und that their yellow crocuses were eaten by
sparrows, while the blue, purple, and white coloured varieties were left
untouched; but Mr. Tegetmeier, who grows only these latter colours,
found that after two years the sparrows began to attack them, and
thereafter destroyed them quite as readily as the yellow ones; and he
believes it was merely because some bolder sparrow than the rest set the
example. On this subject Mr. Charles C. Abbott well remarks: "In
studying the habits of our American birds--and I suppose it is true of
birds everywhere--it must at all times be remembered that there is less
stability in the habits of birds than is usually supposed; and no
account of the habits of any one species will exactly detail the various
features of its habits as they really are, in every portion of the
territory it inhabits."[27]

Mr. Charles Dixon has recorded a remarkable change in the mode of
nest-building of some common chaffinches which were taken to New Zealand
and turned out there. He says: "The cup of the nest is small, loosely
put together, apparently lined with feathers, and the walls of the
structure are prolonged for about 18 inches, and hang loosely down the
side of the supporting branch. The whole structure bears some
resemblance to the nests of the hangnests (Icteridae), with the
exception that the cavity is at the top. Clearly these New Zealand
chaffinches were at a loss for a design when fabricating their nest.
They had no standard to work by, no nests of their own kind to copy, no
older birds to give them any instruction, and the result is the abnormal
structure I have just described."[28]

These few examples are sufficient to show that both the habits and
instincts of animals are subject to variation; and had we a sufficient
number of detailed observations we should probably find that these
variations were as numerous, as diverse in character, as large in
amount, and as independent of each other as those which we have seen to
characterise their bodily structure.

_The Variability of Plants._

The variability of plants is notorious, being proved not only by the
endless variations which occur whenever a species is largely grown by
horticulturists, but also by the great difficulty that is felt by
botanists in determining the limits of species in many large genera. As
examples we may take the roses, the brambles, and the willows as well
illustrating this fact. In Mr. Baker's _Revision of the British Rose