In the present state of our knowledge it is very difficult to decide,
whether or not true reversion occurs in constant varieties. If it does
occur, it surely does so very rarely and only under unusual
circumstances, or in particular individuals. However when such
individuals are multiplied by buds and especially when they are the only
representatives of their type, the reversion, though theoretically rare,
will be shown by nearly every specimen of the variety. Examples of this
will be given below.
[156] They are generally called atavists or reversionists, but even
these terms are sometimes used in a different sense.
Lastly it is to be said that the empirical and experimental evidence as
to the question of constancy is not as extensive as it should be. The
experimental conditions are seldom described, and it is only recently
that an interest in the matter has been awakened. Much remains to be
done. Among other things the innumerable varieties of trees, shrubs and
perennial herbs should be tested as to their constancy when grown from
purely fertilized seeds. Many of them may be included among the number
that sport constantly.
Leaving aside the doubtful or insufficiently studied cases, we may now
turn our attention to the facts that prove the absolute stability of a
large number of varieties, at least as far as such completeness can be
attained by experiment or observation.
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