mean about which the observed forms vary. Almost every character may be
developed to a greater or a less degree, but the variations of the single
characters producing a small deviation from the mean are usually the
commonest. The limits of these fluctuations may be called wide or narrow,
according to the way we look at them, but in numerous cases the extreme on
the favoured side hardly surpasses double the value of that on the other
side. The degree of this development, for every individual and for every
organ, is dependent mainly on nutrition. Better nourishment or an
increased supply of food produces a higher development; only it is not
always easy to determine which direction is the fuller and which is the
poorer one. The differences among individuals grown from different seeds
are described as examples of individual variability, but those which may be
observed on the same plant, or on cuttings, bulbs or roots derived from one
individual are referred to as cases of partial variability. Partial
variability, therefore, determines the differences among the flowers,
fruits, leaves or branches of one individual: in the main, it follows the
same laws as individual variability, but the position of a branch on a
plant also determines its strength, and the part it may take in the
nourishment of the whole. Composite flowers and umbels therefore have, as
a rule, fewer rays on weak branches than on the strong main ones. The
number of carpels in the fruits of poppies becomes very small on the weak
lateral branches, which are produced towards the autumn, as well as on
crowded, and therefore on weakened individuals. Double flowers follow the
same rule, and numerous other instances could easily be adduced.

Mutating variability occurs along three main lines. Either a character may
disappear, or, as we now say, become latent; or a latent character may
reappear, reproducing thereby a character which was once prominent in more
or less remote ancestors. The third and most interesting case is that of
the production of quite new characters which never existed in the