Sometimes they consist of two or three, or a few
elementary types, but in other cases they comprise twenty, or fifty, or
even hundreds of constant and well differentiated forms.
The inner constitution of these groups is however, not at all the same
in all cases. This will be seen by the description of some of the more
interesting of them. The European heartsease, from which our
garden-pansies have been chiefly derived, will serve as an example. The
garden-pansies are a hybrid race, won by crossing the _Viola tricolor_
with the large flowered and bright yellow _V. lutea_. They combine, as
everyone knows, in their wide range of [39] varieties, the attributes of
the latter with the peculiarities of the former species.
Besides the _lutea_, there are some other species, nearly allied to
tricolor, as for instance, _cornuta_, _calcarata_, and _altaica_, which
are combined with it under the head of _Melanium_ as a subgenus, and
which together constitute a systematic unity of undoubted value, but
ranging between the common conceptions of genus and species. These forms
are so nearly allied to the heartsease that they have of late been made
use of in crosses, in order to widen the range of variability of
garden-pansies.
_Viola tricolor_ is a common European weed. It is widely dispersed and
very abundant, growing in many localities in large numbers.
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