The question of the experimental origin of new species and varieties has
to be taken up from two widely separated starting points. This may be
inferred from what we have already seen concerning the two opposing
theories, derived and isolated from Darwin's original broad conception.
One of them considers mutations as the origin of new forms, while the
other assumes fluctuations to be the source of all evolution.

As mentioned above, my own experience has led me to accept the first
view. Therefore I shall have to show that mutations do yield new and
constant forms, while fluctuations are not adequate to do so. Retrograde
varieties and elementary species may both be seen to be produced by
sudden mutations. Varieties have often been observed to appear at once
and quite unexpectedly in horticulture and agriculture, and a survey of
these historical facts will be the subject of one of my lectures. In
some instances I have succeeded in repeating these observations in my
garden under the strict conditions of a scientific experiment, and these
instances teach us the real nature of the process of mutation in all its
visible features. New elementary [17] species are far more rare, but I
have discovered in the great evening-primrose, or _Oenothera
lamarckiana_ a strain which is producing them yearly in the wild state
as well as in my garden. These observations and pedigree-experiments
will be dealt with at due length in subsequent lectures.

Having proved the existence and importance of mutations, it remains to
inquire how far the improvements may go which are due only to
fluctuating variability. As the term indicates, this variability is
fluctuating to and fro, oscillating around an average type. It never
fails nor does it, under ordinary circumstances, depart far from the
fixed average.