The petals are as a rule obcordate, but this type may be combined
with others having more or less broad emarginations at the summit, and
with differences in breadth which vary from almost linear types to
others which touch along their margins. The pods are short and broad, or
long and narrow, or varying in sundry other [49] ways. All in all there
are constant differences which are so great that it has been possible to
distinguish and to describe large numbers of types.
Many of them have been tested as to their constancy from seed. Jordan
made numerous cultures, some of which lasted ten or twelve years; Thuret
has verified the assertion concerning their constancy by cultures
extending over seven years in some instances; Villars and de Bary made
numerous trials of shorter duration. All agree as to the main points.
The local races are uniform and come true from seed; the variability of
the species is not of a fluctuating, but of a polymorphous nature. A
given elementary species keeps within its limits and cannot vary beyond
them, but the whole group gives the impression of variability by its
wide range of distinct, but nearly allied forms.
The geographic distribution of these elementary species of the
whitlow-grass is quite distinct from that of the violets. Here
predominant species are limited to restricted localities.
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