Contrasting with
this wide variability is the stability of the yellow spot in the centre,
which is always present and becomes inconspicuous only, when the whole
petals are of the same hue. It is a general conception that colors and
color-markings are liable to great variability and do not constitute
reliable standards. But the cultures of Wittrock have proved the
contrary, at least in the case of the violets. No pattern, however
quaint, appears changeable, if one elementary species only is
considered. Hundreds of plants from seeds [44] from one locality may be
grown, and all will exhibit exactly the same markings. Most of these
forms are of very local occurrence. The most beautiful of all, the
_ornatissima_, is found only in Jemtland, the _aurobadia_ only in
Sodermanland, the anopetala_ in other localities in the same country,
the _roseola_ near Stockholm, and the yellow _lutescens_ in Finmarken.
The researches of Wittrock included only a small number of elementary
species, but every one who has observed the violets in the central parts
of Europe must be convinced that many dozens of constant forms of the
typical _Viola tricolor_ might easily be found and isolated.
We now come to the field pansy, the _Viola arvensis_, a very common weed
in the grain-fields of central Europe.
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