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 Roses_ (published by the Linnean Society in 1863), he includes under the single species, Rosa canina--the common dog-rose--no less than twenty-eight named _varieties_ distinguished by more or less constant characters and often confined to special localities, and to these are referred about seventy of the _species_ of British and continental botanists.

Of the genus Rubus or bramble, _five_ British species are given in Bentham's _Handbook of the British Flora_, while in the fifth edition of Babington's _Manual of British Botany_, published about the same time, no less than _forty-five_ species are described.

Of willows (Salix) the same two works enumerate _fifteen_ and _thirty-one_ species respectively.