to have produced some effect on the chromatin morphology in the 
various species. The Angiosperms, by contrast, in which there is 
evidence that much mutation has taken place and is now going on, 
are characterized by remarkable variety in number, size and shape 
of their chromosomes even within single families or genera. The 
same is true of insects. 
Other cases of ancestral reminiscence in gametophytes, as 
though the organism repeated certain stages from force of habit or 
from some source of energy impelling its development forward, are 
to be found in Angiosperms. In the nuclear divisions within the 
embryo sac an evanescent cell-plate sometimes appears on the 
spindle. But this reminiscence of wall-formation soon disappears 
along with the spindles. The same is true of the prothallial cells 
