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
nature of the change. For experimental purposes a single mutation does
not suffice; it must be studied repeatedly, and be produced more or less
arbitrarily, according to the nature of the problems to be solved. And
in order to do this, it is evidently not enough to have in hand the
mutated individual, but it is indispensable to have also the mutable
parents, or the mutable strain from which it sprang.
All conditions previous to the mutation are to be considered as of far
higher importance than all those subsequent to it.
Now mutations come unexpectedly, and if the ancestry of an accidental
mutation is to be known, it is of course necessary to keep accounts of
all the strains cultivated.
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