ordinary pedigree-culture in practice. First the isolation of the
individuals and the study of individual inheritance, instead of
averages. Next comes the task of keeping records. Every individual must
be entered, its ancestry must be known as completely as possible, and
all its relations must be noted in such a form, that the most complete
reference is always possible. Mutations may come unexpectedly, and when
once arisen, their parents and grand-parents should be known. Records
must be available which will allow of a most complete knowledge of the
whole ancestral [22] line. This, and approximately this only, is the
essential difference between experimental and accidental observation.

Mutations are occurring from time to time in the wild state as well as
in horticulture and agriculture. A selection of the most interesting
instances will be given later. But in all such cases the experimental
proof is wanting. The observations as a rule, only began when the
mutation had made its appearance. A more or less vague remembrance about
the previous state of the plants in question might be available, though
even this is generally absent. But on doubtful points, concerning
possible crosses or possible introduction of foreign strains, mere
recollection is insufficient. The fact of the mutation may be very
probable, but the full proof is, of course, wanting. Such is the case
with the mutative origin of _Xanthium commune_ Wootoni from New Mexico
and of _Oenothera biennis cruciata_ from Holland. The same doubt exists
as to the origin of the _Capsella heegeri_ of Solms-Laubach, and of the
oldest recorded mutation, that of _Chelidonium laciniatum_ in Heidelberg
about 1600.

First, we have doubts about the fact itself. These, however, gradually
lose their importance in the increasing accumulation of evidence.
Secondly, the impossibility of a closer [23] inquiry into the real