such variation is independent of any
change in the conditions of nutrition or environment which may operate upon
the individual producing the gametes.

But, as everybody knows, an individual organism, whether plant or animal,
reacts, and often reacts markedly, to the environmental conditions under
which its life is passed. More especially is this to be seen where such
characters as size or weight are concerned. More sunlight or a richer soil
may mean stronger growth in a plant, better nutrition may result in a finer
animal, superior education may lead to a more intelligent man. But although
the changed conditions produce a direct effect upon the individual, we have
no indisputable evidence that such alterations are connected with
alterations in the nature of the gametes which the individual produces. And
without this such variations cannot be perpetuated through heredity, but
the conditions which produce the effect must always be renewed in each
{138} successive generation. We are led, therefore, to the conclusion that
two sorts of variations exist, those which are due to the presence of
specific factors in the organism and those which are due to the direct
effect of the environment during its lifetime. The former are known as
_mutations_, and are inherited according to the Mendelian scheme; the
latter have been termed _fluctuations_, and at present we have no valid
reason for supposing that they are ever inherited. For though instances may
be found in which effects produced during the lifetime of the individual
would appear to affect the offspring, this is not necessarily due to
heredity. Thus plants which are poorly nourished and grown under adverse
conditions may set seed from which come plants that are smaller than the
normal although grown under most favorable conditions. It is natural to
attribute the smaller size of the offspring to the conditions under which
the parents were grown, and there is no doubt that we should be quite right
in doing so. Nevertheless, it need have nothing to do with heredity. As we
have already pointed out, the seed is a larval plant which draws its
nourishment from the mother. The size of the offspring is affected because
the poorly nourished parent offered a bad environment to the young plant,
and not because the gametes of the parent were changed through the adverse
conditions under which it grew. The parent in this case is not only the
producer of gametes, but also a part of the envir