predisposition to it is pre-existent, for every acquired character is
simply the reaction of the organism upon a certain stimulus." (Vol. I,
p. 172.) Therefore the germ-cells do not inherit all the peculiarities
of the parents, but possess the predisposition or a potentiality of
the tendencies which gradually develop into individual characters.

We will be able to understand his theory better from the following
quotations, which give his own words. He says: "I have called this
substance 'germ-plasm,' and have assumed that it possesses a highly
complex structure, conferring upon it the power of developing into a
complex organism." ("Heredity," Vol. I, p. 170.) Again he says:
"There is, therefore, continuity of the germ-plasm from one generation
to another. One might represent the germ-plasm by the metaphor of a
long, creeping rootstock from which plants arise at intervals, these
latter representing the individuals of successive generations. Hence
it follows that the transmission of acquired characters is an
impossibility, for if the germ-plasm is not formed anew in each
individual, but is derived from that which preceded it, its structure,
and, above all, its molecular constitution, cannot depend upon the
individual in which it happens to occur, but such an individual only
forms, as it were, the nutritive soil at the expense of which the
germ-plasm grows, while the latter possessed its characteristic
structure from the beginning, viz., before the commencement of growth.
But the tendencies of heredity, of which the germ-plasm is the bearer,
depend upon this very molecular structure, and hence only those
characters can be transmitted through successive generations which
have been previously inherited, viz., those characters which were
potentially contained in the structure of the germ-plasm. It also
follows that those other characters which have been acquired by the
influence of special external conditions, during the lifetime of the