It is
curious to note that the analogous variety of the European yew, _Taxus
baccata fastigiata_, though much more commonly cultivated than the
_Cephalotaxus_, never reverts, at least as far as I have been able to
ascertain. This clearly corroborates the explanation given above.
After considering these rare instances of more widely known reversions,
we may now examine the question of atavism from a broader point of view.
But in doing so it should once more be remembered, that all cases of
hybridism and also all varieties sporting annually or frequently, are to
be wholly excluded. Only the very rare occurrence of instances of
atavism in varieties that are for the rest known to be absolutely
constant, is to be considered.
Atavism or reversion is the falling back to a prototype. But what is a
prototype? We may take the word in a physiologic or in a systematic
sense. Physiologically the signification is a [171] very narrowly
restricted one; and includes only those ancestors from which a form is
known to have been derived. But such evidence is of course historic. If
a variety has been observed to spring from a definite species, and if
the circumstances have been sufficiently ascertained not to leave the
slightest doubt as to its pure origin, and if moreover all the evidence
has been duly recorded, we may say that the origin of the variety is
historically known.
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