The above-mentioned elementary forms belong to the flora of southern
France, and Wittrock has isolated and cultivated a number of others from
the fields of Sweden. A species from Stockholm is called _Viola patens_;
_V. arvensis curtisepala_ occurs in Gotland, and _V. arvensis striolata_
is a distinct form, which has appeared in his cultures without its true
origin being ascertained.
The alpine violets comprise a more widespread type with some local
elementary species [46] derived exactly in the same way as the
tricolored field pansies.
Summarizing the general result of this description we see that the
original species _Viola tricolor_ may be split up into larger and lesser
groups of separate forms. These last prove to be constant in
pedigree-cultures, and therefore are to be considered as really existent
units. They are very numerous, comprising many dozens in each of the two
larger subdivisions.
All systematic grouping of these forms, and their combination into
subspecies and species rests on the comparative study of their
characters. The result of such studies must necessarily depend on
principles which underlie them. According to the choice of these
principles, the construction of the groups will be found to be
different. Wittrock trusts in the first place to morphologic characters,
and considers the development as passing from the more simple to the
more complex types.
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